WPR12FA059 · Vans RV7 - A Donahoe

The pilot, who was also the owner and builder, was flying his experimental amateur-built airplane powered by a converted automobile engine back to his home airport after a brief personal out-and-back flight. Light winds and daylight visual meteorological conditions prevailed. Radar and GPS data showed that the return portion of the flight followed an essentially straight track in the direction of the pilot's home airport at an altitude of about 1,500 feet above ground level with a groundspeed of about 100 knots. When the airplane was about 12 miles from the airport, the groundspeed decreased to about 60 knots over a period of about 25 seconds. The airplane then entered a descent of about 800 feet per minute, which it maintained for the next minute. Shortly after the start of that descent, the transponder was switched to the emergency code of 7700. About 25 seconds later, the pilot transmitted a "mayday" call to the approach controller. He stated that he had a problem, and several seconds later, transmitted that he was "going down." In the radio call, the pilot named the component that he thought was causing the problem, but the transmission quality prevented a positive determination of exactly what the pilot said. The descent rate then increased rapidly, and the airplane impacted terrain several seconds later.

The damage to the rudder stop, rudder, elevator trim tab link, and elevator trim tab was inconclusive as to whether it occurred in flight or on impact. Propeller damage indicated that the propeller was not rotating or was rotating with little engine power. However, no preimpact mechanical problems with the engine, propeller gearbox, or propeller were identified.

The reconstructed flight path was consistent with a significant deceleration at a near-constant altitude, followed by a descent to maintain flying speed, followed by a loss of control and/or aerodynamic stall at low altitude, from which the airplane did not recover. The airplane had slowed and started to descend when the pilot took the deliberate actions of squawking 7700 and transmitting a radio distress call. He attempted to describe the problem that he perceived. During that time, the data suggests that the airplane was still controllable and was under control. Shortly thereafter, as evidenced by the significantly increased descent rate and the pilot's transmission that he was going down, control was lost, and the airplane impacted the ground.

The limited propeller damage, coupled with the engine's dependence on electricity and its electronics for continued operation, suggest that the deceleration could have been a result of an engine power loss for electrical or electronic reasons that could not be determined during postaccident examination. The specific reason for the stall could not be determined; however, the pilot may have been distracted by the emergency or the radio calls. The investigation was unable to determine the accuracy of the airspeed indicator or stall speed values. Further, the airplane does have a limited natural stall warning and no stall warning system to alert the pilot to an impending stall, particularly if he was distracted.

Verbatim NTSB analysis and probable cause from the NTSB dataset