Accident Details
A helicopter was purchased and flown approximately one hour to another airport. The following day, the pilot departed on a ferry flight. About five minutes after takeoff, the engine lost power when the rotor RPM dropped to 1,900, and the pilot initiated an autorotation. During the descent, the engine continued to idle, and the cabin filled with smoke. The helicopter touched down hard, and the main rotor blades struck the tailboom.
Maintenance History
The helicopter's last annual inspection occurred 53 months before the accident. A Special Flight Permit was issued by the Federal Aviation Administration (FAA) for the ferry flight. The engine had been overhauled 33 months before the accident. From the date of overhaul to the date of the helicopter's purchase, 3.9 hours had been logged on the engine. At the time of the accident, the engine had accumulated a total of 6.7 hours since overhaul.
Engine Examination
Examination of the engine revealed that the forward side of the #2 piston was melted and eroded away, and a hole had melted through the piston. An FAA publication described detonation as a form of spontaneous combustion that can burn a hole completely through a piston.