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46 5 RUNWAY DESIGN CASE STUDIES The scenarios described in this section represent possible real-world applications of the Small Aircraft Runway Length Analysis Tool (SARLAT). These analyses are for runway length design and evaluation only, and they do not indicate the use of the tool for flight operations purposes. When performing SARLAT analysis using the runway design mode, the tool produces individual aircraft runway length requirements graphically. Six individual conditions break down these requirements: Takeoff on a dry runway, takeoff on a wet runway, landing on a dry runway, landing on a wet runway, landing under Part 135 regulations on a dry runway, and landing under Part 135 regulations on a wet runway. An in-depth discussion of FAA 14 CFR Part 135 Air Carrier and Operator Certification relating to runway length requirements are included under Case Study #5. When using the runway evaluation mode of SARLAT, the results are presented as a table containing several columns of information. Under takeoff weight, the table lists the maximum weight the aircraft can take off given the scenario conditions for both a dry and a wet runway. To the right of each weight is a color-coded percentage value. This value represents the percentage of the maximum takeoff weight allowed under scenario conditions compared to the aircraft's unconstrained maximum takeoff weight, as listed by the manufacturer. This value appears green if the percentage is from 75%-100% and orange if the value is less than 75%. A red x will appear in place of the percentage if the operation of the aircraft is not possible under the input conditions. Additionally, columns are provided for landing at the maximum landing weight. These columns contain either a green checkmark, indicating that the landing is possible, or a red x, indicating that a landing at maximum landing weight is not feasible. It is important to note that while a red x may be indicated, it is likely that landing is still possible for the aircraft at a less than maximum landing weight. 5.1 CASE STUDY #1: NEW AIRPORT A rural, mountainous community located in the southeastern United States plans to build a new airport on undeveloped land. The new airport will be equipped with a single, paved runway to serve the community. The anticipated aircraft fleet mix was developed for the new airport (Table 8). The critical aircraft for the 20-year planning period was identified as the Beechcraft 55 Baron. The critical aircraft is defined by the Federal Aviation Administration (FAA) in Advisory Circular 150/5000-17, Critical Aircraft and Regular Use Determination (2017) as the most demanding aircraft to make regular use of the airport. The FAA considers regular use to be at least 500 annual operations, including itinerant and local operations. No aircraft operating under Part 135 regulations are anticipated at this airport for the planning period. As a result, Part 135 operations are not selected in the analysis. In addition to the fleet mix, the planning team determined the scenario inputs for the runway design model (see Table 9). The proposed airport will be built at an elevation of 1,450 feet Mean Sea Level (MSL). The design temperature, the mean daily maximum temperature of the hottest month of the year, was determined to be 85oF in July. Wind conditions were assumed to be calm for the analysis. Preliminary engineering for the proposed runway has determined an anticipated runway gradient of 0.9%.
47 Table 8: Case Study #1 Fleet Mix. FAA Aircraft Identifier Aircraft Name Useful Load (%) Piston Piston BE55 Beechcraft 55 Baron 100 BE58 Beechcraft 58 Baron 100 C172 Cessna 172 Skyhawk 100 C182 Cessna 182 Skylane 100 SR22 Cirrus SR 22 100 DA40 Diamond 40 Star 100 M20P Mooney M20J 100 RV12 Vans RV 12 100 Turboprop Turboprop BE20 Beechcraft B200 King Air 90 BE9L Beechcraft C90 King Air 90 PC12 Pilatus PC 12 NG 90 PA46 Piper 46 Malibu Meridian 90 TBM7 Socata TBM 700 90 Turbofan Turbofan C56X Cessna 560 XL 90 C525 Cessna CitationJet1 90 Table 9: Case Study #1 Inputs. Scenario Inputs Values Pressure Altitude (Field Elevation) (ft) 1450 Air Temperature (F) 85o Wind Speed (knots) 0 Runway Gradient (%) 0.9 Surface Type Paved
48 Using the SARLAT, we perform a runway design analysis that produces runway length requirements for each aircraft, given the model inputs. The tool output depicts each aircraft graphically in the fleet mix and its corresponding runway length requirements (see Figure 32). In this case, the critical aircraft, the Beechcraft 55 Baron, is not the most demanding aircraft in the fleet mix. The Cessna 560 XL and Cessna Citation Jet1 require 4,577 feet and 4,704 feet for dry takeoff, respectively, whereas the Beechcraft 55 Baron requires 4,410 feet of runway. However, Cessna 560 XL and Cessna Citation Jet1 operations at the airport will not exceed 500 per year for the 20-year planning period. Therefore, the Beechcraft 55 Baron is the critical aircraft for runway length design. In this scenario, a design runway length of 4,500 feet is appropriate. This length is rounded up from 4,410 feet for constructability purposes. This length will adequately serve the fleet mix, including the critical aircraft, under dry takeoff conditions. Note that runway length requirements for takeoff on a wet runway are higher than takeoff on a dry runway. While this consideration for wet conditions would result in a longer runway length recommendation, ultimately, the design for this scenario is based on takeoff on a dry runway. FAA guidelines for runway design under AC 150/5325-4B Runway Length Requirements for Airport Design (2005) assume takeoff on dry runway surfaces when selecting an appropriate runway length.
49 Figure 32: Case Study #1 Runway Length Requirements. 5.2 CASE STUDY #2: CONSTRAINED RUNWAY An airport located high in the mountains of the American Southwest serves general aviation traffic for a small city community. Nearby housing developments and steep terrain have effectively prohibited the possibility of any extension to the existing runway. Given this reality, airport management would like to understand how aircraft currently operating at the airport are affected by the runway length. A fleet mix was identified based on actual operations data at the airport (see Table 10). The scenario inputs for the runway evaluation model were determined based on data for the existing runway (Table 11). The airport is located at an elevation of 7150 feet MSL, the design temperature is 80oF, and wind conditions were assumed to be calm for the analysis. The existing runway is 6000 feet long and has a gradient of 1.5%. Cessna 560 XL and Cessna Citation Jet1 require 4,577 feet and 4,704 feet for dry takeoff conditions, respectively, but they do not meet the 500 annual operations requirement to be the critical aircraft. The Beechcraft 55 Baron will dictate the runway length recommendation because it is the critical aircraft for planning purposes.
50 Table 10: Case Study #2 Fleet Mix. FAA Aircraft Identifier Aircraft Name Aircraft Mix (%) Piston Piston C172 Cessna 172 Skyhawk 3 C182 Cessna 182 Skylane 7 C340 Cessna 340 1 C421 Cessna 421 Golden Eagle 1 C206 Cessna T206 Turbo Stationair 1 C210 Cessna T210 Turbo Centurion 2 SR22 Cirrus SR 22 2 M20P Mooney M20J 10 M20T Mooney M20V Acclaim 1 PA28B Piper 28B Dakota 1 PA30 Piper 30 Twin Comanche 2 RV12 Vans RV 12 1 Turboprop Turboprop BE20 Beechcraft B200 King Air 4 BE9L Beechcraft C90 King Air 8 C208 Cessna 208 Caravan 10 PC12 Pilatus PC 12 NG 36 PA46 Piper 46 Malibu Meridian 1 TBM7 Socata TBM 700 1 Jet Jet C560X Cessna 560 XL 3 C525 Cessna CitationJet1 4 E55P Phenom 300 1
51 Table 11: Case Study #2 Inputs. Scenario Inputs Values Pressure Altitude (Field Elevation) (ft) 7150 Air Temperature (F) 80o Wind Speed (knots) 0 Runway Length (ft) 6000 Runway Gradient (%) 1.5 Surface Type Paved An analysis in SARLAT was performed using the existing runway characteristics. The results table (see Figure 33) contains several columns of information. This information reveals that while most piston and turboprop aircraft can operate without significant payload restrictions, jets are very limited in useful load under the existing conditions, including at the mean maximum daily temperature of the hottest month (July). Given that the runway cannot practically be extended due to existing conditions, it appears that jets operating at the airport are heavily restricted during the hot summer months. From an airport management perspective, these restrictions may result in a loss of fuel sales for the airport as these jets cannot carry as much weight in fuel. However, a broader array of operations can be performed under colder temperature conditions. For example, reducing the design temperature to 50oF results in an 80% useful load for the three jets included in the fleet mix (see Figure 34). This information is helpful for airport management to understand why jet traffic is sometimes restricted or not possible at the airport under certain meteorological conditions or at certain times of the year.
52 Figure 33: Case Study #2 Runway Evaluation.
53 Figure 34: Case Study #2 Runway Evaluation at Lower Temperature. 5.3 CASE STUDY #3: RUNWAY EXTENSION A small private airport is planning to extend its only runway to accommodate aircraft more effectively. The existing runway is a 3600-foot-long turf runway. Airport operations data was examined and utilized to develop the design fleet mix (Table 12). The Cessna 310 is the critical aircraft for the airport, and the existing runway length currently restricts Cessna 310 operations. Some Cessna 310 flights are either impossible or heavily restricted in useful load under adverse weather conditions, such as rainy or high-temperature days. No aircraft operating under Part 135 regulations were identified in the fleet mix. As a result, Part 135 was not included in the analysis. The scenario inputs for the analysis were determined based on data for the existing runway (see Table 13). The airport is located at an elevation of 1,200 feet MSL, the design temperature is 85oF for the hottest month of the year, and wind conditions were assumed to be calm for the analysis. The existing runway is 3,600 feet long and has a gradient of 0.2%. Due to a steep grade drop-off beyond the end of the existing runway, an extension is expected to be costly. The length of the extension needs to be carefully selected to accommodate the aircraft without incurring an excessive cost for the owner.
54 Table 12: Case Study #3 Fleet Mix. FAA Aircraft Identifier Aircraft Name Aircraft Mix (%) Useful Load (%) Piston Piston C172 Cessna 172 Skyhawk 15 100 C180 Cessna 180 Skywagon 11 100 C180 Cessna 182 Skylane 14 100 C206 Cessna T206 Turbo Stationair 19 100 C210 Cessna T210 Turbo Centurion 9 100 DA40 Diamond 40 Star 8 100 C310 Cessna 310 21 75 Turboprop Turboprop C208 Cessna 208 Caravan 2 90 TBM7 Socata TBM 700 1 90 Table 13: Case Study #3 Inputs. Scenario Inputs Values Pressure Altitude (Field Elevation) (ft) 1200 Air Temperature (F) 85o Wind Speed (knots) 0 Runway Length (ft) 3600 (Existing) Runway Gradient (%) 0.2 Surface Type Grass
55 An evaluation of the existing runway length (3,600 feet) in SARLAT reveals that the Cessna 310 is currently limited at 57% useful load (Figure 35). Airport management would like the aircraft to operate at the airport at a minimum of 75% useful load under scenario input conditions. A runway length design case was performed in SARLAT using the fleet mix for the airport at a useful load of 75% for the Cessna 310 (Figure 36). The results indicate a runway length of 4,338 feet is needed for the Cessna 310 to operate at the desired useful load. Based on these results, airport ownership has elected to extend the runway by 800 feet to achieve a total runway length of 4,400 feet. Using this new length in runway evaluation mode, the results confirm that the Cessna 310 can now operate just above the desired useful load at 76% (Figure 37). Figure 35: Case Study #3 Existing Runway.
56 Figure 36: Case Study #3 Runway Design. Figure 37: Case Study #3 Proposed Runway.
57 5.4 CASE STUDY #4: PERMANENT RUNWAY SHORTENING (DUE TO OBSTRUCTIONS) A small airport in the northeastern United States has identified several obstructions that FAA has determined to be hazards to air navigation. These obstructions are buildings and other structures located in the approach to one runway end. The airport owner and agencies have determined that removal of the obstacles is not feasible at present. As such, the airport has decided to permanently alter the location of the threshold, thus also shifting the runway approach surface. An obstruction analysis determined that a displacement of 400 feet would be required to mitigate the obstruction hazards. The displacement of the runway threshold will likely have an impact on aircraft that are landing on or departing from the displaced runway end. To evaluate the impacts of the runway threshold displacement on current aircraft landing operations at the airport, an analysis in SARLAT was performed. Airport operations data indicated an overwhelming majority of the aircraft utilizing the airport were small piston aircraft (Table 14). This aircraft type accounted for 97% of the fleet mix, while a small set of turboprop aircraft made up the remaining 3%. There are no jet operation at the airport. The scenario inputs for the analysis were determined based on existing airport data (Table 15). The elevation of the airfield is 256â MSL, the design temperature is 80oF, and wind conditions were assumed to be calm. Two separate runway evaluation analyses were performed in SARLAT: one using the existing runway length of 2,700 feet (Figure 38), and the other using the new reduced runway length of 2,300 feet (Figure 39). In both cases a runway gradient of 0.9% was used.
58 Table 14: Case Study #4 Fleet Mix. FAA Aircraft Identifier Aircraft Name Aircraft Mix (%) Piston Piston C172 Cessna 172 Skyhawk 13 C177 Cessna 177 Cardinal 5 C180 Cessna 180 Skywagon 6 C182 Cessna 182 Skylane 12 C206 Cessna 206 Stationair 25 SR20 Cirrus SR 20 9 SR22 Cirrus SR 22 6 DA40 Diamond 40 Star 2 M20P Mooney M20J 2 PA28B Piper 28B Dakota 17 Turboprop Turboprop PC12 Pilatus PC 12 NG 1 PA46 Piper 46 Malibu Meridian 1 TBM7 Socata TBM 700 1 Table 15: Case Study #4 Inputs. Scenario Inputs Values Pressure Altitude (Field Elevation) (ft) 256 Air Temperature (F) 80o Wind Speed (knots) 0 Runway Length (ft) 2700 (Existing) 2300 (Altered) Runway Gradient (%) 0.9 Surface Type Paved
59 When evaluating and comparing the results of the two analyses, the findings indicate that the reduction in runway length does have an impact on several of the aircraft operating at the airport. In addition to a general reduction in useful load for many of the aircraft evaluated, several are now unable to operate under certain environmental conditions. Two turboprops, the Pilatus PC-12 NG and the Piper 46 Malibu Meridian, and one piston, the Cirrus SR 20, are no longer able to takeoff under scenario input conditions with a wet runway. A number of aircraft are heavily constrained in useful load for takeoff on a dry runway as well. The reduction in runway length also resulted in additional restrictions to landing at maximum landing weight for several of the aircraft. The results of this analysis are for runway planning purposes and are generally conservative. While landing on the shortened runway under maximum landing weight may be prohibitive for several aircraft, it does not necessarily mean that they are unable to land at a lighter weight or under different weather conditions. Figure 38: Case Study #4 Existing Runway Evaluation.
60 Figure 39: Case Study #4 Altered Runway Evaluation. 5.5 CASE STUDY #5: TEMPORARY RUNWAY SHORTENING (DUE TO CONSTRUCTION) An airport in the mid-Atlantic region of the United States is preparing for an upcoming construction project. The project will include earthwork and safety area grading just beyond the threshold of one of the runway ends. In order to keep the primary runway operational during the construction project, the threshold will be temporarily relocated. The new temporary threshold location will allow for aircraft to operate on the runway while maintaining minimum standards for safety areas and clearance for airspace approach surfaces over-top of the construction area. Project engineers determined that to maintain 25 feet of clearance from the construction equipment to the airspace approach surface, the runway threshold must be temporarily relocated by approximately 1,500 feet. Given the temporary reduction in runway length, airport management has requested an analysis of the effects on aircraft that currently utilize the runway. In particular, airport management would like to know if the reduction in runway length a significant impact on the charter service (14 CFR Part 135 operations) has based at the airport. This charter service operates several business jets. The fleet mix for the runway evaluation was prepared based on the airportâs operations data and includes these business jets (see Table 16). The scenario inputs for the analysis were determined based on existing airport data (Table 16). The elevation of the airfield is 309â MSL, the design temperature is 87oF, and wind conditions are assumed to be calm. Two separate runway evaluation analyses were performed in SARLAT: one using the existing runway length of 5800 feet (Table 17), and the other using the temporarily reduced runway length of 4,300 feet (Figure 40). In both cases a runway gradient of 0.5% was used.
61 Table 16: Case Study #5 Fleet Mix. FAA Aircraft Identifier Aircraft Name Aircraft Mix (%) Piston Piston BE55 Beechcraft 55 Baron 1 BE58 Beechcraft 58 Baron 2 C172 Cessna 172 Skyhawk 12 C177 Cessna 177 Cardinal 2 C182 Cessna 182 Skylane 8 C310 Cessna 310 5 C206 Cessna T206 Turbo Stationair 9 C210 Cessna T210 Turbo Centurion 1 SR20 Cirrus SR 20 2 SR22 Cirrus SR 22 9 DA40 Diamond 40 Star 4 M20P Mooney M20J 3 PA28B Piper 28B Dakota 6 P06T Tecnam P2006T 6 Turboprop Turboprop BE20 Beechcraft B200 King Air 3 BE9L Beechcraft C90 King Air 3 B350 Beechcraft King Air 350ER 1 C208 Cessna 208 Caravan 1 PC12 Pilatus PC 12 NG 2 PA46 Piper 46 Malibu Meridian 1 TBM7 Socata TBM 700 4 Jet Jet C56X Cessna 560 XL 9 C525 Cessna CitationJet 1 1
62 C25B Cessna CitationJet 3 3 E55P Phenom 300 2 Table 17: Case Study #5 Inputs. Scenario Inputs Values Pressure Altitude (Field Elevation) (ft) 309 Air Temperature (F) 87o Wind Speed (knots) 0 Runway Length (ft) 5800 (Existing) 4300 (Relocated) Runway Gradient (%) 0.5 Surface Type Paved The results illustrate that most of the aircraft in the fleet mix are unaffected by the temporary reduction in runway length. However, it is important to note several exceptions. The Beechcraft King Air 350ER is significantly restricted in takeoff weight due to the change in runway length. The useful load drops from 100% to 46% under dry takeoff conditions. The new temporary runway length also has an impact on the required landing runway length for jet aircraft operating under FAA 14 CFR Part 135 Air Carrier and Operator Certification. FAA Part 135 provides guidance and regulations for charter operations. Part 135 operational rules typically require aircraft to be able to land within 60% of the available runway length (Part 135). Under certain circumstances this requirement may be 75% (Part 135 Eligible). The construction project will have a major impact on the existing charter service and the ability to utilize the airport for Part 135 operations while the runway is temporarily shortened because the jet aircraft are not able to meet the 60% requirement for landing. This is noted by the red (X) mark in the Part 135 landing column in Figure 41. To further illustrate the restriction on jets operating under Part 135, a runway design analysis was performed in SARLAT (Figure 42). Using only the jets from the fleet mix and the scenario inputs from the runway evaluation model, the results confirm the determination that Part 135 jet operations are impacted in a major way due to the reduced runway length. All four jets require well over 4,300 feet for landings under Part 135. The Phenom 300 requires the least at 4,708 feet, but still needs over 400 feet more runway than the temporarily reduced runway provides. These aircraft will still be able to operate at the airport with the reduced runway length under Part 91 (e.g., for ferry flight operations), but they will not be able to operate as revenue flights under FAA Part 135 regulations. As such, airport management has elected to expedite the construction timeline as much as possible in order to minimize the impact on the charter service.
63 Figure 40: Case Study #5 Existing Runway Evaluation.
64 Figure 41: Case Study #5 Relocated Runway Evaluation.
65 Figure 42: Case Study #5 Runway Length â Turbofan Aircraft Analysis.
