Tuesday, November 6, 2012
Fundamental failures by pilots still figure in some accidents
According to documentation for the airplane, the minimum approach speed with both engines operating at gross weight of 6,200 pounds is 95 KIAS. For a normal landing at a weight of 4,300 pounds, the airplane should be at 79 KIAS when passing over a 50-foot obstacle prior to the runway. However, with one engine out, the minimum control speed is 82 KIAS.
According to the FAA's Airplane Flying Handbook: "If an engine fails below Vmc while airborne...the final approach should be made with power and at a speed recommended by the manufacturer, but in no case less than critical engine-out minimum control speed (Vmc)."
The NTSB determined that the probable cause of this accident was that the pilot didn't maintain minimum controllable airspeed while on final approach with a partial loss of power in the right engine, which resulted in a loss of control. Contributing to the accident was the partial loss of engine power in the right engine due to the improperly installed O-rings in the engine's throttle and control assembly.
A Piper PA-24 Comanche crashed about 450 yards north of the approach end of runway 30 at the Ernest A. Love Field, Prescott, Ariz. The pilot and passenger were fatally injured. A post-impact fire broke out. The planned destination was unknown.
Witnesses located at various points on the airport told investigators that during its initial climb, the airplane didn't appear to be more than 150 or 200 feet above the ground. The witness reports agreed that the airplane was "slow," was flying at a high angle of attack, and at times porpoising in the air. When the airplane had reached a point above the intersection of runways 21L and 30, it was in a shallow left bank that continued to increase before impacting the ground and bursting into flames. The witnesses also reported that the landing gear had been retracted prior to the airplane initiating the left bank. Two witnesses reported hearing a strong engine sound while on the takeoff initial climb; however, they also reported that at some point they weren't able to hear the engine.
The weather observation at the time of the accident included wind from 200 degrees at 9 knots gusting to 19 knots, temperature 32 degrees C., dew point -08 degrees C. and a calculated density altitude of 7,896 feet.
According to the FAA, the flight had been cleared for a full-length takeoff on runway 21L. Tower control personnel reported that at the intersection of runways 21L and 30, the pilot stated, "Comanche zero four Papa has to come back." The controller cleared the pilot to land on runway 30. There were no further transmissions from the pilot. Runway 21L was 7,626 feet long and 150 feet wide. The field elevation is 5,045 feet.
The private pilot had logged a total of 750 flight hours.
The NTSB determined that the probable cause of this accident was the pilot's failure to maintain an adequate airspeed while maneuvering to return to the runway at a high-density altitude, which resulted in an aerodynamic stall.
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