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Aviation Accident

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NTSB Identification: ERA14FA123
14 CFR Part 91: General Aviation
Accident occurred Monday, February 17, 2014 in Wellington, FL
Probable Cause Approval Date: 12/09/2015
Aircraft: WILLIAMS CHRISTOPHER T SONEX, registration: N732SX
Injuries: 1 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The airplane had just departed the airport; one witness reported that during the initial climb the engine “sputtered,” and another reported that it “backfired.” The pilot then made a steep turn back toward the airport, but the airplane stalled and spiraled to the ground. The airplane 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-degree turn toward the airport. A witness who assisted the pilot with the airplane’s oil change 2 days earlier stated that the pilot had cross-threaded a spark plug in the No. 1 cylinder and attempted a helicoil repair. During examination after the accident, the No. 1 sparkplug 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-degree turn exceeded the airplane’s critical angle of attack, which resulted in a stall at low altitude and collision with terrain. A review of the pilot’s toxicology revealed that even though he tested positive for antidepressants, they were not a factor in the accident.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
  • 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.