The Sonex had just departed the airport in Wellington, Fla. One witness reported that during the initial climb the engine “sputtered,” and another reported that it “backfired.”
The pilot made a steep turn back toward the airport, but the airplane stalled and spiraled to the ground. The pilot died in the crash.
The plane was equipped with an electronic flight instrument system that recorded numerous engine and flight parameters. Review of the downloaded data revealed that, initially, the engine was operating normally and within design parameters.
However, toward the end of the recorded data, the No. 1 cylinder head and exhaust gas temperatures had begun to decrease while the other cylinder temperature parameters remained fairly constant. The engine data then recorded a decrease in engine rpm followed by a steep 180° turn toward the airport.
A witness who assisted the pilot with the airplane’s oil change two days earlier stated that the pilot had cross-threaded a spark plug in the No. 1 cylinder and attempted a helicoil repair.
During the examination after the accident, the No. 1 spark plug was easily removed by hand. This was likely the cause of the power loss that preceded the pilot’s attempt to return to the airport.
The pilot’s steep, 180° turn exceeded the airplane’s critical angle of attack, which resulted in a stall at low altitude and collision with terrain.
The NTSB determined the probable cause as the pilot’s failure to maintain adequate airspeed following a partial loss of engine power during initial climb, which led to the airplane exceeding its critical angle of attack and experiencing an aerodynamic stall. Contributing to the accident was the pilot’s improper repair of a stripped spark plug hole, which led to a partial loss of engine power during initial climb.
NTSB Identification: ERA14FA123
This February 2014 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.