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95 10 APPENDIX D âDIFFERENCE BETWEEN ACCELERATE-STOP DISTANCE AND TAKEOFF DISTANCE TO CLEAR CRITICAL OBSTACLE FOR TWIN-ENGINE PISTON AIRCRAFT There are a total of eight twin-engine piston-powered aircraft in SARLAT. For twin-engine aircraft SARLAT reports accelerate-stop distance instead of takeoff distance to clear the critical obstacle because piston-engine aircraft are more prone to failure compared to turboprop and turbofan engine powered aircraft. During the project, we collected informal pilot operational procedures and found that all twin-engine piston aircraft pilots use the accelerate-stop distance in their calculations for runway distance. This appendix presents information on the differences between takeoff distance to clear the critical obstacle and accelerate-stop-distance for six twin-engine piston-powered aircraft. One exception of using accelerate-stop-distance in SARLAT for a twin- engine piston aircraft is the Diamond 42 Twin Star. Diamond only provides information on takeoff distance over 50 ft obstacle. That is the takeoff distance reported in SARLAT. Figure 51 shows the difference between accelerate-stop distance and takeoff distance to clear the critical obstacle for twin-engine piston aircraft at three different temperature conditions (ISA, ISA+31°F, and ISA+45°F). The y-axis of each plot shows the additional distance required if accelerate-stop-distance is used instead of takeoff distance to clear the critical obstacle. To illustrate the point, consider a Cessna 340 operating at sea level and ISA + 31 deg. F. conditions. For those conditions the accelerate-stop-distance is 1,170 feet longer than the takeoff distance to clear the critical obstacle. Figure 52 shows the takeoff distance to clear the critical obstacle for the same six twin-engine aircraft. For the same Cessna 340, Figure 52 shows a takeoff distance to clear the critical obstacle is 2,640 feet at sea level and ISA + 31 deg. Fahrenheit conditions. SARLAT reports 3,810 feet of takeoff distance needed for the Cessna 340 (using 90% useful load). The value of Figure 52 is that airport designers have takeoff distance to clear the critical obstacle for most twin-engine piston aircraft. Figure 52 does not present data for the Beechcraft Baron 55 because its takeoff performance is matched by the Beechcraft Baron 58. Figure 51 shows that the additional distance between accelerate-stop-distance for the Cessna 402B, Cessna 421, and Cessna 340 increase monotonically with airport elevation. All three larger Cessna twins have turbocharged engines. The trend for the non-turbocharged aircraft (Cessna 310, Beechcraft Baron 58, and the Piper Twin Comanche) is the opposite, a reduction in the difference between accelerate-stop- distance and takeoff distance as airport elevation increases. The performance degradation in climb for non-turbocharged engine aircraft produces longer takeoff distances to clear the critical obstacle.
96 Figure 51: Difference Between Accelerate-Stop Distance and Takeoff Distance to clear the Critical Obstacle.
97 Figure 52: Takeoff Distance to Clear Critical Obstacle for Twin-engine Piston-powered Aircraft in SARLAT
