What happened
During a cruise phase of flight, the pilot of an aircraft powered by two experimental Engine AIR Power Systems TSIVD-427 engines experienced significant power fluctuations. The pilot reported that one engine was surging and subsequently declared an emergency. While being vectored toward the airport, the aircraft struck a field adjacent to the runway, resulting in a post-impact fire.
The aircraft, which had accumulated between 8 and 10 total flight hours, had recently completed several long-distance flights, including a trip from Melbourne, Florida, to Canada. Prior to the accident, the right engine had demonstrated intermittent issues involving a loss of boost followed by overboosting, which could not be resolved through attempted repairs.
Findings
Investigation of the wreckage showed that both the engines and various accessories sustained heavy damage from the impact and the subsequent fire. While the right engine's crankshaft, valves, rods, and pistons remained continuous upon manual rotation of the propeller reduction control unit, the aircraft was operating under FAA limitations that restricted it to flight testing only. These limitations were intended to cover the first 100 hours of operation following the installation of the modified engines. Notably, there was no available data regarding the aircraft's performance capabilities during single-engine operations.