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Guidebook for Energy Facilities Compatibility with Airports and Airspace (2014)

Chapter: Chapter 3 - Energy Technologies and Aviation Safety Impacts

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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Chapter 3 - Energy Technologies and Aviation Safety Impacts." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

20 Energy Technologies and Aviation Safety Impacts This chapter provides a review of research and industry trends related to the following energy technologies, which present certain aviation safety challenges: solar, wind, oil and gas drilling, conventional power plants, and electricity transmission. Each section pertains to a particular technology type, beginning with the context for examining aviation safety issues for each technology, along with the research objectives for this project. After this introductory section, an overview of the technology is presented, followed by potential aviation impacts, methods to assess and manage impact, applicable experiences with these technologies in the aviation environ- ment, and lessons learned that inform guidelines and best practices. Finally, in-depth case studies of specific energy projects at or near airports are used to demonstrate relevant issues and potential solutions. 3.1 Solar Power 3.1.1 Research Context The deployment of solar power has expanded throughout the United States over the past 5 years. Annual solar installa- tions have increased tenfold since 2008, from about 300 MW to over 3,000 MW in 2012. Decreasing costs of solar electric- ity have driven this growth, as indicated by a 60% reduction in the cost of solar panels over the past 2 years. In addition to lower solar costs, a variety of incentives are also creating a burgeoning solar market, including tax credits, purchas- ing mandates by federal agencies, and state-level renewable energy portfolio standards (RPS). The amount of electric- ity produced by solar in the United States is now enough to power 1.3 million homes.34 Moreover, lower installation costs have led to an increas- ing number of solar projects at airports. The partnership between airports and solar energy is a logical one given their open landscapes, the availability of large surfaces on build- ings and open land to site projects, and the proximity to high-load electricity transmission infrastructure that airports provide. Airport managers have also recognized the business advantages of solar power as a source of alternative revenue and long-term cost savings. In addition, public policy ben- efits to the state, county, and municipal government agencies that manage public airports offer a purposeful basis for these projects, including the opportunity to achieve goals related to greenhouse gas reduction. This increased use of solar energy in and around airports is juxtaposed with the prudent functionality of airports and the primary mission of the FAA to ensure safe and efficient air travel. While early projects demonstrated a strong level of compatibility, recent observations of glare from solar projects have ushered in an increased level of scrutiny and concern. The central question for the FAA when ruling on a proposed solar project is “Will it pose a glare impact?” 3.1.2 What Is Glare? The U.S. Department of Transportation (DOT), FAA, U.S. Air Force (USAF), National Highway Traffic Safety Admin- istration (NHTSA), and other agencies have raised concerns C H A P T E R 3 34Solar Energy Industry Association, “Solar Energy Facts: Q1 2013,” 2013: http:// www.seia.org/sites/default/files/Q1%202013%20SMI%20Fact%20Sheetv3.pdf. CRITICAL RESEARCH NEED—Solar Power Conduct directed studies to increase the knowl- edge base about the potential impacts of glare on airport sensitive receptors and use this new information to improve siting and assessment.

21 over glare from solar energy installations and its impact on pilots, air traffic controllers, and motorists. Glare from direct sunlight has been recognized for many years as a potential hazard for motorists and pilots.35,36,37 Reports citing NHTSA data estimate that solar glare causes nearly 200 fatalities and thousands of accidents involving motor vehicles each year.38 The FAA has reported that glare from direct sunlight contrib- uted to nearly a dozen aviation accidents on average each year during an 11-year study.39 Glare occurs when sunlight causes a temporary visual impairment to an observer. Glare can be produced when looking directly at the sun, including while driving in the direction of the sun after sunrise or sunset, or at any time of day when sunlight is returned to the observer from a reflec- tive surface. Surfaces that produce glare include mirrors, metal roofs, glass, and motionless bodies of water. Smooth, polished surfaces (e.g., glass) cause a specular reflection that is more direct and intense than reflections from rough surfaces, which become diffuse and are less impactful (see Figure 3.1). Although solar photovoltaic (PV) technology is designed to be absorptive of sunlight, it can still produce glare due to its glass surface. Solar power projects with a high con- centration of mirrors pose a greater propensity to produce glare and potential for specular reflection, causing the con- cern that glare could cause a momentary visual impairment to air traffic controllers or pilots depending on the location of the solar project. While most problems related to glare from direct sunlight are predictable, occurring during the mornings and evenings when the sun is close to the horizon (see Figure 3.2), solar glare caused by reflections from solar energy installations can occur at varying times in unexpected locations. Glint (i.e., a momentary flash of light) and glare (i.e., a more continuous source of excessive brightness relative to the ambient lighting) can occur from various solar energy components, such as PV modules, concentrating solar collectors/mirrors, and receivers (Figure 3.3). Impacts of glint and glare on eyesight can include discomfort, disability, veiling effects, after-image effects, and retinal burn.40,41,42,43,44,45,46 Glare affecting aviation receptors can result in after-image effects and veiling (e.g., solar glare on a windshield that might mask pedestrians or vehicles). 35Saur, R., and S. Dobrash, “Duration of Afterimage Disability after Viewing Simulated Sun Reflections,” Applied Optics, Vol. 8, pp. 1799–1801, 1969. 36ABC News, 20/20, “Sun Glare—Sight Unseen,” 1999. 37Nakagawara, V., K. Wood, and R. Montgomery, “Natural Sunlight and Its Association to Aviation Accidents: Frequency and Prevention,” Federal Aviation Administration, Civil Aerospace Medical Institute DOT/FAA/AM-03/6, 2003. 38Costantinou, M., “Glaring Danger—Bright Sun, Deadly Collisions,” San Francisco Examiner, October 12, 1998. 39Ibid. 40Saur and Dobrash, 1969. 41Aslam, T., D. Haider, and I. Murray, “Principles of disability glare measurement: an ophthalmological perspective,” Acta Ophthalmologica Scandinavica, Vol. 85, pp. 354–360, 2007. 42Babizhayev, M., 2003, “Glare disability and driving safety,” Ophthalmic Research, Vol. 35, pp. 19–25. 43Bhise, V., and S. Sethumadhavan, “Effect of Windshield Veiling Glare on Driver Visibility,” Transportation Research Record: Journal of the Transportation Research Board No. 2056, pp. 1–8, 2008. 44Ho, C., C. Ghanbari, and R. Diver, “Methodology to Assess Potential Glint and Glare Hazards From Concentrating Solar Power Plants: Analytical Models and Experimental Validation,” Journal of Solar Energy Engineering—Transactions of the ASME, Vol. 133, 2011. 45Osterhaus, W., “Discomfort glare assessment and prevention for daylight applications in office environments,” Solar Energy, Vol. 79, pp. 140–158, 2005. 46Sliney, D., and B. Freasier, “Evaluation of Optical Radiation Hazards,” Applied Optics, Vol. 12, pp. 1–24, 1973. Figure 3.1. Comparison of reflections—smooth and rough surfaces. Figure 3.2. Highway road sign alerting drivers of potential solar glare.

22 To mitigate these risks, various federal, state, and municipal government codes and regulations seek to prevent harmful glare from solar energy installations.47 Additionally, the FAA recently announced that it would disallow any new solar installations near airports without a quantitative glare analysis, including an assessment of visual impacts. 3.1.3 How Is Glare Characterized? The first significant solar projects at airports began in the early 2000s. The FAA’s approval of the first projects on airport property included questions about glare. These were typi- cally addressed through a qualitative description of solar PV’s absorptive purpose with an occasional field test coordinating with the tower controllers to see what panel reflection might look like. With a first phase of projects built and operational and a growing number of proposals for new projects, the FAA developed “Technical Guidance for Selected Solar Technolo- gies at Airports,” also referred to as “the Solar Guide,” released in November 2010. The Solar Guide was intended to be a central reference for solar PV projects at airports to be used by FAA project reviewers, airports, and industry. It provided relevant information on solar and airports including airspace evaluation issues such as glare. It stated that all solar projects on airport property should submit a Form 7460, “Notice of Proposed Construction or Alteration,” due to potential glare. That chapter also offered options for providing FAA with information on potential glare based on the specific cir- cumstances of the project. These data options were based on methods employed from past projects and included qualitative information, field-testing with a solar panel, and quantitative information generated through computer modeling. In May 2012, a project installed on top of a parking garage at Manchester-Boston Regional Airport generated glare impacts on the air traffic control tower (ATCT), constituting the first reported observation of such glare impacts. In response, the FAA began requiring quantitative modeling for all new solar projects proposed on airport property. In addition, the FAA began working with the Department of Energy (DOE) Sandia National Laboratories to develop a single modeling tool in order to provide high-accuracy predictions of potential impacts on airport sensitive receptors and allow for evaluation of design alternatives to avoid glare impacts. Section 3.1.4 provides details regarding the model developed by Sandia, called the Solar Glare Hazard Analysis Tool (SGHAT). In September 2012, the FAA issued a memorandum entitled “Interim Guidance on Land Uses in the Runway Protection Zone (RPZ)” to provide enhanced clarity on FAA policy. A comprehensive update to the “Airport Design” Advisory Circular (AC 150/5300-13A) was released in September 2012, including a statement that “it is desirable to clear all objects from the RPZ.” It also states that some land uses are conditionally permitted while others are prohibited and that the function of the RPZ is to enhance the protection of people and property on the ground. This is best achieved through airport owner control over RPZs, preferably exercised through the acquisition of suffi- cient property interest in the RPZ and maintaining clearance of RPZ areas from incompatible objects and activities. While the “Object Free Area” specifically prohibits any structures except for frangible items associated with air navigation, the RPZ does not prohibit many land uses but discourages them based on proximity to a potential aircraft mishap. The “Interim Guidance on Land Uses in the RPZ” memo states that certain new or modified land uses in the RPZ require coordination with the FAA APP-400. Included in the list of land uses requiring coordination with APP-400 is “above-ground utility infrastructure (i.e., electrical substations), including any type of solar panel installations.” Prior to coordination with APP-400, ATO Regional Offices and Airport District Offices (ADOs) are directed to work with airport sponsors to identify and document a full range of alternatives that could avoid intro- ducing the land use to the RPZ, minimize the impact of the land use in the RPZ, and mitigate the potential risk to people and property on the ground. The two primary issues associated with siting solar projects in RPZs are (1) the risk to property for the solar facility owner and (2) the risk to aircraft from solar glare. 3.1.4 How Is Glare Managed? Sandia National Laboratories has developed a web-based interactive Solar Glare Hazard Analysis Tool (SGHAT), 47U.S. Department of Energy (DOE), Office of Energy Efficiency & Renewable Energy (EERE), “SunShot Initiative—Examples of Codes that Address Glare from Solar Energy Systems,” 2012: http://www4.eere.energy.gov/solar/sunshot/ resource_center/ask/question/question_11. Figure 3.3. Example of glare viewed from a solar PV facility.

23 which provides a quantified assessment of the following information:48 • Time and place that glare will occur throughout the year for a prescribed solar installation • Potential effects on the human eye at locations where glare occurs • Estimate of the maximum annual energy produced by the solar energy system The SGHAT employs an interactive Google map where the user can quickly locate a site, draw an outline of the proposed PV array, and specify observer locations or paths. It automati- cally records latitude, longitude, and elevation through the Google interface, providing necessary information for sun position and vector calculations. The user also enters addi- tional information regarding the orientation and tilt of the PV panels, reflectance, environment, and ocular factors. SGHAT then employs cone optics to account for beam spreading by integrating both the sun shape and scattering from optical surface errors to produce a cone of reflected sunlight. Rather than using millions of randomly emitted rays employed by ray-tracing methods, it uses a single ray based on the position of the sun at each time-step and orientation of the prescribed array to determine the reflected cone vector and whether glare is visible at prescribed observer locations. If glare is found, the tool calculates the retinal irradiance and subtended angle (or size) of the glare source to predict potential ocular haz- ards, ranging from temporary after-image effects to retinal burn. The results are presented in a simple, easy-to-interpret plot that specifies when glare will occur throughout the year, with color codes indicating the potential ocular hazard. The tool can also predict relative energy production while evalu- ating alternative designs, layouts, and locations to identify configurations that maximize energy production while miti- gating the impacts of glare. Thus, it also serves as a design optimization tool. The FAA is requiring the use of SGHAT to evaluate poten- tial impacts of glare on airport sensitive receptors, which have been identified by ATCT operators and pilots on final approach to landing. The ATCT is particularly at risk because it is a stationary receptor and its exposure to glare is depen- dent on the movement of the sun. Figure 3.4 shows a typical example of when an ATCT may be impacted by glare during 48Ho, C., and C. Sims, “Solar Glare Hazard Analysis Tool (SGHAT) User’s Manual v. 1.0,” SAND2012-10761P, Sandia National Laboratories, Albuquerque, NM, 2012: https://share.sandia.gov/phlux. Figure 3.4. Reflection impacts as the sun rises.

24 One fundamental data source that is currently unavailable is the measurement of reflection from commercially available solar panels. Some manu- facturers advertise the availability of anti-reflecting (A/R) coatings. However, there is little information available to quantify the amount of sunlight reflected. The Sandia National Laboratories conducted solar PV module reflectivity testing as part of this project to improve understanding of the potential for solar panels to produce glare. The total solar reflectivity generally ranged from 6 to 12 percent, while the specular solar reflectivity ranged from approximately 1 to 4 percent. Interestingly, the deep-textured glass sample did not show any measurable specular reflectance, which indicates a significant amount of scattering of the reflected light relative to smooth or lightly textured surfaces. Smooth surfaces, such as mirrors and smooth glass, produce more specular reflections with greater intensity and tighter beams (i.e., larger retinal irradiances and smaller subtended angles), while solar receivers, textured glass, and anti- reflective coatings produce more diffuse reflections with lower solar intensities but greater subtended angles (see Figure 3.5). However, it is important to note that these values are for an incidence angle of 20 degrees. At higher incidence angles, the reflectivity can increase significantly. While these data are not yet ready to be directly applied to the Guidance, it does suggest that use of the deep-textured panels at airports may be a siting option. Reflectivity data is included in Appendix D. ACRP Applied Research—Measuring Reflection Values from Solar Panels Left: smooth float glass; Middle: glass with anti-reflective coating; Right: deeply textured glass Photo credit: Cliff Ho, Sandia National Laboratories; PV samples from Canadian Solar, Inc. Figure 3.5. PV glass samples resulting in different solar glare intensity and size. Research for this Guidebook included a flight crew survey designed and distributed to obtain empirical information from pilots on the sources of their experience with solar glare in general and solar power facilities specifically. Commercial airline and general aviation pilots completed the survey online from October 2012 through July 2013, with 383 total pilots responding. See Appendix E. Thirty-two (32) percent of the respondents operate primarily at airports with known solar energy facilities. Of the pilots who stated that they have experienced solar glare, they noted the following potential sources: 1. Sun at sunrise or sunset—83 percent 2. Bodies of water—57 percent 3. Glass buildings—37 percent 4. Windows—26 percent 5. Building roofs—17 percent When asked how they normally deal with glare, most pilots stated that they adjust shading in the cockpit (83 percent) and use sunglasses (75 percent). Many pilots noted that they attempt to alter their direction of view (48 percent), while others said they wear baseball-style hats, adjust their seat height, or simply use their hands to block the glare. As shown in Figure 3.6, 45 percent of respondents stated that they were aware of solar power facilities at airports at which they operate. While 44 percent were uncertain of the type of technology observed, 31 percent said they observed concentrating solar power (CSP) and 25 percent observed solar photo- voltaic (PV) technology. Nine percent of respondents Developing New Data—Survey of Pilot Experience with Solar Glare

25 who were aware of solar projects indicated that they had experienced glare while 74 percent did not. Of the pilots who did experience glare, 4 percent classified the glare as a “significant nuisance,” 24 percent as a “moderate nuisance,” and 72 percent as “not a nuisance.” When asked whether they consider solar glare to be a safety concern for pilots, 12 percent said “yes,” 45 percent said “no,” 27 percent were “uncertain,” and 15 percent did not respond. Finally, when asked if they had reported a glare problem to authorities, 1 percent responded “yes,” 75 percent said “no,” 5 percent noted some “other” related action, and 18 percent did not respond. These data provide immediate value to practioners in assessing the potential impacts of solar PV projects on pilots. Developing New Data—Survey of Pilot Experience with Solar Glare (Continued) Figure 3.6. Airport photovoltaic panels: awareness and experience. sunrise and how the glare diminishes as the sun rises in the sky. Pilot impacts are more limited because their aircraft is moving and will pass through a glare exposure zone typically in seconds (or tens of seconds) and pilots are also exposed to many sources of glare when in flight and manage the glare with sunglasses, cockpit shades, and other methods. 3.1.5 Case Study: Manchester-Boston Regional Airport In 2012, PV panels at airports received increased atten- tion when glare from a newly installed PV array on a park- ing garage at Manchester-Boston Regional Airport (MHT) had to be covered with a tarp because it caused nuisance glare to air traffic controllers in the nearby control tower (see Figure 3.7).49 After the PV array was installed, Sandia used SGHAT and worked with the FAA and the airport to determine alternative configurations that would mitigate glare to the control tower and approaching flight paths. The team used SGHAT (see Figure 3.8) to evaluate dozens of alternative configurations (e.g., tilt, orientation) and was able to determine a configuration that would mitigate glare while maintaining the desired energy production. Figure 3.9 shows the results of the SGHAT glare analysis for MHT. The dots in the plot represent occurrences of glare 49CNN, “Solar panels cause trouble at airport,” August 31, 2012: http://www. cnn.com/video/standard.html?hpt=hp_t3#/video/bestoftv/2012/09/01/nh-dnt- airport-solar-panels-safety-issues.cnn.

26 as viewed from the user-specified observation point relative to the specified PV array as a function of the time of day and day of the year. The color of the dots indicates the potential ocular hazard, which is impacted by the direct normal irradi- ance (DNI), optical parameters (i.e., reflectance, slope error/ scatter), and ocular parameters (pupil diameter, transmission coefficient, ocular focal length). Figure 3.9 indicates that there is a potential for glare that can cause temporary after-image effect (i.e., a lingering image of the glare in the field of view) during the early morning from January through November. The general spatial and temporal pattern of glare on the PV array was identified using SGHAT Glare Animation Feature and is shown in Figure 3.10. These patterns were verified by observations from the control tower. Photos and videos of glare from the installed PV array at MHT were taken from the ATCT in late April and early May. Figure 3.11 provides a photograph of the glare observed during hours consistent with those predicted by SGHAT. Due to the glare, a tarp was placed over the offend- Date/Time: 7:15AM EST, April 27, 2012 Figure 3.7. Glare viewed from MHT air traffic control tower. Note: PV array (blue outline) and observation point (red marker) entered using drawing tools integrated with Google Maps Figure 3.8. Screen image of MHT glare analysis.

27 ing PV modules and had to be moved every few weeks as the sun position changed. Table 3.1 shows alternative configurations using the same footprint of the PV array that were predicted to produce no glare. The relative annual energy production is also shown for each configuration. In addition, Table 3.1 shows the current PV configuration (200-degree azimuthal angle, 20.6-degree elevation angle) and a maximum energy production configura- tion (180-degree azimuthal angle, 43-degree elevation angle). Based on a review of the glare analyses, an alternative configuration of the PV modules was recommended, rotating the assemblies 90° counter-clockwise to face east-southeast (110 degrees from due north). The tilt of the modules remains the same. This new configuration was re-evaluated using SGHAT to affirm that glare did not affect the flight patterns approaching the runways. Note: All times EST (during EDT, add one hour) Figure 3.9. Glare occurrence and potential for ocular impact in the ATCT. ~June ~March, September ~February, November Figure 3.10. Approximate glare locations on PV array throughout year. Figure 3.11. Glare viewed from MHT ATCT. Note: Photo taken approx. 7:17 AM EST, May 10, 2012; note the tarp placed over some modules

28 3.1.6 Lessons Learned Understanding of the potential impact of solar glare on air- port sensitive receptors has expanded significantly over a short amount of time. When the FAA released the Solar Guide in November 2010, there were very few solar projects at airports and no reports of glare impacts. Glare was assessed primar- ily in a qualitative fashion and the authors recommended the development of modeling tools to better address the issue. Eighteen months later, the glare incident at MHT focused FAA attention on the potential safety concerns and within 6 months, a modeling tool was developed.50 Appropriate use of SGHAT and coordination with the FAA will make siting and impact analysis more efficient and accelerate the approval of future solar projects. Additionally, while low-glare glass may not be an explicit project requirement, research for this Guidebook suggests that airports considering solar projects should request feasibility assessments for use of low-glare glass to mitigate glare in Requests for Proposals (i.e., bid solicitation). 3.2 Wind Power 3.2.1 Research Context Since 2000, wind generation capacity in the United States has increased from 5 GW to 43 GW, and wind could supply 20 percent of the nation’s electricity by 2030, equating to Azimuthal Angle (degrees) Elevation Angle (degrees) Relative Annual Energy Production 180 43 100.0%1 200 20.6 93.9%2 120 40 88.9% 120 50 87.2% 110 20.6 82.4% 110 30 85.0% 110 40 84.7% 120 60 83.7% 110 50 82.8% 130 70 81.5% 100 30 80.9% 100 20 80.8% 100 40 79.9% 110 60 79.3% 120 70 78.3% 100 50 77.6% 90 20 77.5% 210 80 76.9% 90 30 76.4% 220 80 75.8% 90 40 74.5% 110 70 74.2% 100 60 74.1% 130 80 74.0% 90 50 71.8% 120 80 71.3% 100 70 69.2% 90 60 68.1% 110 80 67.7% 90 70 63.4% 100 80 63.2% 90 80 57.8% Notes: As predicted to produce no glare from perspective of air traffic control tower; azimuthal angle measured clockwise from due north (0°); elevation angle measured from 0° (facing up) to 90° (facing horizontal) 1. Maximum energy production; produces glare to air traffic control tower 2. Current configuration; produces glare to air traffic control tower Table 3.1. Alternative no-glare PV array configurations. 50Ho and Sims, 2012.

29 300 GW (including 54 GW of offshore wind), as shown in Figure 3.12.51,52 A variety of incentives have catalyzed wind power growth, including tax credits, purchasing mandates by federal agen- cies, and state-level renewable energy portfolio standards (RPS).55 Examples include the DOE goal of 20 percent by the year 2030,56 the Department of Defense (DoD) goal of 25 percent by 2025,57 and the 2004 Colorado initiative whereby Colorado became the first state to pass an RPS. Approximately one-half of all states have followed suit with RPS development, ensuring a growing role for wind energy production.58 Wind Turbine Generators (WTGs) have the potential to cause a variety of negative effects on aviation activities. Results from studies done in the United States and Europe have shown that these physical and electromagnetic effects directly affect operational missions conducted by government agencies. Radar systems in particular suffer serious negative effects, although other systems such as communications systems, navigation systems, and even aircraft on runways or approaches are also impacted as well. 3.2.2 What Are the Impacts of Wind Power? Most contemporary wind turbines are constructed with a three-bladed rotor connected to a generator set atop a 51DOE, Office of Energy Efficiency and Renewable Energy (EERE), “20% Wind Energy by 2030, Increasing Wind Energy’s Contribution to U.S. Electricity Supply,” DOE/GO-102008-2567, July 2008: http://www.osti.gov/bridge. 52DOE, “A National Offshore Wind Strategy: Creating an Offshore Wind Energy Industry in the United States,” February 2011. 53DOE, EERE, “20% Wind Energy by 2030, Increasing Wind Energy’s Contribution to U.S. Electricity Supply,” DOE/GO-102008-2567, July 2008: http://www.osti. gov/bridge. 54DOE, “Interagency Field Test & Evaluation, Government Listening Session Overview,” presentation by Jose Zayas, AWEA WindPower 2013 Conference and Exhibition, May 7, 2013. 55DOE, EERE, “20% Wind Energy by 2030, Increasing Wind Energy’s Contribution to U.S. Electricity Supply,” DOE/GO-102008-2567, July 2008: http://www.osti. gov/bridge. 56Ibid. 57DOE, EERE Federal Energy Management Program, “Large-Scale Renewable Energy Guide, Developing Renewable Energy Projects Larger Than 10 MWs at Federal Facilities,” DOE/GO-102013-3915, March 2013: http://www1.eere. energy.gov/femp/. CRITICAL RESEARCH NEED—Wind Power Develop a synthesis of aviation safety risk factors related to wind technology to inform siting and operations guidance, including radar interference, wake effects, and MET obstructions. 58Wind Energy Association, Monthly Newsletter, March 14, 2013. Figure 3.12. Cumulative installed wind power capacity through 2030.53,54

30 monopole tower (see Figure 3.13). The increased capacity over the past 10 years has been primarily achieved by building the towers taller to catch a more consistent wind resource (see Figure 3.14). Current wind turbines have a blade tip height of as much as 500 ft. above ground level (AGL) and heights may continue to increase. Given that defined airspace technically begins at 200 ft. AGL, most wind turbines constructed in the United States have an impact on aviation. Additionally, the NAS consists of more than 23,000 ATC facilities, airports, and NAVAIDs, hundreds of which are located in areas where wind developers would like to build.59 The material related to wind power in this Guidebook is intended to address aviation safety issues related to WTGs near airports and ATC facilities. The impacts of wind turbines on airports and airspace include physical penetration, com- munications systems interference, and rotor blade turbulence, discussed in detail in the following sections. WTG develop- ers should be aware of electromagnetic systems and airspace activities and address the potential project implications early in the planning process, especially those related to FAR Part 77 navigable airspace restrictions. 3.2.2.1 Physical Penetration Structures that produce a physical penetration to air- space are the simplest to understand. Any structure rising over 200 ft. AGL penetrates the NAS, triggering the require- ment for airspace review under FAR Part 77 to determine whether or not the structure creates an airspace hazard. Tall structures located proximate to airports and ATC facil- ities (e.g., radar) are more likely to produce a potential airspace concern beyond physical impingement. Further- more, airspace reviews examine individual structures, so cumulative effects of many structures may be more diffi- cult to evaluate. Physical penetration is also an important issue for meteorological test towers, which are deployed to measure wind resources in advance of project development (see Section 3.2.4). 3.2.2.2 Radar A radar system consists of four major components: (1) a transmitter, (2) a directional antenna, (3) a receiver that pro- cesses incoming data, and (4) a display for the operators. The core concept of radar requires the transmission of energy pulses from the antenna in a known direction and a “target” that reflects some amount of that energy (i.e., a “return”) back to the antenna where it is received and processed before it is displayed on an operator’s panel as a target. The time the energy takes from initial antenna pulse to the time it is received provides the distance or “range” to the target. The size of the target is determined by the strength of the return, which is a function of the radar cross section (RCS) of the target. Targets with more reflective materials and/or surfaces have a larger RCS. The larger the RCS, the easier it is to distinguish a target from surrounding “clutter.” Clutter is everything else the radar sees (e.g., terrain features, birds, bats, insects, weather phenomenon for non-weather radars, and aircraft for weather radars). Radar designers use an array of methods to eliminate clutter so that the target in question stands out. A variety of amplitude threshold techniques pro- vides engineers an array of tools they can use to eliminate clutter (e.g., Plot Amplitude Thresholds [PAT], Range Azimuth Gates [RAG], etc.). Some radars use multiple stacked beams to allow operators to determine an altitude. In addition to signal strengths, radar designers can use Doppler frequency shift techniques as a way to see and esti- mate the speed of moving targets, which indicate a “zero” Doppler. This proves useful in eliminating stationary targets (e.g., buildings or terrain) from a radar image. Another way to determine whether a target is moving is to utilize periodic scanning techniques to “take snapshots” of the surveillance area and then compare them to see if a target has moved. This is typically accomplished using rotating antennas or by using phased arrays that focus on smaller areas on a reoccurring basis in order to produce those snapshots. Many other methods exist as well.59FAA, “Instrument Procedures Handbook,” FAA-H-8261-1A, 2007. Figure 3.13. Terminology associated with wind turbine generators (WTGs).

31 Radars used for weather employ many of the same general techniques as radars used to detect aircraft. The key difference between them is that the primary objective of weather radar is to measure air density (relating to moisture content) and air mass movements (i.e., winds aloft). These measurements are then translated via weather-based processors to operator displays that meteorologists use to determine weather patterns and provide forecasts. Examples of affected/suspected radar systems include: • Long-Range Surveillance Systems (ARSR-1 to 4, CARSR, FPS-117, etc.) • Terminal Systems (ASR-7, 8, 9, 11, etc.) • Weather Systems (WSR-88D, TDWR, etc.) • Marine Systems (CODAR, WERA, etc.) • Other Key Systems (OTHR, Airborne Systems such as TARS, AWACS, etc.) WTGs pose particular challenges to radar due to a wide range of variables that include the following: tip speeds over 225 mph (Doppler issue), blade lengths exceeding 50 m long (size), and radar cross sections measuring 30–40 dB relative to 1 square meter (dBsm), also known as clutter.60 When a developer places tens or hundreds of WTGs in a wind farm, and several wind farms are sited around a single radar site, the capability of that radar may be impacted to the point that the cumulative effects can render the radar ineffective. As indicated by Figure 3.15, WTGs affect radar systems in a number of ways, reducing their effectiveness to support federal, state, and local activities and missions. The three pri- mary electromagnetic impacts on radars are as follows:61 1. Decreased Sensitivity (PD) 2. False Targets (PFA) 3. Corrupted Track Quality Investigators measure these primary impacts to determine the broader effects on air and weather surveillance missions. In effect, the extent to which particular radar is impacted in these three ways will likely determine whether an objection is raised to any particular wind energy project. Reviewing agencies and authorities assess the impacts of WTGs on radar differently depending on their core missions. For example, the FAA assesses radar impacts to ensure flight safety, aircraft separation, and other factors related to airspace operations. Other agencies and authorities are listed below with their radar-related concerns: • Weather Reporting and Prediction—Storm and rainfall prediction, tornado warning, etc. • Homeland Security—Border protection, law enforce- ment, drug interdiction, etc. 60DOE, “Interagency Field Test & Evaluation, Government Listening Session Overview,” presentation by Jose Zayas, AWEA WindPower 2013 Conference and Exhibition, May 7, 2013. 61Ibid. Figure 3.14. Increase in size of WTGs over time.

32 • Homeland Defense—Aerospace warning/control, air defense, support to law enforcement, etc. • Military Training—Potential for degradation of perfor- mance of air traffic control and other radars used during flight training • Research, Development, Test and Evaluation—Develop- mental and operational testing, and system certification • Maritime Patrol—Coastal navigation, waterway safety, and search and rescue • Law Enforcement—Collateral effects/chain-of-custody for local, state, federal, and tribal agencies • Critical Infrastructure Protection—Nuclear security operations, continuity of government, etc. 3.2.2.3 Rotor Wake Turbulence ACRP Synthesis 28 provides a description of rotor-induced turbulence: “Wind turbines disrupt uniform air flow caus- ing unseen turbulence produced downstream of wind tur- bines.” Additionally, ACRP Synthesis 28 points out that, “Turbulence associated with wind turbines is less an issue of predictability, as the turbulence potential can be visualized by the presence of the wind turbines and whether or not they are spinning.” The issue is more about understanding the distance that rotor-induced turbulence may occur from a wind turbine and what the degree of turbulence might be compared with other sources of existing natural and fabricated turbulence. Figure 3.16 illustrates the effects of rotor wake turbulence. Based on a review of the issue, concern about turbulence impacts is primarily limited to GA aircraft due to their light- weight airframes and propensity to operate at lower altitudes where turbulence would occur (see Figure 3.17). Aviation Figure 3.15. WTGs as physical obstructions to radar signals. Figure 3.16. Fog trailing from Horns Rev offshore wind farm, Denmark.62 62Vattenfall Energy, Christian Steiness, Sweden, 2007.

33 constituents have raised safety concerns about performing services near wind turbines due to potential impacts of tur- bulence including air ambulance63 and crop spraying.63,65,66 There have also been reports from recreational pilots about detecting turbulence downwind from operating wind turbines. Several studies offer guidance in determining the safest dis- tance for aircraft to travel downwind of a wind turbine: • IFT&E Pilot Reports:67 During the Interagency Field Test and Evaluation (IFT&E) Program flight campaigns, Cessna 182s were flown as low as 500 ft. above WTGs with little to no effects. When pilots did experience heavy turbulence, their interpretations were that the rising terrain leading up to the turbines exacerbated the turbulence effects and may have been noticeable without the presence of WTGs. In another situation, a light jet aircraft pilot reported he had flown approximately 1,000 ft. behind a wind farm and slightly below rotor tops where the turbines were located on a ridge and experienced turbulence so bad that “he’d never knowingly do it again.” Finally, an Ultralight pilot stated he also noted turbulence as he made circuitous flights around wind farms on ridges and he purposefully chose “not to fly on the windier days,” partially because he thought that turbulence above was an even bigger concern for his size aircraft. • Modeling Impacts on a Cheetah Rotax 582 Ultralight:69 A South African study modeled turbulence impacts from utility-scale wind turbines on an Ultralight aircraft (see Figure 3.18) during approach and take-off using compu- tational fluid dynamics (CFD) analysis. It concluded that a minimum safety zone is 5 rotor diameters, though a safety factor should be applied, which would result in a safety zone of 10 to 15 rotor diameters. • Various Studies have shown that wake effects from a wind farm wake are approximately 20 km independent of the size of the wind farm as well as background meteorology.70 Measurements at 16 rotor diameters downstream of the wind turbine indicate that turbulence effects are still noticeable.71 Near-field wake turbulence behind a horizontal axis turbine extends downstream to 3 to 7 blade diameters.72 Turbine separation in wind farm clusters is 6 to 7 diam- eters in the direction of the prevailing wind direction and 3 diameters perpendicular to the prevailing conditions. The disruption to wind velocity occurs even at 16 times the blade diameter. This is largely due to the extraction of power from the airstream, and the time it takes the airstream to recover back to the free-airflow. Therefore, it may be necessary to require separation beyond 16 blade diameters.73 Figure 3.17. Aerial spray aircraft. 63Multi-Municipal Wind Turbine Working Group, “Letter to the Honourable Deb Mathews, Minister of Health, Toronto, Ontario,” sent by elected officials and appointed citizens of Bruce, Grey, Dufferin, Huron, and Perth Counties, Ontario, Canada, May 29, 2012. 64Calleja, J., “Wisconsin Applicator Declares Towers Off Limits for Spraying,” Agri- cultural Aviation, National Agricultural Aviation Association (NAAA), November/ December 2009: http://www.agaviation.org/sites/default/files/ReabeLetter.pdf. 65Hunter, A., “Wind Turbines and Aerial Application,” Fly Low, Fly Safe, Vol. 2, Issue 4, Fall 2011: http://www.nationair.com/pdf/FlyLowFlySafe_Fall10.pdf. 66Boorowa District Landscape Guardians, “Wind Turbines and Aviation”: http://www.bdlg.org/BDLG%20Brochures/Aviation.pdf. Accessed January 30, 2014. 67Interagency Field Test and Evaluation Program (IFT&E), Discussions with Pilots, April 2013. Figure 3.18. Cheetah Rotax from Rainbow Aircraft.68 68Cheetah, Photo of Rainbow Aircraft, 2011: http://www.aerotrike.co.za/cheetah/ index.html. 69Verbeke, J., “The Influence of wind turbine induced turbulence on Ultralight aircraft,” KHBO Institute for Fluid Dynamics, Academic Year 2010–2011, Oostende, Belgium. 70Baidya Roy, S., “Simulating impacts of wind farms on local hydrometeorology,” Aerodyn, 2011. 71Vermeer, L. et al., “Wind turbine wake aerodynamics,” Progress in Aerospace Sciences, Vol. 39, pp. 467–510, 2003. 72Holland, R., “Wind turbines Wake Turbulence and Separation”: http://www. arising.com.au/aviation/windturbines/wind-turbine.html. 73Medici, D., “Wind Turbine Wakes—Control and Vortex Shedding,” KTH Mechanics Royal Institute, 2004: http://www.diva-portal.org/smash/get/diva2: 9439/FULLTEXT01.pdf.

34 Both the FAA74,75,76 and United Kingdom (UK) Civil Aviation Authority (CAA)77,78 have directives that establish separation criteria due to the danger of wake turbulence on departing/arriving aircraft as well as recommendations for avoiding airborne turbulence below and downwind from aircraft, especially larger aircraft. Chapter 7 of the FAA Aeronautical Information Manual (AIM) provides the following description of wake vortex characteristics in Section 3, “Wake Turbulence”: • The vortex circulation is outward, upward and around the wing tips when viewed from either ahead or behind the air- craft. Tests with large aircraft have shown that the vortices remain spaced a bit less than a wingspan apart, drifting with the wind, at altitudes greater than a wingspan from the ground. In view of this, if persistent vortex turbulence is encountered, a slight change of altitude and lateral position (preferably upwind) will provide a flight path clear of the turbulence. • Flight tests have shown that the vortices from larger (transport category) aircraft sink at a rate of several hundred feet per minute, slowing their descent and diminishing in strength with time and distance behind the generating aircraft. Atmospheric turbulence hastens breakup. • When the vortices of larger aircraft sink close to the ground (within 100 to 200 ft.), they tend to move laterally over the ground at a speed of 2 or 3 knots. • There is a small segment of the aviation community that have become convinced that wake vortices may “bounce” up to twice their nominal steady state height. With a 200-ft. span aircraft, the bounce height could reach approximately 200 ft. AGL. This conviction is based on a single unsubstanti- ated report of an apparent coherent vortical flow that was seen in the volume scan of a research sensor. No one has determined the conditions that cause vortex bouncing, how high wake vortices bounce, at which angle they bounce, or how many times they may bounce. On the other hand, no one has determined in certain terms that vortices never bounce. Test data have shown that vortices can rise with the air mass in which they are embedded. Wind shear, particu- larly, can cause vortex flow field “tilting.” In addition, ambient thermal lifting and orographic effects (rising terrain or tree lines) can cause a vortex flow field to rise. • A crosswind will decrease the lateral movement of the upwind vortex and increase the movement of the downwind vortex. Thus, a light wind with a cross-runway component of 1 to 5 knots could result in the upwind vortex remaining in the touchdown zone for a period of time and hasten the drift of the downwind vortex toward another runway. To put this into perspective, the FAA ATC is required to provide 2-minute separation of aircraft taking off and land- ing to avoid wake turbulence, reflecting its treatment as a severe danger to aircraft. 3.2.3 Characterizing and Managing Impacts 3.2.3.1 Radar DOE recently collaborated with the DoD, DHS, and FAA in sponsoring the IFT&E Program to validate commercial off-the-shelf (COTS) technologies with the potential to mitigate electromagnetic interference from WTGs on radar systems.79 The IFT&E Program Team formed in June 2011 and operated through approximately October 2013, led by the Sandia National Laboratories (for expertise in wind energy deployment) and the Massachusetts Institute of Technology (MIT) Lincoln Laboratory (for expertise in radar technology analysis). Additionally, though not a primary partner, the National Oceanic and Atmospheric Administration (NOAA) provided weather data and aircraft support. The three stated goals of the IFT&E Program are as follows:80 1. Characterize the impact of wind turbines on existing Air Surveillance Radars. 2. Assess near-term mitigation capabilities proposed by industry. 3. Collect data and increase technical understanding of interference issues to advance development of long-term mitigation strategies to determine future R&D priorities. The IFT&E Program consisted of three 2-week flight cam- paigns near NAS radar systems in high-density WTG areas in Minnesota and Texas. In addition, nine private sector vendors that were selected by Sandia National Laboratories participated in the flight campaigns to test and evaluate can- didate technologies. In each of the campaigns, MIT Lincoln Labs built an Adjunct Radar Analysis Processor (ARAP) that was reused (with modifications) at each test event to collect 74FAA, “Aeronautical Information Manual”: http://www.faa.gov/air_traffic/ publications/atpubs/aim/index.htm. 75FAA, “Pilot and Air Traffic Controller Guide to Wake Turbulence,” April 1995. 76FAA, Order JO 7110.65U, “Air Traffic Control Section 9, Departure Procedures and Separation (with Changes),” February 9, 2012. 77UK Civil Aviation Authority (CAA), “Safety Sense Leaflet,” January 2009: http://www.caa.co.uk/publications 78CAA, “NATS Aeronautical Information Circular (AIC),” P 18/2009, 26 March 2009: http://www.nats-uk.ead-it.com/public/index.php.html. 79IFT&E, “Interagency Field Test and Evaluation of Wind-Radar Mitigation Technologies—Summary,” June 28, 2012. 80DOE, “Fact Sheets on the First and Second Test Results of the Interagency Field Test & Evaluation of Wind—Radar Mitigation Technologies,” October 31, 2012, and April 30, 2013.

35 detailed data from the federally owned NAS radar systems.81 Sandia National Laboratories worked with participants from the wind energy industry to track weather conditions and gather data from WTGs in the test area, including individual turbine circumstances (e.g., rotation rate, blade angle, nacelle direction) as well as static turbine specifications before and during the tests. Multiple types of government and private aircraft were flown at each test event, using a GPS tracker to establish positional accuracy data. In order to preserve cred- ibility across the field stakeholders, no flight information (e.g., aircraft type, speed, route, etc.) was provided to NAS radar operators or technology vendors. All three flight campaigns were completed by the publication of this Guidebook but data analysis was completed for only the first two campaigns. Once the IFT&E Program Team finalizes the data analysis and reports for all three tests, results will be distributed to the sponsoring federal agencies. The individual test results and associated recommendations are expected to achieve the following objectives:82 • Accelerate the adoption of mitigation technologies by the radar community. • Allow the sponsor agencies to make near-term and future investment decisions. • Provide government agencies quantitative WTG interference data that can be used by government researchers to develop new mitigation technologies. • Provide additional insights and a deeper scientific under- standing into the phenomenology of wind turbine inter- ference on radar systems for all stakeholders. • Encourage participants to use their proprietary information garnered during the tests for product improvements. 3.2.3.2 Turbulence Beyond siting guidance that can be extracted from field and modeling studies summarized in Section 3.2.2.3, a tur- bulence modeling tool developed by the Fraunhofer Institute for Wind Energy and Energy System (i.e., Simulation of Wind Farm Effects on Light Aircraft) may be helpful in evaluating the potential effects of projects sited near airports and aircraft activity areas.83 The model is reported to compute how wind power plants influence aircraft at various wind speeds and wind directions. The model allows users to input a variety of turbine parameters and evaluate the effects of two differ- ent wind speeds and up to five aircraft flight trajectories. The Fraunhofer simulation, shown in Figure 3.19, demonstrates the turbulence generated by wind turbines. The red area shows heavy turbulence, which is common near wind farms. In the area of research, a new WTG turbulence study was commissioned in July 2013, conducted jointly by Sandia National Laboratories and Texas Tech University Scaled Wind Farm Technology Facility, located at the Reese Technology Cen- ter in Lubbock, TX. It is expected to provide a wide array of “research opportunities for [the] study of turbine-to-turbine interactions”84 and to provide the most detailed studies avail- able on complex wind farm aerodynamics. Sandia has devel- oped an innovative LIDAR-based system that will be able to gather turbulence data in large volume spaces. Due to its prox- imity to Reese Air Force Base, this facility may also be useful in studying the effects of WTG turbulence on aircraft. 3.2.3.3 Agency Siting Guidance As noted in the American Wind Energy Association (AWEA) Siting Guide, “Consultation with a number of federal agencies 81DOE, “Fact Sheets on the First and Second Test Results of the Interagency Field Test & Evaluation of Wind—Radar Mitigation Technologies,” October 31, 2012 and April 30, 2013. 82IFT&E, “Interagency Field Test and Evaluation of Wind-Radar Mitigation Technologies—Summary,” June 28, 2012. 83Pele, Anne-Francoise, “Simulations show pilots should steer clear of wind farms,” 2012: http://www.eetimes.com/electronics-blogs/other/4395549/Simulating- wind-farm-risks-for-ultra-light-aircrafts. 84Barone, M. and J. White, “Scaled Wind Farm Technology Facility: Research Opportunities for Study of Turbine-Turbine Interaction,” Sandia National Lab- oratories, SAND2011-6522. Figure 3.19. Fraunhofer simulation graphic.

36 that have jurisdiction over radar systems is often part of obtaining regulatory approvals. As part of its hazard deter- mination . . . the FAA engages other agencies to review a project that has filed an NPC (Notice of Proposed Con- struction)”.85 Key agencies of interest here include DoD, DHS, the National Telecommunications and Information Administration (NTIA) Interdepartment Radio Advisory Committee (IRAC), and NOAA. The AWEA Siting Guide specifically notes that if a project is to be sited near an area of concern, “a developer is advised to contact the DoD Siting Clearinghouse in order to de-conflict early in the planning process. The DoD Siting Clearinghouse provides a ‘one-stop shop’ for comprehensive, expedited evaluation of energy projects and their potential effect on DoD operations. The Clearinghouse’s formal review process applies to projects filed with the Secretary of Transportation, under Title 49 USC Section 44718 (pertaining to the FAA’s obstruction evaluation process), as well as other projects proposed for construction within military training routes or special use airspace, whether on private, state, or federal property (e.g., land managed by the Bureau of Land Manage- ment [BLM].” The DoD Siting Clearinghouse mission is to protect DoD mission capabilities from incompatible devel- opment by collaborating with DoD Components and exter- nal stakeholders to prevent, minimize, or mitigate adverse impacts on military operations, readiness, and testing. The DoD Siting Clearinghouse acts as the conduit between the FAA’s Obstruction Evaluation Review Process and the wind developer. Operational impacts of wind turbines on DoD missions are determined in parallel by several DoD organiza- tions using differing methods and multiple modeling tools, none of which are available for public view. DoD has collaborated with the Natural Resources Defense Council (NRDC) to publish a guide for working with the DoD on siting renewable energy development.86 The goal of the primer is to identify key considerations for siting renewable energy projects that could affect military operations. Addi- tionally, the DoD Office of Economic Adjustment, through the Defense Economic Adjustment Program, provides both tech- nical and financial assistance to state and local governments through the Joint Land Use Study (JLUS) process87 to col- laborate with the local military to plan and carry out strategies promoting compatible civilian use adjacent to installations, ranges, military training corridors, and special use airspace. This community-driven, cooperative planning process results in a strategic plan and specific implementation actions to ensure that civilian growth and development are compatible with vital training, testing, and other military operations. The JLUS process promotes and enhances civilian and military communication and collaboration, serves as a catalyst to sustain the military mission, and promotes public health, safety, quality of life, and economic viability of a region. Finally, the DoD Readiness and Environmental Protection Integration (REPI) Program88 assists identification of innovative land conserva- tion solutions that protect and benefit military readiness and sensitive environmental habitats, while promoting feasible alternatives to otherwise intractable wind turbine generation development near military installations, special use airspace, and military training routes. 3.2.4 Meteorological Evaluation Towers Meteorological Evaluations Towers (METs) also present unique challenges to aviation. Wind power developers erect METs during project siting to investigate the viability of phys- ical land areas to support a commercial wind project. METs record the on-site wind speed, typically for at least 1 year, and the data is then assessed to predict how much electricity the project site could support. The towers utilize anemometers (i.e., wind sensors) at several different heights above ground level to evaluate the wind resource. Taller towers provide more accurate data for evaluating wind at the height of the rotor, which can be 300 to 400 ft. AGL, but shorter towers are more cost effective in the preliminary project stages. Wind developers often erect towers at heights below 200 ft. in order to avoid filing a Form 7460 application with the FAA, which also prevents their competitors from easily identifying potential project locations and allows them complete flexibility over the process without FAA regulation. Further complicating the issue, wind farm sites are often in rural areas that are regu- larly used by small aircraft, which may be flying at low altitude. In addition to recreational pilots, businesses and public ser- vice providers may be operating aircraft at low altitudes and at risk of collision with METs, including agriculture appli- cators, aerial fire suppression, helicopter emergency medical services, animal damage control operations, fish and wildlife surveys, and law enforcement operations. Figure 3.20, courtesy of the National Agricultural Aviation Association (NAAA), shows a 198-ft. tall MET located within the wind farm. In this case, the wind turbines are visible to pilots, but prior to construction, the MET stood alone on the landscape and would have been difficult to detect in isolation. 85American Wind Energy Association (AWEA), “Wind Energy Siting Handbook,” Para 4.1.6, pp. 4-20 to 4-22, February 2008. 86U.S. Department of Defense (DoD), National Resources Defense Council (NRDC), “Working with the Department of Defense: Siting Renewable Energy Development,” September 2013: http://www.acq.osd.mil/dodsc/library/Siting_ Renewable_Energy_Primer_5SEP13_FINAL_WEB.pdf. 87DoD, Office of Economic Adjustment (OEA), “About Compatible Use: Joint Land Use Study—JLUS”: http://www.oea.gov/programs/compatible-use/about. 88DoD, Readiness and Environmental Protection Integration (REPI), Program Website: http://www.repi.mil/.

37 When METs are erected at heights below 200 ft. AGL, they are not painted or lit in a manner that can be seen easily by pilots. In fact, the towers are narrow, unmarked, and grey in color, making them very difficult to see in day and invisible at night. While FAA regulations related to marking of such structures are undefined, this aviation safety problem has been identified in other countries, including Canada and the United Kingdom. • UK CAA—Civil Aviation Publication (CAP) 764, “CAA Policy and Guidelines on Wind Turbines” states that wind power developers “be aware that anemometer masts are often difficult for pilots to acquire visually, and so aviation stake- holders may assess that individual masts should be consid- ered a significant hazard to air navigation and may request (either during the planning process, or post-installation) that masts be lit and/or marked.” 89 • Transport Canada—Advisory Circular No. 600-001, “Mark- ing of Meteorological Towers,” states, “it is not feasible for Transport Canada to regulate the application of marking and lighting of all objects that might be encountered by pilots who choose to engage in a specialized activity that involves flight very low to the ground. Most of these objects are of natural origin (e.g., trees). The MET, however, is a structure that is under the control of the wind farm com- pany. In as much as there is control, it would seem both reasonable and prudent to apply marking because of the adverse impact the tower may have upon the known activ- ity of crop spraying. Here we are considering only mark- ing, since crop spraying does not occur at night.90 In the United States, the National Transportation Safety Board (NTSB) recently issued a safety recommendation regarding METs in a letter dated May 15, 2013.91 The letter recommended that the Department of Agriculture (USDA), Department of Interior (DOI), and DoD provide or direct applicants for METs on federal lands to information contained in FAA AC 70/7460-1, “Obstruction Marking and Lighting.” The NTSB also included safety recommendations to the FAA, AWEA, and all 50 state governments and the District of Columbia to advise applicants in a similar manner. It recommends that the FAA establish MET lighting requirements92 and develop a national MET database. The NTSB proposes that the AWEA revise its handbook to clearly indicate the hazards that METs pose to low-altitude operations and encourage marking them to improve visibility. It also proposes that states, District of Columbia, Puerto Rico, Northern Mariana Islands, Samoa, and the Virgin Islands should enact legislation requiring that METs be marked and registered in a directory. Finally, the NTSB sent letters asking other stakeholders to take an active role in educating wind energy developers on the dangers METs pose, enacting legislation, and marking/lighting METs. The NTSB’s actions suggest that a 2011 FAA policy statement93 recommending that METs be marked is not strong enough.94 In issuing the safety recommendations, the NTSB concludes that, “due to their rapid construction and lack of conspicu- ity, METs pose a threat to pilots who conduct low-altitude operations and that the required registration, marking, and— where feasible—lighting of these structures would aid pilots in avoiding them.” It also pointed out that the lack of federal requirements has led 10 states to take action on the threat to aviation safety of METs as short as 50 ft. AGL. Four states (Montana, Nebraska, North Dakota, and Wyoming) require all MET locations to be registered and the towers marked. Five states (California, Idaho, Kansas, Mississippi, and South Dakota) require that METs be clearly marked. 3.2.5 Offshore Wind While there are currently no wind turbines constructed in U.S. waters, offshore wind farm development is expected over the next 5 to 10 years. The first offshore wind farm was constructed in Danish waters in 1991 and currently there are over a 1,000 wind turbines operating in marine waters in 89CAA, “CAP 764, CAA Policy and Guidelines on Wind Turbines,” Chapter 2, paragraph 10.3, p. 9, July 2011. 90Transport Canada, Advisory Circular No. 600-001, “Marking of Meteoro- logical Towers,” March 3, 2011: http://www.tc.gc.ca/eng/civilaviation/opssvs/ managementservices-referencecentre-acs-600-600-001-1276.htm. Figure 3.20. 198-foot MET within a wind farm array. 91National Transportation Safety Board (NTSB), “Safety Recommendation Letter to the FAA,” Sections A-13-16 and A-13-17, May 15, 2013. 92Spence, Charles, “NTSB wants meteorological towers marked,” General Aviation News, 23 May 2013: http://www.generalaviationnews.com/2013/05/ntsb-wants- meteorological-towers-marked/. 93Federal Register, Vol. 76, No. 3, “Proposed Revision to FAA Advisory Cir- cular on Marking Meteorological Evaluation Towers,” pp. 490–491, FR Doc No. 2010-33310, January 5, 2011. 94NTSB, “Safety Recommendation Letter to the FAA,” May 15, 2013.

38 • December 15, 2003—An Erickson SHA Glasair TD aircraft collided with an unmarked and unlighted MET during VMC conditions near Vansycle, Oregon. The aircraft was destroyed and both occupants sustained fatal injuries. • May 19, 2005—An Air Tractor AT-602 agricultural airplane was destroyed upon impact with terrain after a collision with an unmarked and unlighted MET (originally recorded as an antenna tower, but later revised) near Ralls, Texas, fatally injuring the pilot in VMC conditions. • January 5, 2011—The FAA published a notice seeking comments on a proposed revision to AC 70/7460-1, “Obstruction Marking and Lighting,” requesting comment on the establishment of “a uniform and consistent scheme for voluntarily marking” METs less than 200 ft. AGL. • January 10, 2011—A Rockwell International S-2R agricultural aircraft was severely damaged and the pilot fatally injured after it struck an unmarked and unlighted MET in VMC conditions on Webb Tract Island, Oakley, California. • March 6, 2011—The NTSB issued a Safety Alert (SA-016) on METs, urging pilots to be vigilant around them. The Safety Alert also provided background information on accidents, the status on regulatory policy, and encouraged the marking of METs. • June 24, 2011—The FAA published a policy state- ment with its recommendation for the voluntary marking of METs erected in remote and rural areas that are less than 200 ft. AGL and that land- owners and developers use guidance contained in Advisory Circular 70/7460-1, “Obstruction Marking and Lighting” for such voluntary marking. It stated that lighting is not necessary because agricultural operations are performed during daylight. It also stated that it is infeasible for the FAA to maintain a national database for structures that are less than 200 ft. AGL. • August 27, 2012—California Gov. Jerry Brown signed legislation requiring towers “standing 50 feet and taller to be clearly marked with bright aviation colors.” The new rules will apply to towers built after January 1, 2013 and will “sunset” in five years. • May 15, 2013—The NTSB issued a “Recommenda- tion Letter” (described previously) to the FAA. Timeline for Regulation of METs Europe and China. It is important to understand the poten- tial impacts of this construction on airports and aviation. Experience in Europe offers some guidance for evaluating issues in the United States. The potential issues identified in the United Kingdom are similar to those on land-based wind turbines: Obstacle Avoidance (e.g., WTGs, METs); Electromagnetic Interference (e.g., radars, NAVAIDs, communications systems); WTG- Induced Wake Turbulence; and the government missions that these concerns affect (e.g., aviation safety, unimpeded air surveillance for national security). Given the geographic nature of the British Isles, helicopter routes have been in use in the North Sea and Morecambe Bay for many years and guidance recommends against siting offshore wind turbines within 2 nautical miles (NM) of any helicopter main route (HMR). Helicopter traffic has also been common in support of building and maintaining offshore oil platforms and guid- ance states that installations within 9 NM of such a platform can pose an aviation safety risk. DoD works with the Bureau of Ocean Energy Management (BOEM) to ensure that offshore wind resource development is compatible with military training, testing, and operations on the Outer Continental Shelf. BOEM and DoD are work- ing collaboratively with other federal agencies and state gov- ernments to plan for low-conflict offshore renewable energy development. The Cape Wind Project located south of Cape Cod, Massachusetts, offers some insight into the application of FAA review processes for an offshore wind project. Cape Wind obtained a determination of no hazard from the FAA in August 2012, which included four conditions: (1) a require- ment of notice of construction beginning, (2) a $15M escrow to replace an upgraded radar (after a study indicated an unacceptable level of performance) if it did not fully miti- gate the interference/clutter issue, and (3 and 4) two light- ing and marking conditions (temporary and permanent). Three particularly remarkable items a developer should notice in reviewing the full text of this study include the following: • The general note stating that, “A Probability of Detec- tion (PD) of 0.9 (90%) or better is desirable. For most

39 search radars, a PD of 0.8 (80%) or better is considered satisfactory.” • The remark on Section 91.119, “Minimum Safe Altitudes” that “provides that no person may operate an aircraft at an altitude of 500 [ft.] AGL except over open water or sparsely populated areas.” Additionally, “aircraft may not be oper- ated closer than 500 ft. to any person, vessel, vehicle, or structure,” which certainly applies to offshore wind energy projects. • A final statement that “Under Part 77 the FAA does not consider impacts to emergency operations in an aeronau- tical study because they would not occur on an ongoing or regular basis and, therefore do not reach the level that could be considered significant.” Upon initial analysis, this statement conflicts with an earlier Recommended Practice Example and considerations used in the United Kingdom to evaluate overall acceptability. 3.2.6 Case Study: Fire Island Wind Farm and Anchorage International Fire Island, located west of Ted Stevens Anchorage Inter- national Airport (ANC), is the location of Alaska’s first com- mercial wind farm that went into service in the fall of 2012. Figure 3.21 shows the geographic proximity of the wind farm and the airport. Fire Island provides an interesting case study of the impacts of wind turbines on airspace and the process of evaluation and mitigation. A private development company proposed a wind project on Fire Island in the early 2000s and an application to the FAA included 36 WTGs. The FAA conducted an aeronautical study under provision of U.S. Code, Title 49, section 44718 and Code of Federal Regulations, Title 14, part 77.95 The evaluation Figure 3.21. Fire Island wind farm and Ted Stevens Anchorage International Airport. 95FAA, Aeronautical Study No. 2004-AAL-104-OE, 2008.

40 study scrutinizes the impact of wind turbines on (a) airport facilities; (b) operations; (c) procedures; (d) physical, electro- magnetic, and visual interference on navigation and naviga- tional aids; and (e) airport capacity. The impacts identified by the FAA included the following: • Of the original 33 turbines, 22 exceeded 600 ft. above mean sea level (MSL), as per Part 77, Section 77-3 (a). These 22 turbines would have affected the CAT III Instrument Landing System (ILS) instrument approach procedure into ANC. • VHF Omnidirectional Radar (VOR) and ASR-8 radar at ANC would have experienced adverse effects due to electro- magnetic interference (EMI), wind turbine height, and wind blade turbulence. • Wind turbulence would have led to unsafe departure for small aircrafts if they were to adhere to the departure pro- cedures. (Note: Wind turbulence was not part of the scope of the aeronautical study). • No impacts would have been incurred upon long-range surveillance radars. In 2008, the FAA approved a 24-turbine project, objecting to the other 12 turbines due to airspace impacts. Even the 24-turbine approval required a number of mitigation mea- sures to preserve the airspace capabilities at ANC, including the following: • The FAA required that the height of five of the 24 WTGs must be decreased because no wind turbine can have height above 600 ft. MSL and mast height above 250 ft. MSL. • A new VOR was constructed on the mainland near the air- port and the old VOR was decommissioned. To address VOR EMI, Doppler VOR replaced conventional VOR. This specific change in technology allows for broader changes in approach/ departure procedures to improve air traffic management. • Wind turbulence effects warranted replacement of ASR-8 with ASR-11. • VFR aircraft departing/arriving Anchorage area avoiding Anchorage Class C airspace were restricted from flying over Fire Island on northbound routes. Fire Island was reclassified as “congested” airspace, requiring planes to stay 1,000 ft. above the tallest structures on the island. • All structures were required to be marked and/or lighted in accordance with FAA AC 70/7460-1K,96 including white paint and synchronized red lights. Since 2008, 11 of the wind turbines have been constructed and currently generate enough electricity to power an average of 5,600 homes. 3.2.7 Lessons Learned While some energy technologies have not been closely evaluated for potential impacts on aviation, this is not the case for wind energy. Due to its capacity to produce a signifi- cant amount of renewable energy and achieve public policy mandates for renewable energy, high demand to construct wind projects has forced aviation and military stakeholders to respond to encroachment on the NAS, garnering wind energy installations close scrutiny since at least 2006. The lesson of wind energy and aviation has been the need to compromise. Wind energy provides important benefits for national security, economics, and the environment. However, airspace is a finite resource, central to supporting commercial and recreational aviation, emergency response, and military readiness. Project development is subject to a review process facilitated by the FAA and contributed to by the military and other government agencies with a variety of interests. Through that process, individual projects must demonstrate how they are avoiding and minimizing impacts on airspace and, if required, how they will mitigate for unavoidable impacts. The approval may be an opportunity to restrict air- space around the wind farm and enhance airspace in areas where the supporting system needs improvement. After about 10 years of active dialogue on the matter, research and compromise will continue to be necessary. The DOE, FAA, DHS, and DoD have taken lead roles in this process, as evidenced by the IFT&E Program and its focus on devel- oping radar mitigation technologies that can be deployed throughout the country. Interagency coordination, building on successful projects like the DoD Siting Clearinghouse, will be important for avoiding and mitigating potential problems early in the process. 3.3 Oil and Gas Drilling 3.3.1 Research Context Advances in technology used to extract oil and natural gas from subsurface reservoirs have recently produced a boom in production. Previously, reserves trapped in shale formations, which are typically narrow bands of tightly packed sedimentary rock, were not economically productive. Over the past decade, two important breakthroughs have facilitated the cost-effective removal of these shale reserves. The first advancement is the optimization of horizontal directional drilling, a technique cre- ated as an effective way to install underground conduits such as water lines and electrical cables, to extend the drill bit into 96FAA, Advisory Circular 70/7460-1K, Chg. 2, “Obstruction Marking and Light- ing,” Chapters 4, 12, and 13: http://www.faa.gov/regulations_policies/advisory_ circulars/index.cfm/go/document.information/documentID/74452.

41 the narrow reservoirs and parallel to the above-ground surface. The second advancement is expansion in hydraulic fracturing, a process where water, chemicals, and sand are injected into the shale to break it apart and release the oil and gas product. These new techniques are sometimes referred to as unconventional production, whereas conventional production is distinguished by well drilling into a reserve where oil and gas readily flow to the wellbore. Much of the reserves that are released are in the form of gas (i.e., dry reserves) though some less mature prod- uct includes some oil as well (i.e., wet reserves). According to the U.S. Energy Information Agency (EIA), dry shale gas expanded four-fold between 2006 and 2010, constituting 23% of total gas production. Wet gas reserves composed an additional 21% of total domestic reserves. Of all the natural gas consumed in the United States in 2011, 95% was from domestic sources. Figure 3.22 shows shale gas reserves in the United States. Areas defined as “plays” are being actively explored. Due to the potential access to cleared flat land within some of the shale plays, many airports have been approached by energy companies about leasing land for exploration and extraction. Recent legislation under the “FAA Modernization and Reauthorization Act” of 2012 has provided communities that operate GA airports with enhanced flexibility to utilize oil and gas revenue for non-airport improvements. Figure 3.22. U.S. shale gas resources. CRITICAL RESEARCH NEED—Oil and Gas Drilling Evaluate airport management of proposed oil and gas projects to date and use their lessons learned to inform guidance for future airport drilling projects.

42 3.3.2 What Are the Impacts of Oil and Gas Drilling? Whether conventional or unconventional, drilling requires a number of similar facilities. The hydraulic fracturing (i.e., fracking) necessary to develop oil and gas from shale deposits requires additional support components. Figure 3.23 depicts some of the most common facilities. First, a well pad is constructed, which provides a stable platform for facilities and activities during both construction and operations. The well pad is about 5 acres in area and can be reduced to about 3.5 acres to support long-term use. Two types of drill rigs are most commonly used in current drilling programs. The larger is a Nomac Rig, which has a height of 173 ft. AGL. A smaller but less efficient rig is referred to as a mountain rig, which is 103 ft. tall. The rigs need to be able to drill into the ground to reach shale reserves, which are about 8,000 ft. deep. In comparison, shallow wells that are used to extract traditional reserves are closer to a few thou- sand feet below ground. The drill rigs are a temporary pres- ence, as shale wells can be drilled over about a 30-day period. A “workover” rig, which is between 80 and 90 ft. tall, is then brought in to clean up and stabilize the well. One of the unique components of the hydraulic fractur- ing process is the need for an abundance of purified water, which must be available over a very short period when the fracturing is conducted. This necessitates the construction of fracking ponds near well sites that can be pumped under pressure into the well over a 4 to 7 day period after the well has been drilled and worked over. The ponds at existing well sites near airports are about 3 acres in size. The frack ponds are only needed during the fracking process but are costly to Figure 3.23. Typical facilities required for hydraulic fracturing.

43 develop and reclaim, and therefore are often reserved in place for future fracking operations. The infrastructure that is left in place on the well pad after construction is relatively low profile and non-intrusive. The actual wellhead consists of some pressure valves that are about 8 ft. above the ground. Separation tanks used to remove other fluids from the product are about 5 ft. tall. Storage tanks that provide temporary storage of separated product can be 12 ft. tall. The tallest structure on a typical fracking installation is a communication tower, which can be as high as 50 ft. AGL to facilitate remote monitoring of production activities. Other components of a wider drilling network include a compressor station that pressurizes the gas for delivery through a regional gas pipeline delivery network, a water pipeline network for delivery of water to the frack ponds, and deep injection wells that are used for discharging process water after it is used and collected post-fracturing. Once the drilling pad is constructed along with all other supporting infrastructure, the drill rig is erected. Drilling takes about 30 days. Then a workover rig is brought in to clean and stabilize the well, often including the flaring of excess gas, last- ing up to one week. Then the well is fracked over the next 4 to 7 days and, finally, the well is put into production. 3.3.2.1 Physical Penetration of Airspace The airspace issues that arise from oil and gas development include physical penetration of the Part 77 imaginary surface during the drilling period and for permanent operational infrastructure, non-physical penetration associated with flar- ing of waste gas during the wells’ development, and wildlife hazards associated with frack ponds. Figure 3.24 depicts the relative size of various oil and gas development infrastructure against a generic airspace surface. Physical penetration of airspace is most significant in associa- tion with the drill rigs. Temporary penetration of airspace is commonly approved by the FAA through the filing of a Form 7460, typically when a crane is needed for construction. How- ever, such approvals are only provided when there is no other practical alternative. When conventional drilling is proposed, the energy company may be able to justify the need to locate a well rig closer to the airport so that the wellbore reaches an area where the oil or gas resources are more accessible. The capability of horizontal directional drilling with its ability to access reserves horizontally diminishes the need to locate above-ground infrastructure closer to a reserve, although cost may be considered as part of an alternative analysis. When the drilling company determines that it will benefit from locating the drill rig closer to airport infrastructure, it may choose to deploy the shorter mountain rig. At 70 ft. shorter than the Nomac rig, the mountain rig can potentially be sited as much as 500 ft. closer to the airport, assuming the 7:1 set-back ratio that establishes the approach surface (see “Obstruction Height Zones” under Section 2.5). The permanent facilities associated with oil and gas drill- ing are considerably shorter and unlikely to produce airspace issues. At about 50 ft. tall, the communications tower may represent a physical penetration or even obstruct radar sig- nals, both of which would necessitate an airspace review by the FAA. The other structures occupying the drilling pad are typically 12 ft. tall or less and are thus inconsequential to airspace. 3.3.2.2 Flaring A non-physical penetration issue associated with oil and gas drilling is the process of gas flaring (Figure 3.25 is an example). Flaring is conducted during the development of oil and gas wells for several reasons. In some cases, gas is flared off because it is considered waste product when the primary reserve may be oil. In other cases, the gas is being released during well testing and stabilization and, therefore, must be flared as part of the process of establishing and confirming Figure 3.24. Fracking structures.

44 the well’s development. Regardless of the reason, customary practice for flaring is to erect a temporary stack and direct the gas through the stack for combustion. Beyond the physi- cal height of the structure, there are potential non-structural impacts from the flame and the heat levels above the flame. The height of impact is not well understood for several rea- sons, including the fact that the height of the flame will vary based on the characteristics of the gas being combusted and the height of thermal impacts above a visible flame is difficult to characterize. 3.3.3 How Are Impacts Characterized and Managed? In the oil and gas area, much of the understanding of potential impacts on airports and airspace has been gained as the result of reviewing individual project proposals. This experience has helped inform FAA guidance, as described below. 3.3.3.1 Projects at Airports Airports offer favorable site conditions for the exploration and development of oil and gas facilities. The cleared and open management of land facilitates easy access over the land for exploration and development. There is ready access to infra- structure that support testing and development. Airports also provide energy companies ease of partnership in executing a single lease for one large property, rather than assembling a patchwork of landowners. Additionally, airports are favorable to consideration of business offers to lease land for oil and gas development as an alternative revenue source. Table 3.2 provides an unofficial list of airports where oil and gas drilling activities have occurred. When Denver International Airport (DEN) opened in 1995, its land area included 49 pre-existing mineral oil and gas wells. (Another 25 wells were closed and capped due to the airport’s construction.) By 2010, 27 additional well leases had been approved and developed, totaling 76 active wells. All current wells are vertical, although there has been interest in Figure 3.25. Gas well flaring. Airport Code State Airport Code State DENVER INTL DEN CO STROTHER FIELD WLD KS GREELEY-WELD COUNTY GXY CO JEFFERSON COUNTY AIRPARK 2G2 OH FRONT RANGE FTG CO WHEELING OHIO CO HLG OH DURANGO-LA PLATA COUNTY DRO CO INDIANA COUNTY/JIMMY STEWART FLD IDI PA ANTHONY MUNI ANY KS BRADFORD RGNL BFD PA SHALZ FIELD CBK KS JOHN MURTHA JOHNSTOWN-CAMBRIA CO JST PA GARDEN CITY RGNL GCK KS DUBOIS RGNL DUJ PA GARDNER MUNI GDM KS JOSEPH A. HARDY CONNELLSVILLE VVS PA GREAT BEND MUNI GBD KS ROSTRAVER FWQ PA HUGOTON MUNI HQG KS PITTSBURGH INTL PIT PA LIBERAL MID-AMERICA RGNL LBL KS ALLEGHENY COUNTY AGC PA MEDICINE LODGE K51 KS NEW CASTLE MUNI UCP PA NEW CENTURY AIRCENTER IXD KS DALLAS/FORT WORTH INTL DFW TX PRATT RGNL PTT KS JACK BROOKS RGNL BPT TX TRIBUNE MUNI 5K2 KS DENTON MUNI DTO TX WELLINGTON MUNI EGT KS ODESSA-SCHLEMEYER FIELD ODO TX Sources: Direct inquiries by HMMH, Inc. and responses to a survey distributed by the FAA Table 3.2. Unofficial list of airports with oil and gas drilling activities.

45 exploring horizontal wells to tap oil and gas potential under airport facilities. The airport’s lease approvals addressed exist- ing and future facilities including runway expansion to the north. All drilling sites are located outside of the Building Restriction Line. Permanent structures are relatively short (e.g., 15–20 ft. AGL). To perform maintenance on the wells, approximately every 18 months, companies must bring in large cranes (about 100 ft. tall), which are in place for up to 2 weeks. The companies must file a Form 7460 each time a crane is brought in for maintenance. Jimmy Stewart Airport (IDI), a GA airport located in Western Pennsylvania, was approached by an energy com- pany about drilling in 2006. Seven shallow wells (at a depth of 3,000 ft.) were drilled in 2008; one deep “Marcellus” well (8,000 ft.) was drilled in 2009. The rig was 142 ft. tall and was located 750 ft. from the edge of the runway. Two additional deep wells are proposed. The shallow wells were drilled in 7 days; the Marcellus well took 30 days. The FAA determina- tion stated that the proposed facility would not affect IFR operations or penetrate Part 77 surfaces. A frack pond was constructed, and the water was used to frack the well and release the trapped gas. Once completed, the frack pond was reclaimed in accordance with FAA specifications. Figure 3.26 provides a photo of the drilling operations. Figure 3.27 shows the location of airports in Western New York, Pennsylvania, and Eastern Ohio that overly the Marcellus Shale Play. While development of new gas wells has slowed over the past year due to a large supply and decreas- ing prices, discussions with several airports in this region suggest that they are fully aware of the natural gas drilling potential and see future business arrangements with energy companies as presenting an opportunity to develop alterna- tive revenue sources. 3.3.3.2 FAA Oil and Gas Drilling Guidance Oil and gas development, like other non-aeronautical activ- ities, is subordinate to the public airport use of airport land at “federally obligated” airports. The FAA is in the process of finalizing an AC titled “Guidance on the Extraction of Oil and Gas on Federally Obligated Airport Property” to ensure that such activities are carried out appropriately. The specific pur- pose of the AC is (1) to assist airport sponsors by identifying applicable laws and regulations and FAA orders and guidance documents applicable to the FAA’s review of proposed oil and gas activities and (2) to assist FAA Airports’ field offices with the timely review of ALP changes, on-airport construc- tion and airspace notification, Construction Safety Phasing Plan, environmental reviews, and applicable grant assurances for acceptable oil and gas development and operations on federally obligated airport property. The AC is informed by the FAA’s oversight of proposed oil and gas development proj- ects, including those implemented on airports such as DEN, IDI, and DFW. In planning and approving oil and gas development, airport sponsors must ensure that: • Oil and gas development does not conflict with current or planned aviation uses. • Associated infrastructure meets airport design standards to ensure safe and continuous airport operations. • Proposed infrastructure is identified on the ALP. • Development conforms to applicable environmental stan- dards and industry best management practices. • Resulting revenue is collected and spent in accordance with the FAA’s Revenue Use Policy and in compliance with grant assurances 24 and 25. These requirements apply for both projects that are located on the surface of airport property, as well as those that pen- etrate into subsurface grounds below airport property. This has been referred to as a “behind the fence” project. However, projects with a surface presence on airport land have a signifi- cantly more complex involvement from the FAA. The primary steps in the process are provided in Fig- ure 3.28. In each step, the airport sponsor must ensure that the development project meets FAA requirements. It starts with notifying the FAA Regional Office and ADO about the proposed activity, ensuring that the terms of the lease meet both the subordination of the activity to aviation uses and procurement and financial equity obligations, and provid- ing regular submissions to the FAA for each step in devel- opment to ensure that the project meets airport planning, safety, and environmental requirements. The AC spells out the process for both regional staff and airport sponsors. Some of the critical obligations associated with compatibility are provided below. Figure 3.26. Drill pad and frack pond at Jimmy Stewart Airport, PA.

46 Figure 3.27. Airports located in the Marcellus Shale Play. Figure 3.28. Approval process for oil and gas drilling.

47 Hazard Mitigation: One of the common assurances that projects must meet is Hazard Mitigation.97 Under this assur- ance, the design, construction, and operation of the project and related improvements (including fracking water ponds and wastewater management, drainage improvements, ditches, wetland mitigation, materials handling, landscaping, etc.) shall not create a hazardous wildlife attractant to the airport. FAA AC 150/5200-33 advises a 5,000 to 10,000 ft. separation distance between the airports Air Operations Area and a hazardous wildlife attractant. Additionally, the AC recom- mends that a 5-mile separation distance be considered when the attractant could cause wildlife movement into or across the approach or departure airspace. Existing frack ponds at DFW are subject to hazard wildlife mitigation requirements (see Section 3.3.4 below). For the single Marcellus well that was constructed at IDI, the energy company was required to reclaim the airport property after drilling to remove the frack pond due to its proximity to air operations areas. Airport Layout Plans: Another common assurance that must be met is maintaining a current ALP.98 The assurance requires the sponsor to update the ALP for any proposed changes where aeronautical uses are transferred to non-aeronautical uses, or where above-grade structures are constructed (including sur- face roads). Such updates must be submitted to the FAA for approval. The following oil and gas extraction facilities should be included on the ALP: • Well pad sites. • Well heads, including injection wells. • Fracturing fluids storage pits and ponds. • Dehydrator and compressor stations. • Access roads. • Other buildings or facilities. • Other leased areas. Oil and gas infrastructure associated with distribution of product to off-airport facilities must also be identified on the ALP and may include: • Transmission lines. • The collection and distribution of extracted fluids. • Collector oil and gas pipelines. • Fracturing fluid pipelines. • Utilities serving the well site. Because the exact location of these facilities will not be identified during planning stages when the FAA is review- ing the project, the ALP should specify facilities and areas. Once facilities are constructed, the ALP can be changed to show the as-built locations. The approval of the ALP update means that the sponsor can proceed with obtaining other regulatory approvals, such as an airspace safety determination or approval under the National Environmental Policy Act (NEPA). The approval of the ALP is considered a federal action, which automatically triggers NEPA review to ensure that the proposed work is consistent with NEPA. Safety Management Systems (SMS) and Safety Risk Man- agement (SRM): Safety Management Systems (SMS) are an integrated collection of practices, procedures, and programs ensuring a formal approach to safety through risk man- agement.99 Safety Risk Management (SRM) is a formalized approach to safety. All oil and gas development projects must be implemented in accordance with the airport sponsor’s SMS. The sponsor should notify the FAA Regional Office or ADO early in the process to determine the need or require- ments for SRM. All construction proposed for well drilling, site development, and associated infrastructure must be submitted to the FAA in the form of a Construction Safety Phasing Plan (CSPP). The required content for the CSPP is available in AC 150/5370-2F, “Operational Safety on Air- ports During Construction,” which includes the following elements: • Emergency/Fire/Medical Response. • Blowout Response. • Storm water runoff management. • Spill release response and containment of hazardous materials. • Disposal and containment of hazardous materials. • Compliance with federal, state, and local airport rules and regulations. • Wildlife and uncovered ponds and waterways management. • Airport areas and operations affected by the construction activity. • Personnel and vehicle access. • Foreign Objects Debris (FOD) management. • Haul routes, roads, and excavation material storage and management. • Notification of construction activities (Form 7460). • Site monitoring, inspection, and enforcement respon- sibilities. Form 7460, “Notice of Proposed Construction or Altera- tion”: A sponsor proposing any type of construction or altera- tion of a structure that may affect the NAS is required to notify the FAA by completing the Notice of Proposed Construction or Alteration form (Form 7460). As part of the review, the FAA also evaluates the CSPP. A notice may be required for multiple phases of the project including exploration, devel- 9749 U.S.C. Section 47107(a)(9), “Hazard Mitigation (#20).” 9849 U.S.C. Section 47017(a)(16), “Airport Layout Plan (#29).” 99FAA, Order 5200.11, “Safety Management System (SMS).”

48 opment, and approval of the oil and gas production plan, construction at individual well sites, and well closure and reclamation. 3.3.4 Case Study: Dallas/Fort Worth International Airport (DFW) Dallas/Fort Worth International Airport (DFW) is located in the Barnet Shale Play. It was approached by energy compa- nies in the mid-2000s about opportunities to lease land for oil and gas development. With over 17,000 acres of land, DFW was a strong potential partner for oil and gas development. However, because such an extensive oil and gas development program had never been approved by the FAA, the airport and the FAA needed to work together along with Chesapeake Energy, the selected energy partner, to identify a leasing pro- cess and development network that could provide business success while protecting airspace and the environment. DFW also had its own approval process for which the drilling pro- gram would need to comply. This experience provides a useful model for future projects. Figure 3.29 shows the network of oil and gas facilities that have been developed at DFW. The shale resource is located between 6,500 and 8,300 ft. below the land surface. Table 3.3 lists the elements of DFW’s oil and gas development program by number of facilities. Figure 3.29. Oil and gas infrastructure at DFW Airport. Facility Number Exploration Pad Sites 35 Frack Ponds 8 Active Wells 114 Planned Wells 300 Miles of Pipeline 35 Table 3.3. DFW’s gas exploration infrastructure.

49 The planning of the project started with the ALP. Airport zones were set up to organize the planning process. No explo- ration or development was allowed in the Air Operations Area (AOA), the most secure part of the airport. No pipelines were allowed to be located under runways or other critical avia- tion facilities. Seismic investigations by the energy company focused in on the areas of highest interest. Facility require- ments were identified and based on planning guidance from DFW. Chesapeake Energy prepared a gas development plan. The closest pad to a runway is about 1,000 ft. Horizontal drill- ing allowed for extraction in areas closer to airport facilities, including the AOA. The distance of horizontal drilling is up to 1 mile. Figure 3.30 depicts a flight departing DFW over a gas pad in production. Evaluation of potential airspace impacts was conducted based on planning zones. This included evaluation of physical penetration of the Part 77 imaginary surface as well as poten- tial impacts on radars and ILS. DFW has two Air Surveillance Radar (ASR-9) sites on airport property that needed to be considered. It permitted a maximum structure height for each approved work zone. In evaluating the potential effect of the drill rig to the ASR-9, it was important to consider the angle of the rig to the radar. Chesapeake utilized the larger Nomac rigs where height was not an issue and the shorter Mountain rigs for areas closer to airport facilities. Rigs were required to be illuminated with yellow lights. Forms 7460 were filed for the planning zones with a maxi- mum structure height (e.g., 177 ft.). FAA determinations stated no objection with conditions. The following is a list of condi- tions that were included in many of the determinations: • A Form 7460 was filed for each individual structure proposed in the zone. • Due to an identified effect on Instrument Flight Rules (IFR) for existing or any proposed instrument approach procedures, the sponsor must coordinate at least 72 hours in advance of the start of construction in the work zone with required mitigation (these are specific to one of the determinations): – RNAV GPS RWY 17R: Raise the LNAV/VNAV DA from 1000 to 1144; raise the LNAV MDA from 1000 to 1100. There would be no effect if the construction height were limited to 700 ft. above mean sea level (AMSL). – RNAV GPS RWY 17C: Raise the LNAV/VNAV DA from 1065 to 1144; raise the LNAV MDA from 1000 to 1100. There would be no effect if the construction height were limited to 700 ft. AMSL. – ILS or LOC RWY 17C: Raise the S-LOC 17C MDA from 1000 to 1060. There would be no effect if the construc- tion height were limited to 700 ft. above AMSL. – RNAV GPS RWY 17R: Raise the LNAV/VNAV DA from 1000 to 1101; raise the LNAV MDA from 1000 to 1060. There would be no effect if the construction height were limited to 700 ft. AMSL. – RNAV GPS RWY 17C: Raise the LNAV/VNAV DA from 1065 to 1102; raise the LNAV MDA from 1000 to 1100. There would be no effect if the construction height were limited to 700 ft. AMSL. • The Airport Sponsor is responsible for all local NOTAMs for work in and around the project area. • The construction equipment associated with the project will be located very close to an FAA ASDE-X radar system, which is located approximately 2,400 ft., north-northeast from the proposed project site. The FAA National Field Support Office, ATO-W NASE, has conducted preliminary on-site modeling and simulation of a drill rig at the pro- posed site, using fire trucks with elevated ladder aerials. The results did not yield any adverse effects; however, the equipment used was approximately 1/20 the signature that an actual drill rig will present to the ASDE Radar System. Prior to erecting a drill rig at this site, the Sponsor shall coordinate with the FAA’s D-10 Systems Operations Center (SOC) for coordination with the FAA Technical Operations Radar SSC organization, to have them actively monitor and assess the West ASDE systems’ operation during the erection, including checking the initial full extended height configuration, and preparing the fully loaded drill rig pipe rack. This initial monitor and assessment period is expected Figure 3.30. Aircraft departing DFW over gas pad in production.

50 not to exceed more than 3 days. The sponsor may not start drilling operations until the initial ASDE operational monitoring and assessments have determined that no adverse operational effects have been observed from the drill rig. • Given that construction equipment is proximate to Runways 17L, 17C, 18L, and 18R, construction equipment should be lowered close to the ground when not in use. • The drill rig should be lighted with yellow fluorescent lights within the vertical channels of the drill rig and have a red light on top. • The sponsor should ensure that light from the construc- tion equipment should not interfere with air traffic or air operations. • The sponsor should coordinate construction activity with the ATCT. • All construction should be compliant with AC 150/5370-2E, Operational Safety on Airports during Construction. • The project has a 1-watt communications monitor and control system and associated 43 ft. tall antenna for the gas well equipment that will remain. Prior to transmit- ting from this site, the sponsor shall coordinate with the FAA’s D-10 SOC to ensure that there no adverse impacts on FAA systems. The FAA dedicated staff resources to the airspace safety review to ensure that it was conducted in a comprehensive and efficient manner. DFW and FAA developed procedures to facilitate the reviews. Form 7460 packages were comprehensive when submitted. FAA completed its review in a 90-day period. About 99% of the notices were approved.100 The most important standard was to have no long-term impact on the ILS. Impacts to ILS were limited to a 24 to 48 hour period. Some limited impacts on RNAV/RNP were considered acceptable. Short-term mitigation was employed by increasing the decision height. DFW’s approval process prohibits the flaring of the well as part of clean up. The Construction and Fire Prevention Stan- dards Resolution and Amendments to the Codes updated in February 2011 under Part 9, Section 14 (n) states “Gas Emis- sion or Burning Restricted. No person shall allow, cause or permit Gas to be vented into the atmosphere or to be burned by open flame except as provided by law or permitted by the Commission.” Eight frack ponds remain in place to support future drill- ing. Each is about 3 acres in area. Figure 3.31 shows an image of one of the ponds. The most significant concern from an air- space safety perspective is the ponds’ potential impact as wild- life attractants. Thus, the ponds were designed to discourage wildlife by utilizing a block configuration, slippery liners, and steep slopes. The pond could not include capability for drain- ing, as the soils down-gradient are highly erodible. To dis- courage waterfowl from using the ponds, a network of wires spaced about 10 ft. apart was spread across the top of the ponds. Reports indicate that this system has been effective in keeping waterfowl out of the ponds. These ponds were approved in 2007. Future ponds may be required to be cov- ered to better ensure against a wildlife hazard. 3.3.5 Lessons Learned The development of oil and gas programs at several exist- ing airports provides useful information for considering best practices and guidance. The flaring of wells has been a dif- ficult impact to measure because the influence of flames and associated heat is variable and not well defined. Moreover, energy companies have alternative methods to achieve the same result. Referencing the case study example, DFW does not allow flaring, so the drilling company is required to either shut the well until regulator valves are installed or, if appli- cable, run the gas through pipeline connections from the lat- eral pipelines in to the main pipeline system. Frack ponds are also a concern from a wildlife attractant perspective. At some airports, frack ponds have been con- structed as temporary facilities to support the drilling opera- tions and then returned to their pre-existing condition. In other cases, frack ponds have been retained as a facility to support future well development. Permanent facilities have been designed to include wildlife-discouraging attributes that may be useful for future projects, such as those at DFW. The development and implementation of the DFW Oil and Gas Program also offers lessons in the level of coordination 100Barrett, S., Personal communication with Steven Tobey, DFW Manager of Airfield Operations, Harris Miller Miller & Hanson, Inc., February 4, 2013. Figure 3.31. Frack pond at DFW with cross wires and flags to discourage waterfowl.

51 with the FAA necessary to efficiently review and determine potential impacts on airspace of a variety of temporary and permanent structures associated with drilling and how to successfully manage the impacts. 3.4 Power Plant Stacks and Cooling Towers 3.4.1 Research Context Amid all of the new energy technologies being developed, traditional combined-cycle steam power electricity gen- eration, fueled by an abundance of natural gas, continues to play an important role in the country’s baseline energy net- work. According to the Federal Energy Regulatory Commis- sion (FERC), 33% of all new electricity generation capacity constructed in 2012 was from natural gas-fired power plants (compared with 40% from wind and 17% from coal). Com- bined-cycle steam electricity generating plants are important because they produce electricity on demand (while wind pro- duces when the wind blows and solar when the sun shines). In this respect, a more recent use of these facilities has been construction of smaller peaker plants, which are activated only when electricity demand spikes in summer and winter. Other fuel sources of power plants include oil, coal, biomass, and CSP. Those that burn fossil fuels are equipped with stacks that release a heated exhaust. Some steam electricity genera- tion plants also have cooling towers that release waste heat from fuel combustion into the atmosphere (see Figure 3.32). These facilities are large and often are reviewed for airspace impacts due to physical penetration. However, it is the non- physical penetration impacts associated with thermal and vapor plumes that have been of particular interest of aviation stakeholders. Thermal and vapor plumes can create a potential hazard to aircraft flying above the stack in the form of turbulent Figure 3.32. Cooling towers and vapor plume. gusts which can cause potential upset of the aircraft. This sec- tion describes the potential impacts from power plant stacks and cooling towers on airports and aviation. 3.4.2 Characterizing Impacts 3.4.2.1 Overview Whether from the stack or the cooling tower, the potential impacts occur when heated air rises from the power plant destabilizing the air environment and potentially disrupt- ing aircraft. Smaller fixed-wing aircraft are particularly at risk due to their relative lightweight airframe, as turbulence could affect the control and maneuverability of aircraft. The exhaust gas is emitted from stacks as a result of the fuel com- bustion from natural gas, diesel oil, coal, or biomass used to power electrical turbines or steam generators. Gas turbine exhaust can reach up to 1,100°F for larger stations.101 Cooling towers produce thermal plumes when heated “cool- ing” water is exposed to ambient air and the waste heat is trans- ferred to the ambient air and rises. Cooling tower plumes can also present visual impacts when the plume is saturated by moisture and the exhaust steam condenses with cooler ambient air similar to seeing one’s breath on a cold winter day. The abil- ity to see a plume depends on the type of release and weather conditions. The visible plumes could obscure the line-of-sight for pilots and ATC. In comparison to invisible vapor plume, the visibility of thermal plumes can be considered a benefit because potential turbulence can be seen and avoided (see Figure 3.33). Furthermore, plume abatement technologies using air to air heat exchangers to allow the mix of ambient air into the plume before it leaves the stack are available for cooling towers to limit the size and frequency of the visible plumes. The exhaust temperatures and exit velocities for cooling tower plumes tend to be lower compared to the peaker and combined-cycle stacks. Even though cooling towers tend to have a less buoyant plume (due to lower temperatures and exit velocities), the stack diameters tend to be larger, which 101Environmental Protection Agency (EPA), “Technology Characterization: Gas Turbines,” December 2008. CRITICAL RESEARCH NEED—Power Plant Stack and Cooling Towers Conduct a comprehensive review of the issues related to structure height and aviation safety impacts from thermal and vapor plumes to inform a consolidated set of guidance.

52 correlates to a larger mass flow and larger plume lateral dimen- sions. The larger lateral plume dimensions result in larger potential impact areas to aircraft when flying over a facility and their effects last longer when compared to the smaller diameter stacks with higher velocities where the potential duration is relatively small due to the smaller stack area. Table 3.4 presents a comparison of exhaust parameters for a typical peaker plant, combined-cycle facility and a cooling tower. The peaker plant has the lowest stack diameter but the highest exit velocity and temperature compared to the combined-cycle and cooling tower sources. The cooling tower has the highest stack diameter but the lowest exit velocity and plume temperature. 3.4.2.2 Turbulence and Aircraft Upset Exhaust plumes generated by the combustion of gases and discharge of waste heat have the potential to create in-flight hazards that affect the control and maneuverability of the aircraft. Under certain conditions, the plumes generated by the facilities can create turbulent conditions for aircraft that fly over or through plumes. In reviewing FAA guidance in the AIM,102 the FAA has devel- oped turbulence intensity reporting criteria characterized in the following four categories: 1. Light Turbulence: Momentarily causes slight, erratic changes in altitude and or attitude (pitch, roll, and yaw). 2. Moderate Turbulence: Similar to light turbulence, but of greater intensity; changes in altitude and/or attitude occur but the aircraft remains in positive control at all times. 3. Severe Turbulence: Causes large, abrupt changes in alti- tude and/or attitude; usually causes large variation in indi- cated airspeed; aircraft may be momentarily out of control. 4. Extreme Turbulence: Aircraft is violently tossed about and is practically impossible to control; may cause struc- tural damage. NOAA has also developed vertical acceleration ranges in terms of G-force, or Gs on aircraft for each turbulence inten- sity category. G-force is technically not a force, but a measure- ment of acceleration felt as weight per unit mass. For flight, the G-force is typically experienced by the pilot on the body during sharp turns, acceleration, or combination of speed and direction. NOAA has defined the four categories of turbulence relative to the degree of sudden change in vertical acceleration of an aircraft, in terms of G-force: 1. Light Turbulence: 0.2 G to 0.5 G 2. Extreme Turbulence: Greater than 2 G 3. Moderate Turbulence: 0.5 G to 1 G 4. Severe Turbulence: 1 G to 2 G The proximity of the plume and aircraft will also affect the potential impact. As illustrated in Figure 3.34, a plume con- tacting one side of the plane under the wing represents the maximum roll angle excursion, whereas a plume contact- ing the underbelly of the plane produces the maximum load factor change. The first example will cause an abrupt lateral imbalance in flight. The second will cause the entire plane to experience a dramatic change in lift. Where the plume is invis- ible, the pilot may experience larger pitch or bank excursions because of the unexpected nature of the plume’s effects. 3.4.2.3 Flight Tests Several flight tests have been conducted to assess aircraft handling characteristics and responses when penetrating a convective thermal plume emanating from a power plant. One test was conducted in November 2010 at the Calpine Sutter Power Plant in Sutter County, California.103 Nine passes were conducted between 500 and 1,000 ft. above the power plant stack. The pilot concluded that no turbulence was detectable at 1,000 ft. At 750 ft., the turbulence was character- ized as a “slight burble.” At 500 ft., a very slight aircraft upset was experienced requiring only minor flight control inputs to maintain level flight. The observer determined that the upset for pitch and roll axis never exceeded 7 degrees. A slight altitude increase and rate of climb were also experienced. The observers concluded that the power plant plume did not rep- resent a significant threat to GA aircraft operating at traffic pattern altitudes. Figure 3.33. Visible vs. invisible plumes. 102FAA, Aeronautical Information Manual (AIM), “Turbulence Reporting Criteria,” Table 7-1-10: http://www.faa.gov/air_traffic/publications/ATpubs/AIM/aim0701. html#aim0701.html.49. 103Wardell, D. and D. Moss, “Joint Flight Test: Aircraft Handling Characteristics During Convection Plume Penetration,” Calpine Sutter Power Plant, California, 2010.

53 A second test was conducted at the Indigo Energy Facil- ity near Palm Springs, California.104 This test included two planes, one equipped with a Data Acquisition System and the second with the ability to collect photographic docu- mentation. Data were collected for cruising configurations that would be expected in this area. The height of flights was dictated by the height of existing nearby structures, which were utility-scale wind turbines. All flight traffic must stay a minimum of 500 ft. above the wind turbines. When the air- craft entered the plume, the typical response was an abrupt but minor change in pitch, angle of attack, and occasionally bank angle when the plume interacted with just one wing. In all cases, the aircraft stabilized on its own within 1 second of exiting the plume. Consequently, the pilots had no difficulty maintaining control of their aircraft. In a third study, two flight tests were flown through the thermal plume of the Walter E. Higgins Power Plant near Primm, Nevada.105 The data collection was similar to that collected at the Indigo Energy Facility, but included both cruise and landing configurations. A variety of heights above the stack were flown, although data collection was focused on 500 ft. above the facility’s Air-Cooled Condenser (ACC). The aircraft response to the plumes varied from high-frequency/ low-amplitude aerodynamic chop to oscillatory bank angle changes of up to 25 degrees of bank. The variations generally were more prominent when the aircraft was closer in altitude to the source of plume. Since the ACC was adjacent to the Heat Recovery Steam Generators (HRSG), some of the aircraft responses were likely due to the HRSG plume as opposed to the ACC plume. For those points where the ACC was the con- tributor, the aircraft response was more benign. Even at 500 ft. above the facility, the aircraft was fully controllable and recovery from any dynamic upset was fully within the capability of a student pilot with limited experience. Facility Type Stack Diameter (ft.) Exit Velocity (fps) Temperature °F Eastshore Energy Center Peaker Plant 3.96 76.9 713 Blythe Energy Project Phase II Combined Cycle 21.5 39 252 Blythe Energy Project Phase II Cooling Tower 30 31.4 57 Table 3.4. Comparison of different stack and exhaust properties. Figure 3.34. Variance of turbulence impact on aircraft dependent on position relative to plume. 104Moss, D., “Flight Test Report: Aircraft Handling Characteristics during Con- vection Plume Penetration of Indigo Energy Facility, California,” 2010. 105Moss, D., “Flight Test Report: Glint/Glitter Evaluation of SEGS and Convection Plume Evaluation of Walter Higgins Power Plant, California,” 2010.

54 3.4.2.4 Modeling Potential Impacts—MITRE Study There have been numerous studies conducted by consul- tants and government agencies to evaluate exhaust plumes and the potential hazard to aircraft. Recently, MITRE released its long awaited study for FAA on the effects of vertical plumes on aviation.106 The study included the development of a Plume Hazard Model to evaluate potential plume behavior from an exhaust stack along with the potential impact the plume could have on aircraft performance when flying over or near the exhaust stack. The MITRE study is a follow-up to the FAA’s “Safety Risk Analysis of Aircraft Overflight of Industrial Exhaust Plumes” (January 2006), which examined 671,000 pilot reports over 30 years, along with more than 150,000 accident and incident reports from the FAA National Aviation Safety Data Analysis Center (NASDAC) Accident/Incident Data System (AIDS). The purpose of the study was to evaluate the potential safety risk hazards associated with the following: • Plumes that could result in possible airframe damage and/ or possible effects on the aircraft stability. • The effects of high water vapor plumes, engine/aircraft contaminants, icing, and restricted visibilities produced by these plumes. The safety risk study findings indicated that the risk of an accident from an over flight of a small plane was low; how- ever, the report did note that there is the potential for aircraft upset to occur when flying in the immediate vicinity of the exhaust plume. As a follow up to the FAA’s “Safety Risk Analysis,” MITRE developed the Plume Hazard Model to predict the potential effects of thermal plumes on aircraft. The model has the abil- ity to evaluate plume rise and plume characteristics from an exhaust stack while also incorporating turbulence and aircraft response models to evaluate the degree of turbulence that could be expected above the exhaust stack and its effect on different aircraft types. The plume model allows a user to model the exhaust stack(s) to evaluate the area to avoid around the plume during certain weather conditions. The model can also estimate elevated temperatures and oxygen content of the plume above a stack, which can be used to assess potential hazards to helicopters. The MITRE report found that there was a definite risk of light aircraft experiencing severe turbulence within the target level of safety (TLS) as they fly over an exhaust plume during certain weather conditions. The report did find that it was unlikely that an aircraft would reach upset criteria, or a condition that causes the aircraft to pitch or bank at certain angles causing the aircraft to lose control. The MITRE study was conducted in response to pilot con- cerns of thermal plumes and their potential to create turbulent conditions for aircraft and the increasing aviation incidents involving plumes both in the United States and internation- ally. There are numerous examples, especially in California, of aircraft affected by power plant plumes during take-off and/or landing at airports.107 The Oregon Pilots Association is currently commenting actively on the potential thermal plumes and visual impacts from cooling towers with the siting of two proposed power plants near the North Bend and Trout- dale airports in Oregon.108 The MITRE study builds upon the FAA “Safety Risk Analysis” and guidance from the Australian Civil Aviation Safety Authority (CASA) (see Section 3.4.3.1) to develop a unique modeling tool to evaluate plume characteris- tics and dispersion once they leave the stack and to address the potential impact to aircraft. The Plume Hazard Model is composed of several com- ponent models. One model evaluates the plume velocity after it leaves the stack. Two other models incorporate aircraft response to predict the effect of the plume on three different types of aircraft. The model is run via a graphical user interface (GUI) where the user can input stack parameters, including single and merged stacks, meteorological conditions, gust percentile, and aircraft type. Three aircraft type are available within the model for evaluation ranging in size and weight— North American Navion, a Lockheed Jetstar business jet, and a Convair CV-880M jet. The model will produce the “Maximum Vertical Acceleration” plot, which shows areas above the exhaust stack where light, moderate, severe, and extreme turbulence could be experienced for different size aircraft based on the user inputs. This can help a pilot identify the area of potential severe turbulence and avoid such region around the exhaust stack. Some important information from the study on plume dispersion and its effect on aircraft was as follows: • Creating a dispersion model to establish the plume velocity and temperature after the plume leaves the stack based on meteorological data and exhaust stack parameters. • Ability to account for multiple stacks which can cause merged plumes and enhance buoyancy. • Turbulence model to account for the velocity fluctuations or turbulent gusts of the plume over time. • Aircraft Response Model to determine the effect the plume has on an aircraft flying over it. 106FAA, “Expanded Model for Determining the Effects of Vertical Plumes on Aviation Safety,” September 2012. 107DeVita, P., Personal Communication with C. Ford, Harris Miller Miller & Hanson Inc., 2010. 108DeVita, P., Personal Communication with M. Rosenblum, Harris Miller Miller & Hanson Inc., 2012.

55 • Establish Turbulence categories and vertical acceleration and turbulence intensity for the plume velocity and potential impact to aircraft. • Establish upset criteria to determine if aircraft upset could occur. • Probability of Risk of how often the event could occur. • Helicopter Risk to establish a threshold for maximum tem- peratures and oxygen content of the plume. 3.4.2.5 Other Characterization Tools Modeling is also used to evaluate impacts from cooling towers, most notably the Seasonal Annual Cooling Tower Impact (SACTI) model. The SACTI model was developed by Argonne National Laboratory and University of Illinois in the 1980s and provides seasonal and annual impacts from cooling towers. The model is capable of predicting frequency (including lengths and heights) of visible cooling tower moisture plumes along with the potential hours of fogging and icing. Currently, FAA has no standards for regulating visual impacts from thermal plumes. 3.4.3 Managing Plume Impacts While there are several sophisticated modeling tools avail- able for predicting the characteristics of a plume and poten- tial influence on aircraft, there are no specific federal U.S. standards or guidelines to evaluate if the impact is significant. However, guidelines developed in Australia and general FAA guidance offer some strategies for managing potential plume impacts and minimizing impact. 3.4.3.1 Australia CASA Plume Velocity Criterion In response to a proposal to construct a simple cycle gas turbine at the end of a runway in the early 1990s, Australia’s CASA began evaluating potential impacts of new exhaust stacks near airports. CASA was concerned that the vertical velocities from the exhaust have the “potential to damage and/or affect the handling characteristics of an aircraft in flight.” To address thermal plume impacts, the CASA issued an AC in June of 2004 to develop guidelines for conducting plume rise assessments for exhaust plumes that trigger sig- nificance criterion.109 The guidance established that “exhaust plumes with a vertical gust in excess of the 4.3 meters per second (m/s) threshold may cause damage to an aircraft air- frame, or upset an aircraft when flying at low levels.” Typical low-level operations consist of approach, landing, take-off, search and rescue, and low-level military maneuvers. The origin of this threshold is unknown and CASA was unable to verify the source of the threshold.110 However, CASA had used the 4.3 m/s as a significance criterion on past power projects prior to issuing the AC. The 4.3 m/s is not a standard, but rather a trigger for further plume assessment in order to evaluate the potential hazard to aircraft operations. The CASA assessment takes into account the location of the plume relative to the airport and active airspace, stack exhaust parameters, and local meteorology. The plume assessment consists of a screening and a more refined approach. The screening approach assumes calm wind conditions, which are conservative, resulting in worst case conditions. The guidance provides for a more refined plume assessment to include local meteorology and complex numerical modeling of the thermal plume. Using the local meteorology allows for the determination of the frequency distribution of the plume at the critical height (i.e., the height of the plume where the plume velocity is 4.3 m/s or greater) over a year of meteorological conditions. The frequency dis- tribution of the thermal plumes at the critical height is used to evaluate if there could be a potential hazard to aircraft safety and how often the conditions could exist over the year. The guidance is not limited to single stacks, but also includes a methodology for analyzing the impact from multiple stacks and merged plumes. Multiple exhaust stacks located near each other could have individual plumes that merge and form a higher buoyancy combined plume, which could enhance the vertical velocities of the plume and enhance the gust of the plume or turbulence. If the plume assessment identified a potential hazard, the original guidance generally managed any potential risks by directing pilots to avoid flying over the exhaust stack. The CASA guidance was recently updated in 2012 to include a new critical plume velocity criterion of 10.6 m/s along with a revised plume assessment methodology and new mitigation options if the plume assessment shows a potential hazard to aircraft. The new 10.6 m/s criteria is based on Airservices Australia’s “Manual of Aviation Meteorology”111 and defines severe turbulence as vertical wind gusts in excess of 10.6 m/s which may cause a momentary “loss of control.” The new AC provides criteria to determine when CASA may take action during IFR and VFR conditions. However, these are not explicitly defined thresholds and CASA may include other factors similar to the original guidance, such as the height at which the aircraft may fly over the exhaust plume and prob- ability of occurrence. The plume assessment methodology under the new guidance is similar to the old guidance but has standardized the methodology to allow for consistent 110DeVita, P., Email to Anna Henry, CASA Airspace Specialist, Harris Miller Miller & Hanson Inc., June 5, 2013. 111Airservices Australia, “The Manual of Aviation Meteorology,” 2003. 109Australia Civil Aviation Safety Authority (CASA), “Guidelines for Conducting Plume Rise Assessments,” AC 139-05(1), November 2012.

56 and reliable review of the plume assessment using computer- based modeling. The assessment should evaluate the height at which the plume velocity from the exhaust stack reaches the average vertical velocity criterion of 4.3 m/s along with the new critical plume velocity criterion of 10.6 m/s. To put these two thresholds into some perspective, the 4.3 m/s is equivalent to the wind blowing at 9.61 mph (or 8.4 knots) and the 10.6 m/s threshold is equivalent to a wind blowing at 23.7 mph (or 20.6 knots). Using the Beaufort Wind Scale,112 the 4.3 m/s is characterized under the Beaufort scale as a gentle breeze described as leaves and small twigs constantly moving. The 10.6 m/s is characterized as a fresh breeze described where small trees in leaf begin to sway. The CASA guidance pro- vides new mitigation options, such as inserting a symbol and height on aviation charts to denote awareness of the plume rise, designation of a danger area on aviation charts to alert pilots to the plume hazard, or designation of a restricted area on the chart to alert pilots not to fly over the area. It also denotes that CASA may recommend against the development of the project if mitigation cannot be implemented. Absent other available review criteria, regulatory agencies outside of Australia have used the CASA guidance in evalu- ating potential impacts. The California Energy Commission (CEC) has applied the CASA 4.3 m/s threshold to new power plant applications in considering potential thermal plume impacts to aircraft. For the proposed Blythe Solar Power Plant, the CEC decision required that air nautical charts be updated to reflect the potential hazard. For the Ivanpah Solar Power Plant, the CEC decision restricted aircraft to flying no lower than 1,350 ft. over the facility. 3.4.3.2 MITRE Study Guidance Since severe turbulence can cause large and abrupt changes in altitude and/or attitude, thereby causing the pilot to tem- porarily lose control of the aircraft, a MITRE study concluded that the potential to create more than a 1G vertical accelera- tion from the plume velocity on an aircraft was established as a safety threshold. Potential gusts from plume exhaust that could cause a peak vertical acceleration of greater than 1G should be avoided. The study also looked at the aircraft upset standards and upset criteria based on the FAA’s Airplane Upset Recovery Training Aid.113 While there were many conditions that could cause aircraft upset including pitch attitude and inappropriate airspeeds, the study focused on the bank angle upset condition in the roll response model as the criterion for assessing aircraft upset from the plume gusts and was incorporated into the Plume Hazard Model. As the pitch of the aircraft increases, the potential increases for aircraft upset conditions to occur. In the case of thermal plumes, the potential for turbulence on the aircraft from the plume could cause the aircraft to increase its bank angle and cause an upset condition in flight. Using the FAA criteria and the roll response model, the study considered as a significance criteria that an aircraft upset condition could occur if the bank angle exceeds 45 degrees. The study included the TLS of 1.0 × 10-7 that was consid- ered the acceptable level of risk based on the 2006 FAA Safety Risk Analysis and was based on the ATO SMS Manual114 qualitative criteria for risk. To put this into perspective, there are five likelihood definitions in the ATO Manual ranging from “frequent” to “extremely improbable,” with corresponding probability of occurrences ranging from 1 × 10-3 for “frequent” occurrences to 1.0 × 10-9 for “extremely improbable” occur- rences. The TLS was determined to be one chance in 10 million of a fatal accident occurring. The study found that the accident or incident rate of overflights of exhaust plumes was deter- mined to be one chance in 1 billion or less. The 1.0 × 10-7 TLS used in the MITRE and FAA Safety Risk Analysis represents a remote likelihood of an event equivalent to an occurrence once every year. The TLS was based on historical data and gust amplitude. The study highlights that the TLS of 1 × 10-7 risk level is very small. However, the MITRE report did note that while the risk was lower than the TLS for an aircraft accident caused by the plume, it did denote that there was potential for aircraft upset to occur when flying over the immediate vicinity of the plume. 3.4.3.3 FAA Guidance to Pilots The FAA under the TERPS requires that approach pro- cedures are designed to maintain certain vertical margins between fixed objects (e.g., exhaust stacks) and aircraft by 1,000 ft. within the initial approach fix, 500 ft. within the intermediate fix, and 250 ft. within the final approach. The AIM was updated in 2010 at the request of numerous stakeholders (e.g., Aircraft Owners and Pilots Association [AOPA]) to include visible and invisible plumes and high- light their potential effect on aircraft and pilots. AIM Chapter 7-5-15 was updated to include a warning to pilots to avoid flight near thermal plumes including smoke stacks and cool- ing towers. A NOTAM is typically issued by a government agency to alert pilots to potential hazards along the flight route or at a specific location that could affect the safety of the aircraft. The FAA issued a NOTAM on October 8, 2004, which states as follows: “In the interest of national security, and to the 112U.S. National Oceanic and Atmospheric Administration (NOAA), “Beaufort Wind Scale”: http://www.spc.noaa.gov/faq/tornado/beaufort.html. 113FAA, “Airplane Upset Recovery Training Aid, Revision 2,” 2008: http://www. faa.gov/other_visit/aviation_industry/airline_operators/training/media/AP_ UpsetRecovery_Book.pdf. 114FAA, “Air Traffic Organization: Safety Management System Manual, Version 2.1,” 2008.

57 extent practicable, pilots are strongly advised to avoid the air- space above, or in the proximity to such sites as power plants (nuclear power plants, hydroelectric, or coal); dams; refineries; industrial complexes; military facilities; and other similar facilities.”115 This NOTAM was intended to protect power plants from potential security breaches by piloted aircraft, in response to the September 11, 2001, terrorist attacks. Still, this guidance represents an operating restriction to aircraft in relation to energy facilities and, therefore, bears mentioning. 3.4.4 Helicopters The potential impacts on helicopters from plumes repre- sent a separate case, which was also considered in the MITRE study. For helicopters, the hazards are not necessarily from the turbulence created by the plume but from the high tem- peratures and low oxygen content of the plume. Helicopters have maximum operating temperatures and minimum oxy- gen content required for safe operation. Elevated tempera- tures and/or low oxygen content can cause the engines to fail. These conditions are significant concerns around exhaust stacks, especially from flares burning flammable gases from pressure relief valves near gas wells and offshore oilrigs (see Section 3.3). Based on a review of a variety of helicopter specifications, the MITRE study established a maximum operating tem- perature threshold of 52°C. Plume temperatures above 52°C were considered unsafe for helicopter operations. The Plume Hazard Model has the ability to estimate the plume tempera- ture with height, allowing helicopter operators to evaluate not only the turbulence area but also the temperature of the plume and assess the relative safety levels above the stack. In addition to the plume temperature, the oxygen concentration of the plume can also be estimated. Using the FAA report on jet fuel, it was found that 12 percent oxygen is required to ignite the fuel at altitudes below 10,000 ft. The 12 percent oxygen threshold was considered the minimum oxygen threshold requirement for the study and one of the variables used in the model. By assuming a worst case scenario of 0% oxygen plume content from the stack, and a typical value of 20.9 per- cent oxygen content in the air, the areas of reduced oxygen above the stack can be estimated in the model and compared to the 12 percent minimum oxygen criteria identified by FAA (see Figure 3.35). 3.4.5 Case Study: Eastshore Energy Center The Eastshore Energy Center was a proposed 115.5 MW peaking power plant located in the city of Hayward, California, approximately 1 mile from the Hayward Executive Airport. The proposed plant consisted of 14 natural gas-fired engines each with a 70-ft. exhaust stack. There were numerous con- cerns about the facility including air quality, noise, pub- lic health, global warming, property values, and aviation safety. The CEC evaluated the project for years and eventu- ally denied the application to build the facility based on deficiency in five areas,116 including the following related to aviation: • The facility would cause a significant cumulative public safety impact on the operations of the nearby Hayward Executive Airport by further reducing already constrained air space and increasing pilot cockpit workload. • The thermal plumes from the facility would present a significant public safety risk to low flying aircraft during landing and take-off maneuvers because of the close prox- imity of the Hayward Airport. • The facility would be inconsistent with the city of Hayward’s Airport Approach Zoning Regulations and incompatible with the Alameda County Airport Land Use Policy Plan. It should be noted that the FAA issued a No Hazard Deter- mination for the 14 stacks on May 15, 2007, and the CEC still rejected the project for the reasons stated above. The nearby Russell Energy Center, also in Hayward, is a proposed 619 MW power project located approximately 1.5 miles from 115FAA, Notice to Airmen (NOTAM), FDC 4/0811. Figure 3.35. Criteria for helicopter flight near plumes. 116California Energy Commission (CEC), “Final Decision: Eastshore Energy Center,” Sacramento, 2008: http://www.energy.ca.gov/2008publications/CEC-800- 2008-004/CEC-800-2008-004-CMF.PDF

58 Hayward Executive Airport. The two 145-ft. exhaust stacks were evaluated by the FAA and a No Hazard Determination was issued for the project. The CEC evaluated the proposed Russell Energy Center and approved the project’s Applica- tion for Certification. The Russell Energy Center commenced operation in August of 2013. 3.4.6 Lessons Learned The issue of thermal plume impacts on small fixed-wing aircraft and helicopters represents another example of a non- physical intrusion of airspace that is difficult to measure and therefore difficult to establish significance criteria. As stated in the MITRE report conclusion section, “while it is unlikely that an aircraft will reach upset criteria, there is a definite risk of light aircraft experiencing severe turbulence within the TLS as they fly above an exhaust plume emitted from a power plant or other industrial facility in certain weather conditions.” There are numerous documented incidents of pilots reporting turbulence when flying over exhaust stacks. However, no specific regulatory criteria have been developed due to the difficulty of characterizing impacts. Australia’s CASA identified the need for plume hazard evaluations and developed a methodology through an Advisory Circular in 2004, which was recently updated in 2012 to account for new criterion to address “severe turbulence” and “loss of control” to an aircraft. Since the CASA guidance is the only formal reg- ulatory criteria in use, it will likely be used by other regulatory bodies when evaluating potential effects. As power plants are large structures visible in the landscape, the clearest guidance is to avoid flying over power plants especially when flying at low altitudes and be aware of potential turbulence in the area from exhaust stacks as this turbulence can be either visible or not visible depending on weather conditions. 3.5 Electricity Transmission Infrastructure 3.5.1 Research Context Electricity transmission infrastructure, which is composed of transmission towers, electrical lines, and associated facilities, represents one of the largest interconnected structures in the world. High voltage transmission (230 kilovolts and greater) covers more than 200,000 miles in the United States.117 As new energy generation sources like renewables are developed far from population centers, new transmission lines are required to deliver the electricity to users. Transmission lines cross- ing more remote locations can present new impacts to local populations including potential effects on airspace safety. Electricity transmission impacts on aviation are primar- ily related to physical impacts. Since transmission lines are an essential component of delivering energy to consumers, they are ubiquitous throughout the landscape. The degree of potential impact is correlated with the amount of power being delivered and the size of the infrastructure. Large trans- mission towers that are several hundred feet tall are necessary to hold up large high voltage transmission lines. These large structures are comparatively closer to the energy generation facility. Advancements in transmission technology are cre- ating more efficient delivery with less power loss over long distances (i.e., line losses) making long-distance transmission more economical. The utility poles and power lines decrease in size as power is delivered to businesses and people. It is more common for the public to request that transmission lines be buried for aesthetic reasons though utilities usually try to avoid burial except where necessary due to the increased cost of doing so. Existing power lines are common obstructions near air- ports. Many of these lines are either long-lived, were upgraded over time without input from airport and aviation stake- holders, or have become obstructions as airports have expanded. It is also likely that utility poles adjacent to remote air- ports have not been appropriately inventoried as potential obstructions.118 3.5.2 Characterizing Impacts 3.5.2.1 Physical Obstructions Electric transmission lines and the towers that support them can rise high enough to impact airspace. The transmission towers that support the electrical lines are the tallest part of the facility. The towers are typically constructed of a lattice steel 118Barrett, S., Personal Communication with Robert Knowles, Renewable Energy Massachusetts, about a proposed solar project near Fitchburg Airport (Massachusetts), Harris Miller Miller & Hanson Inc., July 10, 2013. 117Edison Electric Institute, “Transmission”: http://www.eei.org/issuesandpolicy/ transmission/Pages/default.aspx CRITICAL RESEARCH NEED—Electricity Transmission Infrastructure Identify new transmission projects and collect information to assess if the projects have affected airspace, in addition to collecting more informa- tion on the aviation safety impacts from existing electricity infrastructure.

59 frame and average between 50 and 180 ft. tall depending on the size of the electrical line being carried among other factors.119 However, transmission towers exist that are as tall as 1,100 ft.120 During the project review process, if the FAA is sufficiently notified, it may comment on potential effects of a proposed power line project and request consideration of alterna- tives to avoid a potential impact. Alternatives might include a different route for the transmission line away from air- space receptors, lower structures, or burying the power lines underground. If none of these options is feasible, the FAA could determine that the project is not an airspace hazard if appropriate lighting and marking is included, or it could determine that it is a hazard and consider potential modifica- tions to approach procedures. It is customary that transmis- sion infrastructure near airports has lighting and/or marking. The FAA’s AC 70/7460-1K, “Obstruction Marking and Light- ing,” provides guidance on the types of lighting and markers that meet FAA requirements. 3.5.2.2 Communications Systems Interference Communications systems interference results when a struc- ture produces a physical or electrical barrier to communica- tions facilities. Such facilities associated with the NAS include radars, ILS, and NAVAIDs. Electric utility infrastructure can produce electromagnetic interference (EMI). Devices employ- ing solid-state switching can place high levels of impulse cur- rent and voltage onto the electric wiring, ground conductors, and other metal components associated with a source. These impulses pass through the transformer and onto the con- ductors of an overhead distribution line providing electric power to the facility. Interference radiating from the build- ing conductors and the overhead power line conductors of a distribution line associated with such a facility can result in interference to radars located within line-of-sight of the overhead lines. In addition, corona interference can occur from transmission lines operating at high voltages (typically from 69 to 750 kV, and in some special cases up to 1 MV). A corona can develop as the breakdown of air at very small and sharp metal protrusions that form on a power line or switching substation. When these small protrusions are removed, the corona noise will disappear. As described in “Procedures for Handling Airspace Matters,” the FAA is “authorized to establish, operate, and maintain air navigation and communications facilities and to protect such facilities from interference. During evaluation of structures, factors that may adversely affect any portion or component of the NAS must be considered. Since an EMI potential may create adverse effects as serious as those caused by a physi- cal penetration of the airspace by a structure, those effects must be identified and stated.” (The procedures include some specific guidelines for power lines, which are outlined in Table 4.5.) 3.5.3 Managing Impacts Many transmission line projects proposed near airports have filed Form 7460, which triggers aeronautical studies by the FAA to ensure that impacts to airspace are avoided. However, the project proponent may not always be aware of the need to file with the FAA. Projects subject to NEPA review, or similar state environmental reviews, will include a process whereby potential effects on transportation systems must be assessed and the FAA and local airports will be consulted. In other cases, the airport may become aware of a proposed project and request that the applicant consult with the FAA about potential impacts. Project experience offers the best information on how the impacts of transmission lines can be managed. There have been recent reports of large transmission lines that have been constructed without obtaining FAA approval. A post-construction analysis of airspace impacts conducted by the FAA may determine that the project presents a hazard to air navigation. In such instances, the FAA has three potential options: (1) require the dismantling to the violating section of line, (2) place lighting and other facilities on the line, and (3) change the approach minimums. A 12.9 mile, $21 million 115-kV power line project was constructed in November 2010, which runs as close as ½ mile northwest of the runway at Blake Municipal Airport in Delta, Colorado. It was determined that the engineers mis calculated the latitude and longitude they inserted into the FAA’s “Notice Criteria Tool,” an online program that proponents can use to assess if their project may be subject to FAA review. The transmission company had obtained a county permit that was conditioned upon receiving all federal and state approvals. The FAA completed its aeronautical study after the fact and determined that the power lines represent an air navigation hazard, though it has no authority to require that the lines be moved. Only the Delta County Commission can exer cise that right. The power company agreed to lower the lines to minimize impacts. Power lines can also present obstacles to airport expan- sion projects. The extension of the DeKalb County (Georgia) Airport’s runway to 7,000 ft. required the burial of existing power lines to avoid an airspace obstruction. The cost of burial in this case was approximately $1 million, paid for by the FAA as part of the expansion project. Additionally, power lines are 119International Finance Corporation (IFC), “Environmental Health and Safety Guidelines for Electric Power Transmission and Distribution,” April 30, 2007: http://www.ifc.org/ifcext/enviro.nsf/AttachmentsByTitle/gui_EHSGuide lines2007_ElectricTransmission/$FILE/Final+-+Electric+Transmission+and+ Distribution.pdf. 120One such tower is produced by Alimak Hek: http://alimakhek.com/.

60 listed as an obstruction to Runway 36 at Waterbury-Oxford Airport in Connecticut.121 3.5.4 Airspace Case Study: Texas Competitive Renewable Energy Zones (CREZ) The Electric Reliability Council of Texas (ERCOT), estab- lished in 1975 to oversee the electric and telecommunications industries in Texas, was directed by legislation passed in 2005 to develop Competitive Renewable Energy Zones (CREZ) in the state. A CREZ is a geographic area with optimal con- ditions for the economic development of wind power genera- tion facilities. Five CREZ areas were established and specific transmission projects were identified that would deliver 18,500 MW of wind power from west and north Texas to the more densely populated parts of the state. Figure 3.36 shows the location of the CREZ areas relative to population centers in Texas. As part of this project, the Central CREZ was visited. There has already been a high density of wind power devel- opment in the area including the Horse Hollow wind project, which is referred to as the largest wind farm in the world (see Figure 3.37). This high plains area southwest of Abilene was viewed in the field from U.S. Route 277 and State Route 153. According to the American Wind Energy Association, there are 1,863 wind turbines in this area.122 New transmission infrastructure that has been constructed as part of the CREZ project was also identified in the field. The Scurry Transmission Project, shown in Figure 3.38, includes Figure 3.36. Location of Competitive Renewable Energy Zones (CREZ) in Texas. 121Aircraft Owners and Pilots Association (AOPA), Airports listing for Waterbury- Oxford Airport: http://www.aopa.org/airports/KOXC. 122As researched on the AWEA website, accessed August 30, 2013: http://www. awea.org

61 Figure 3.37. Horse Hollow wind farm southwest of Abilene. Figure 3.38. Recently constructed transmission lines as part of the CREZ project. these transmission lines identified perpendicular to State Route 70 just north and west of Sweetwater, Texas. After the site visit, airports were contacted in the area between Sweetwater and Lubbock, where the recently constructed transmission line was located. Seven airports were identified. Three of the airports were determined as no longer operational based on satellite imagery and of the four remaining, two had non-operational telephone numbers. The remaining two were contacted and staff at Hamlin Municipal Airport (14F) in Hamlin and Avenger Field Airport (SWW) in Sweetwater both stated that they were not aware of any airspace problems associ- ated with the new transmission lines. 3.5.5 Lessons Learned The topic of transmission line development and airspace impact illustrates a few key points. First, as transmission lines have been constructed in the same manner for over 100 years (i.e., power lines attached to utility poles), many such obstruc- tions exist near airports. Aircraft are alerted to these obstruc- tions when reviewing information and procedures for specific airports and some areas are being mitigated over time. A variety of mitigation options are available to address existing problem sites, including making physical modifications (e.g., lowering the height or burying the lines), placing lights or signal ball markers, or increasing minimum altitude standards. In addition, some transmission projects may not be reviewed by the FAA or aviation stakeholders, so those obstructions may not be identified until project construction occurs and impacts are observed. This suggests how important it is that airports and local stakeholders maintain awareness of electric- ity transmission development projects in the area of airports and that they refer any potential issues to the FAA’s Regional Office or ADO.

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TRB’s Airport Cooperative Research Program (ACRP) Report 108: Guidebook for Energy Facilities Compatibility with Airports and Airspace describes processes to plan, develop, and construct energy production and transmission technologies at and around airports. The guidebook emphasizes aviation safety practices in order to help ensure a safe and efficient national air system while still helping to meet U.S. domestic energy production needs.

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