N878AH

On November 21, 2020, about 1250 Pacific standard time, a Cessna TU206G, N878AH, was substantially damaged when it was involved in an accident in Twentynine Palms, California. The pilot and his five passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot reported that the accident flight was the first flight after the completion of the airplane’s annual inspection. He departed from South Valley Regional Airport (KU42), in Salt Lake City, Utah with the destination of Jacqueline Cochran Regional Airport (KTRM) in Thermal, California. The pilot recalled that about 275 nm into the flight, the engine began running rough, the No. 2-cylinder head temperature decreased from 1,350° F to 650° F, and the airplane’s airspeed decreased about 23 knots. The pilot decided to continue the remaining 200 nautical mile (nm) flight to his destination. However, about 168 nm later, the pilot once again noticed a “slight roughness” then it seemed to be “ok”. The pilot switched the fuel selector from the left tank to the right tank and the engine lost total power. He turned on the auxiliary fuel pump and the engine regained power. The pilot elected to land at the nearest available airport and have a mechanic look over the engine.

Twentynine Palms Airport was the nearest available airport, but there were no mechanics available to assist. The pilot refueled the airplane taking on 35 gallons of 100LL and taxied to runway 26 with the intent to fly the remaining 32 nm to his destination airport. He reported that he had completed an engine run-up, entered the runway and initiated the takeoff roll. About halfway into the takeoff roll, he felt a “slight hesitation” in engine power, and he aborted the takeoff. The pilot taxied back to runway 26 and completed another engine run-up during the takeoff roll, the engine power appeared to be normal; however, upon reaching about 250 ft agl, a total loss of engine power occurred, and the airplane descended. The pilot made a slight left turn during the descent to avoid colliding with a home and the airplane touched down on the sand covered desert terrain. The airplane impacted a sand berm and nosed over, sustaining substantial damage to the right wing and wing left strut.

Examination of the airplane’s fuel system revealed no anomalies or malfunctions. An external examination of the airplane’s engine and accessory case revealed no anomalies. The top spark plugs were removed from each cylinder and thumb compression could not be obtained on cylinders Nos. 2 and 5. A lighted borescope was used to examine each of the effected cylinders and revealed that the No. 2 cylinder exhaust valve was missing about 45 percent of the valve head. Foreign object compression signatures were sustained to the No. 2 piston and cylinder head. The missing exhaust valve head was not present in the No. 2 cylinder. Additionally, the No. 5 cylinder piston and cylinder head sustained foreign object compression signatures. The No. 5 cylinder top and bottom spark plugs sustained damage to the three ground electrode points, and the center electrode to the copper core. The No. 5 cylinder exhaust valve and intake valve were present and sustained foreign object compression signatures.

According to the airplane’s maintenance logbook, the engine total time was 2,180.1 hours when the annual inspection was completed. The engine had acquired 3 hours since the last annual. The engine was overhauled after acquiring 909 hours. At the time of the accident, the engine had amassed 1,274.1 hours since major overhaul.