Evaluating Airfield Capacity (2012)

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88 Subsequent Uses of Airfield Capacity Estimates Airfield capacity alone is a very useful performance metric, but its real value can only be realized by comparing it with existing and future demand for aircraft operations in subsequent applica- tions. Many and diverse applications of airfield capacity information are available in the aviation industry. This chapter briefly describes a few of the most common applications of airfield capac- ity information in aviation planning and decision making, as follows: • Making demand-capacity comparisons • Providing data for environmental analyses • Informing benefit-cost analysis (BCA) • Balancing airfield capacities with passenger terminal and landside facility capacities • Demand/congestion management (FAA) • Benchmarking with other airports • Measuring the progress of the Next Generation Air Transportation System (NextGen) • Input to models for estimating aircraft delays • Application of airfield service volumes and aircraft delay thresholds • Defining and measuring aircraft delay and airport capacity thresholds Making Demand-Capacity Comparisons Airfield capacity estimates are commonly used to assess whether (1) existing airfield capacity will be sufficient to meet existing or forecast demand, and (2) proposed capacity enhancements will enable the airfield to meet forecast demand. Such demand-capacity assessments typically are made as part of airport master planning and system planning studies, which are typically fol- lowed by environmental reviews and assessments of the recommended capacity enhancements. Comparing a capacity estimate with demand can indicate the potential performance of an airfield and the need for additional capacity. The ultimate capacity of an airport is largely deter- mined by the capacity of its airfield. Capacities of other airport components (taxiways, gates, the terminal, and access roadways) are rarely the limiting factors of an airport system. Balancing airfield capacity with the capacities of other airport components is discussed later in this chapter. Airfield capacity can be compared with demand on an hourly and an annual basis, as dis- cussed below. Hourly Airfield Demand-Capacity Comparisons Evaluating hourly demand versus hourly capacity is the first step in a demand-capacity com- parison. In the United States, the typical demand level selected for such hourly demand-capacity comparisons is the peak hour of the average day, peak month (ADPM). Making comparisons C h a p t e r 6

Subsequent Uses of airfield Capacity estimates 89 with the ADPM peak hour should ensure that sufficient capacity is provided for most days of the year, recognizing that there may be periods during very busy days when delays, congestion, and queuing will occur. In some situations, selection of the ADPM peak hour is not appropriate for measuring demand and could result in an underestimation of demand at peak times. In these cases, it may be appropri- ate to use a design-hour volume based on a specific percentile (e.g., 90th or 95th percentile) of the busiest hours of the year. The concept of design-hour volume for aircraft traffic is similar to that of design-hour volume as used for other modes of transportation. For example, in highway design, the demand during the 30th busiest hour of the year is typically used as the design-hour volume. Hourly throughput capacity can be estimated using any of the capacity analysis methods discussed in this guidebook. If peak-hour demand typically consists mostly of arrivals or mostly of departures, it may be appropriate to compare that demand to the airfield capacity for the corresponding per- centage of arrivals (e.g., if peak-hour demand tends strongly toward more departures, then a 30% arrival capacity would be appropriate for comparison; if peak-hour demand tends strongly toward more arrivals, then a 70% arrivals capacity would be appropriate for comparison). The maximum sustainable throughput capacity typically is close to or higher than the high- est observed actual flow rates on the airfield, but it can be exceeded during certain busy hours of the year. Estimates of maximum sustainable throughput capacity are based on assumptions regarding average aircraft approach speeds, minimum separation requirements (computed as the minimum required separations plus a buffer), average runway occupancy times, and either average or peak-hour aircraft fleet mix. During certain hours of the year, conditions may differ from these assumed average values, which can result in actual observed through- put rates that are greater than or less than the estimated maximum sustainable throughput capacity. Many applications for airfield capacity estimates require a simple comparison of hourly air- field capacities with existing or forecast peak-hour operations. Again, any level of modeling sophistication could produce estimates of hourly runway capacity for purposes of comparison with estimates of peak-hour demand. If this is the only application of such airfield capacity esti- mates, however, then the less sophisticated models typically are adequate. Figure 6-1 shows an example of an hourly demand-capacity comparison. Source: LeighFisher. Capacity off Base Case Capacity after Runway Removal Peak-Hour Demand Figure 6-1. Example of a comparison of peak-hour demand with hourly airfield capacity.

90 evaluating airfield Capacity Annual Airfield Demand-Capacity Comparisons For the majority of airports, comparing an estimate of annual airfield capacity with estimates of annual demand for aircraft operations is sufficient to determine the need for airfield improvements. The annual capacity of an airfield does not equal hourly capacity multiplied by 24 hours in the day and 365 days in the year. Capacity provided during hours when there is little or no demand is not relevant. Estimates of annual capacity must account for variations in demand over the hours of the day and months of the year. Consequently, ASV was developed as an estimate of an airport’s annual capacity to accommodate aircraft operations considering the variations in demand. ASV is not a hard ceiling number; rather, it is intended to be interpreted as the number of actual annual aircraft operations above which additional increases in aircraft operations would result in disproportionate increases in average aircraft delays. In calculating ASV, a weighted average of the hourly capacities over the year, computed using formulas specified in FAA’s AC 150/5060-5, Airport Capacity and Delay (the AC), is expanded to an annual number by multiplying by the ratio of ADPM operations to peak-hour operations, and the ratio of annual operations to ADPM operations. Thus, ASV is calculated using the fol- lowing formula: ASV C D Hw= × × where Cw = the weighted average hourly capacity of the airfield, D = the ratio of annual to ADPM demand, and H = the ratio of ADPM demand to peak-hour demand. Any level of modeling sophistication could be used to estimate hourly runway capacities under different runway uses and weather conditions, to estimate a weighted hourly capacity, and, subsequently, to estimate ASV. Such hourly capacities typically are referred to as balanced hourly airfield capacities or equivalent 50% arrivals hourly airfield capacities. The ratios for D and H should be calculated using data from airport records or publicly avail- able sources on air traffic demand pattern. When demand data are not available, the recom- mended default values in the AC can be used. The D factor measures seasonal variation in monthly demand, where a value of 365 would indicate that all months have the same demand. Very low D values (e.g., values less than 300) would indicate substantial seasonality typical of vacation destinations. The H factor measures variation over the hours of the day, where a value of 24 would indicate that all hours of the day have the same demand. Much lower H values (e.g., values less than 12) would indicate substantial peaking in demand over the hours of the day. Annual capacity estimates can inform the number of operations at which new airfield infra- structure would be needed to accommodate demand. Figure 6-2 shows an example of comparing forecast annual demand to estimated ASV for different airfield development scenarios. Ideally, airfield capacity would be increased incrementally through new infrastructure or procedures to accommodate forecast demand. Demand-capacity comparisons such as those described above are most often made as part of a master plan or system plan to determine whether further analysis is needed. Identified capacity shortfalls, driven by growing demand, will require additional runways or taxiways, or improved air traffic control procedures. The capacity analysis forms the basis for developing and evaluating alternatives, and for selecting the preferred alternative to best accommodate future demand. At small airports, airfield capacity typically exceeds expected demand by a wide margin; therefore,

Subsequent Uses of airfield Capacity estimates 91 reporting the estimated airfield capacity in a master plan or system plan will most often satisfy any requirements for airfield capacity analysis and facility requirements. For airport master planning and system planning, capacity estimates are typically required for a wide variety of facility and procedural alternatives. For preliminary screening of alternatives, analytical models or spreadsheets are usually the preferred methods for evaluating airfield capac- ity. Once the alternatives have been screened down to a manageable number for detailed analysis, airfield simulation analysis may then be justified to distinguish among the final alternatives. Providing Data for Environmental Analyses Airfield capacity estimates are important inputs to certain environmental analyses, such as (1) air quality analyses, where changes in queuing locations or times could result in a change in the location and level of emissions; and (2) aircraft noise analyses, where changes in runway use or fleet mix on a runway could change noise exposure patterns. In some cases, less sophisticated models are adequate to evaluate capacity differences between alternative airport improvements, but a more sophisticated model may be needed to provide the information needed for the envi- ronmental evaluation models used in the National Environmental Policy Act (NEPA) analysis process. Demand-capacity comparisons made for environmental analyses use average annual day (AAD) instead of ADPM because AAD is the demand metric used for aircraft noise exposure analyses. Informing Benefit-Cost Analysis A BCA is required for airport capacity projects that exceed $10 million in discretionary grants from FAA. Capacity projects studied in BCAs include new or extended runways, taxiways, aprons, or hold pads. The monetization of benefits typically revolves around translating the expected capacity increase into a quantifiable benefit, whether the project is expected to reduce passenger or aircraft delays, improve schedule predictability, or enable larger aircraft. Source: LeighFisher. A n n u a l A ir T ra ff ic M o ve m e n ts ( A T M s) Figure 6-2. Example of an annual demand-capacity comparison.

92 evaluating airfield Capacity Balancing Airfield Capacities with Passenger Terminal and Landside Facility Capacities At most airports, the capacity of the airfield system determines the ultimate capacity of the airport. However, prudent planning requires that airfield capacity be balanced with the capacities of other airport components, such as the terminal complex, ground access roadways, and the cargo complex. This balancing is usually accomplished in the facility requirements portion of an airport master plan. Figure 6-3 shows a sample chart comparing annual capacity in terms of total annual passengers using the various airport components. In this case, the access roadways and airfield have the highest annual capacities, whereas the rental car facilities and passenger security screening facilities have the lowest annual capacities. This type of chart is sometimes referred to as a stoplight chart because the colors green, yellow, and red are used to indicate the degree of demand saturation or congestion. Demand/Congestion Management (FAA) Fan and Odoni define demand-management measures as any set of administrative or eco- nomic measures, or combinations thereof, aimed at balancing aircraft operations demand with airport capacities.1 These measures typically are intended to limit the number of peak- hour flights through slots or auctions so that aircraft delays do not become excessive. The term congestion management has been widely used recently, sometimes in conjunction with demand management, which sometimes is expressed as congestion management by demand- management measures. Source: LeighFisher. Figure 6-3. Stoplight chart comparing annual capacities of various airport components. 1T. P. Fan and A. R. Odoni, “A Practical Perspective on Airport Demand Management,” Air Traffic Control Quarterly, Vol. 10, No. 3, pp. 285–306, 2002.

Subsequent Uses of airfield Capacity estimates 93 Such demand-management measures in the United States were initiated in 1968 when FAA issued the High Density Traffic Airports Rule (HDR) (14 CFR Part 93 Subpart K), to reduce delays at five congested airports—John F. Kennedy International, LaGuardia, New- ark Liberty International, Chicago O’Hare International, and Ronald Reagan Washington National airports—and such measures have continued to be proposed in one form or another in various legislative and administrative rulemakings to the present day. Nearly all of these demand-management initiatives have used estimates of airfield capacity as the basis for limit- ing operations at very congested airports. Various airfield capacity metrics have been used over the years for setting limits on the number of slots allowed in demand-management initiatives at congested airports. These metrics have generally involved estimates of average hourly airfield capacity that are intended to control the level of aircraft delays expected to occur at a congested airport. Airfield capacity limits also have been expressed in terms of maximum permitted operations in 15-minute intervals, and certain limits have been expressed in terms of the maximum numbers of flights permitted by certain classes of aircraft or air service. Up to now, however, no metric has been universally accepted for use in demand-management measures, and the recommended metrics have been typically site- specific and restricted by U.S. law. Benchmarking with Other Airports FAA’s Airport Capacity Benchmark Report 2001 and Airport Capacity Benchmark Report 2004 were prepared by MITRE Corporation using the FAA Airfield Capacity Model (ACM) along with interviews and data on airport arrival rates (AARs) and airport departure rates (ADRs) provided by local air traffic specialists. In 2011 and 2012 MITRE updated the Airport Capacity Benchmark Report using its runwaySimulator model, which is described in Chapter 4. As this guidebook was being prepared for publication, the 2012 benchmark capacities were anticipated but had not yet been released to the public. Airport operators also have recently prepared a variety of benchmarking studies. Among the factors considered in these benchmarking studies are airfield capacity and aircraft delay. For this purpose, airport operators need a metric that is readily available for their own airport and for comparable airports. For purposes of comparing airfield capacities, FAA’s Airport Capacity Benchmark Reports are a good source of capacity estimates for airport operators. Measuring the Progress of NextGen FAA is developing a set of NextGen performance assessment metrics based on the International Civil Aviation Organization (ICAO) key performance areas (KPAs). ICAO has defined a capacity KPA as a measure of the ability of the national airspace system, an airspace sector, a metroplex, or an airport to accommodate demand. The capacity KPA has been defined in terms of both the actual throughput in peak demand periods and the maximum throughput capability in a specified time interval. The main differ- ence between these two definitions is that actual throughput can be measured by direct observa- tion, while maximum throughput capability must typically be calculated using available data and models that reflect the rules and procedures that determine capacity. Actual throughput can be used to estimate and validate maximum throughput capability, and also to determine the degree to which the maximum throughput capability is being used. For the maximum throughput capability metric applied to airports, FAA expects to use its AARs and ADRs, the maximum number of landings and takeoffs that can be accommodated at

94 evaluating airfield Capacity an airport under a given set of operating conditions. The FAA Pilot/Controller Glossary defines these rates as follows: Airport Arrival Rate (AAR): A dynamic input parameter specifying the number of arriving aircraft that an airport or airspace can accept from the Air Route Traffic Control Center per hour. The AAR is used to calculate the desired interval between successive arrival aircraft. Airport Departure Rate (ADR): A dynamic parameter specifying the number of aircraft that can depart from an airport and that the airspace can accept per hour.2 AARs and ADRs are calculated using a combination of controller judgment, analyses of actual throughput data, and airfield capacity modeling. As NextGen procedural and operational improvements are introduced, these AARs and ADRs will be recalculated to reflect the improved capabilities. FAA expects to use these updated AARs and ADRs as high level metrics for the post- implementation measurement of the effects of NextGen improvements on airfield capacity. AARs and ADRs are provided by the Air Traffic Control System Command on a daily basis for a set of 77 airports tracked by FAA’s Aviation System Performance Metrics (ASPM) database. The AARs and ADRs are based on time of day, flight schedules (from OAG), available staff to handle traffic, weather conditions (ceiling and visibility), and runway configurations. Input to Models for Estimating Aircraft Delays Airfield capacity estimates often are input into models used to estimate aircraft delays. Usually, hourly runway capacity estimates appropriate for this purpose would be obtained using Level 3 or Level 4 airfield capacity models. Average aircraft delays can then be estimated using an analyti- cal model that compares hourly demand with hourly capacity, typically over a 1-year period. The calculation of delay within such an analytical model usually is based on queuing theory models or equivalent cumulative demand versus capacity comparisons. One such model is the FAA Annual Delay Model. In addition, various airport consultants and researchers have developed their own analytical delay models for estimating average aircraft delay using estimates of hourly demand and hourly airfield capacity as the key inputs. Level 5 delay simulation models provide estimates of aircraft delay as their primary output. Aircraft delays also can be estimated using the AC by comparing annual demand in terms of aircraft operations to estimated ASV calculated using the formula discussed in this chapter. Average aircraft delay can then be estimated by using the ratio of annual demand to ASV along with a set of delay curves presented in the AC, wherein the horizontal axis of those delay curves is the ratio of annual demand to ASV, and the vertical axis is average annual aircraft delay in minutes per operation. Application of Airfield Service Volumes and Aircraft Delay Thresholds As described under the definitions of capacity provided in Chapter 1 of this guidebook, there has long been interest in specifying a definition of practical airfield capacity or airfield service volume, which can be generally defined as follows: Practical Airfield Capacity/Service Volume: The maximum number of aircraft operations that can be accommodated on an airfield at a specified level of service, 2FAA’s Pilot/Controller Glossary is an online document available at: http://www.faa.gov/air_traffic/publications/ atpubs/pcg/A.HTM. (Accessed August 22, 2012).

Subsequent Uses of airfield Capacity estimates 95 typically defined in terms of a threshold (or acceptable) level of average annual air- craft delay (e.g., 7 minutes per aircraft operation). According to FAA guidance, “traditionally, 4 to 6 minutes of average annual delay per aircraft operation is used in ASV calculation. This can be considered as an acceptable level of delay. When the average annual delay per aircraft operation reaches 4 to 6 minutes, the airport is approaching its practical capacity and is generally considered congested.”3 In a 1995 report to Congress, the U.S. Department of Transportation (DOT) states: “There are no defined criteria that delineate acceptable versus unacceptable delays.”4 Figure 6-4 illustrates the relationship between annual demand and average aircraft delay and the concept of express- ing service volumes as a function of threshold levels of delay (i.e., acceptable and unacceptable levels of average aircraft delay). In the absence of specific acceptability criteria for delays, the following scale for levels of service was suggested in the 1995 report to gauge the extent to which delays are tolerated rather than accepted: • 4 to 6 Minutes of Delay per Operation. Less efficient overall operations; limited peak-hour visual flight rules (VFR) delays along with instrument flight rules (IFR) delays experienced in both moderate and extreme weather conditions. 3FAA. AC 150/5070-6B, Airport Master Plans, May 2007. 4GRA, Inc. A Study of the High Density Rule, Technical Supplement Number Three, Analytical Concepts and Methods, prepared for the U.S. Department of Transportation, Federal Aviation Administration, May 1995. Source: LeighFisher. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Annual Aircraft Operations 20 10 (38 1,8 45 o ps ) No Action No Action with arrival use of Runway Rotated crosswind North parallel South parallel w/ restrictions South parallel without restrictions A ve ra ge a nn ua l a irc ra ft de la y (m inu tes pe r o pe ra tio n) UNACCEPTABLE MAXIMUM ACCEPTABLE DELAY RANGE South & North parallels without restrictions Figure 6-4. Typical aircraft delay curves for a set of airfield improvement alternatives showing ranges of acceptable versus unacceptable delays.

96 evaluating airfield Capacity • 6 to 8 Minutes of Delay per Operation. Increasing VFR delays in peak hours; increasing delays and eroding operational reliability in IFR conditions; high sensitivity to operational anomalies. • 8 to 10 Minutes of Delay per Operation. Increasing VFR delays in peak hours with transla- tion to shoulder hours in all but optimum conditions; high delay in IFR conditions with resulting flight cancellations. • Over 10 Minutes of Delay per Operation. VFR operations experience increasing delays in peak periods and shoulder hours in all but optimum conditions; very high delays in IFR conditions, resulting in extensive flight cancellations. Defining and Measuring Aircraft Delay and Airport Capacity Thresholds A detailed description of how aircraft delay is measured and identification of the thresh- olds of aircraft delay that would warrant capacity enhancements are outside the purview of this guidebook. However, ACRP Project 03-20, “Defining and Measuring Aircraft Delay and Airport Capacity Thresholds,” is a natural follow-on to ACRP Report 79 and will address these delay top- ics. The research findings developed under ACRP Project 03-20 are expected to (1) provide an inventory of and describe the different aircraft delay and airfield capacity metrics used within the industry, and (2) offer guidance about various delay and capacity metrics and when they should be used, particularly within the context of evaluating capacity enhancements. Research results of ACRP Project 03-20 are expected to be completed in 2012.