On July 24, 2017, about 1156 Pacific daylight time, an experimental British Aircraft Corp STKMSTR MK80, N605GV, was destroyed when it involved in an accident near Henderson, Nevada. The pilot sustained minor injuries. The airplane was operated as a Public Use aircraft in support of the U.S. Air Force, on a cross-country flight.
According the pilot, shortly after takeoff, the airplane failed to accelerate, and he was unable to initiate a normal climb. The airplane subsequently struck terrain and was consumed by fire.
The two maintenance personnel who launched the airplane were also witnesses to the accident. One maintenance person stated that shortly after takeoff, “the airplane did not look like it was accelerating.” He further stated, “he saw the left-wing dip and the airplane pancaked down.” The other maintenance person stated that “he saw the airplane clear the airport fence and then settle towards the ground.” He also stated that the airplane’s “engine sounded normal.”
The flight was delayed by maintenance due to the replacement of a flap control hydraulic valve assembly. The replacement actuator came from another same airplane of the same type. The replacement process consisted of changing five hydraulic lines and a “couple” of bolts; it took about 45 minutes to accomplish. Afterwards, the accident pilot was asked by maintenance to perform an engine run to check for the appropriate flap operation and potential leaks. Maintenance personnel had the pilot select the flaps to the UP position, half down position, and the fully extended position for about seven cycles.
Once the flap actuator replacement and associated operational checks were completed, the airplane was refueled for the flight. At this time, the flaps were observed noted to be in the Full Up position by one of the maintenance personnel. After engine start, the pilot ran operational checks on the flight controls, flaps, and speed brakes. Two maintenance personnel were present for the launch and stated that the flaps were fully extended when the airplane taxied out. They mentioned that the pilot would set the flaps for takeoff prior to takeoff, at the end of the runway.
The airplane checklist called to test/set the flaps on the After-Start checklist and to set the flaps for takeoff on the Before Take-off checklist. According to the aircraft flight manual, the position of the flaps was shown on a flap indicator on the left panel. The flap lever on the left side was in a quadrant, and gated at the takeoff position; it was necessary to pull the lever aft to pass down through the gate, or to push it forward to pass up through the gate. Selection of the take-off gate provided 30° of flaps and landing provided 50° of flaps.
Examination of the accident site by Federal Aviation Administration inspectors revealed that the airplane came to rest upright about 1/4 mile south of the departure end of runway 17R. All major components of the airplane necessary for flight were located in the wreckage.
Postaccident examination of the engine revealed no anomalies and an examination of the airframe revealed flight control continuity. The flaps were observed in the fully extended position. The flap hydraulic actuator was found seized in the flap fully extended position. When the right flap was actuated by hand, red fluid was observed leaking from a hydraulic line that had been cut during recovery. Furthermore, the soot pattern on the leading edge of the flaps caused from the post impact fire, were consistent with the flaps being fully deployed. With the flaps retracted a different pattern of soot on the flap’s leading edge would have been displayed.
The accident pilot gave an updated statement several months after the accident. According to the FAA, he stated “. . . that is was possible the technique used to set the flaps for takeoff could have allowed them to drift down into the full position.”