Accident Overview
On November 21, 2020, about 1250 Pacific standard time, a Cessna TU206G, registration N878AH, sustained substantial damage during an accident in Twentynine Palms, California. The pilot and five passengers were uninjured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Flight History
The accident flight was the first after the airplane's annual inspection. Departing from South Valley Regional Airport (KU42) in Salt Lake City, Utah, the pilot intended to land at Jacqueline Cochran Regional Airport (KTRM) in Thermal, California. Approximately 275 nautical miles into the flight, the engine began running rough, the No. 2 cylinder head temperature dropped from 1,350°F to 650°F, and airspeed decreased by about 23 knots. The pilot continued the remaining 200 nautical miles. About 168 nautical miles later, he noticed a slight roughness, which then seemed to subside. Switching the fuel selector from the left to the right tank resulted in a total loss of engine power, but turning on the auxiliary fuel pump restored power. The pilot diverted to the nearest airport, Twentynine Palms Airport, where no mechanics were available. After refueling with 35 gallons of 100LL, he taxied to runway 26.
During the takeoff roll, a slight hesitation in engine power prompted the pilot to abort. After taxiing back and performing another engine run-up, the takeoff appeared normal. However, upon reaching about 250 feet above ground level, a total loss of engine power occurred. The pilot made a slight left turn to avoid a home, touched down on sand-covered desert terrain, impacted a sand berm, and nosed over. The right wing and left wing strut were substantially damaged.
Engine and Fuel Examination
Examination of the fuel system revealed no anomalies. An external inspection of the engine and accessory case also showed no anomalies. The top spark plugs were removed from each cylinder; thumb compression could not be obtained on cylinders No. 2 and No. 5. A borescope examination of those cylinders revealed that the No. 2 cylinder exhaust valve was missing about 45 percent of its head. Foreign object compression signatures were found on the No. 2 piston and cylinder head; the missing valve head was not located in the cylinder. The No. 5 cylinder piston and cylinder head also had foreign object compression signatures. The No. 5 cylinder spark plugs sustained damage to the three ground electrode points and the center electrode to the copper core. The No. 5 cylinder exhaust and intake valves were present but exhibited foreign object compression signatures.
Maintenance Background
According to the airplane's maintenance logbook, the engine had accumulated 2,180.1 hours at the time of the annual inspection, with 3 hours since that inspection. The engine was overhauled after 909 hours and had amassed 1,274.1 hours since major overhaul at the time of the accident.