If you’ve been buzzing around the flatlands ’til now in piston airplanes, you’ve probably reduced the whole issue of performance to just a couple of items: cruise speed and fuel planning. While everyone studies takeoff and landing performance, a close look is rarely required for low-elevation piston operations. Those of us who routinely fly in mountainous areas, or who operate at gross weight in piston twins, must more frequently consider takeoff, climb, engine-out, and landing performances. In turbine-powered aircraft, these performance issues must be addressed more diligently than ever. Despite much greater installed power, most turbine aircraft tend to operate, in many respects, much closer to their limits than typical light piston aircraft. Runway length requirements, especially for jets, are much greater than for piston aircraft. Therefore, turbine aircraft tend to require a larger percentage of the average runway for operations. This calls for more careful planning, especially for the possibilities of engine failures, go-arounds, and aborted takeoffs. Also, turbine aircraft are designed to operate routinely at high weights since their best economic performance is generally tied to full passenger or freight loads. Even with all that extra power, many turbine aircraft don’t actually perform all that much better engine-out, at gross weight and high-density altitude, than many light piston twins. A related factor is the large range of weights at which a typical turbine aircraft operates. As you know, the operating airspeeds of an aircraft vary, based upon weight. Therefore, when flying at gross weight in a light aircraft, you may decide to rotate at a higher airspeed and on final to “cross the fence” a little faster than normal. Due to the range of operating weights for larger turbine aircraft, along with density altitude and other considerations, the spreads of proper rotation, emergency, and landing speeds
CHAPTER 10
Performance
are much larger. “A little faster” simply is not accurate enough for safe operation of turbine aircraft. Sure, cruise performance must be addressed on every flight, due to fuel planning requirements, but among the major performance planning issues for turbine aircraft are takeoff, climb, landing, and engine-out situations.
Takeoff, Climb, Landing, and Engine-Out Performance If you’ve been flying light piston aircraft until now, you’re used to learning a specific set of airspeeds for each plane. There was a standard takeoff rotation speed, best angle (VX ) and best rate of climb (VY) speeds, and recommended airspeeds for approach and for crossing the threshold on landing. These same parameters apply to turbine pilots, but they’re described differently. Since turbine aircraft operate under broad variations of weight, configuration, and environment, a wide range of operating speeds must be calculated for takeoff, landing, and emergency or abnormal operations (such as engine-out and noflap landings). Since pilots can’t possibly memorize every speed variation for every possible situation, an entire airspeed terminology has been developed that is unique to turbine aircraft. There’s more than convenience involved in the use of turbine “V-speeds.” Sharp multiengine piston pilots know the safety benefits of engine-out planning prior to takeoff. In the event of an aborted takeoff, will there be adequate runway for stopping? Can the trees be cleared in the event of an engine failure after rotation? The FAA has carefully defined calculation of turbine V-speeds in order to ensure that engine-out aircraft performance meets minimum safety standards 135
