What happened
During a Part 135 on-demand air taxi flight, the number 3 cylinder and piston became physically separated, triggering an in-flight fire. Following the fire, the aircraft performed a crash landing on terrain located near the shoreline of a body of water. Of the four occupants on board, there were 3 fatalities and 1 survivor. The surviving passenger was unable to recall the specific events that led to the accident.
The investigation
Investigators examined the engine and reviewed maintenance history. Records showed that the number 3 and number 4 cylinder assemblies had been installed approximately 220 flight hours prior to the accident. This maintenance work had been completed without removing the engine from the aircraft, and no issues with the airframe or engine were reported following the cylinder change.
An inspection of the engine identified fatigue cracks in the case located beneath the number 3 cylinder. Under magnified inspection, the engine case showed evidence of wear and deformation damage where the cylinder's holding flange and inner skirt would normally be positioned. This damage was consistent with the cylinder moving in relation to the engine case. Additionally, mechanical damage was found on the threads of the studs and both through-bolts.