Primary finding
Probable cause
A total loss of engine power due to the failure of the No. 2 cylinder exhaust valve for reasons that could not be determined.
Investigator assessment
Analysis narrative
While in cruise flight, the airplane’s engine began to run rough. As the pilot was attempting to restore engine power, the engine experienced a total loss of engine power. The pilot performed a forced landing to a field and the airplane collided with terrain. A postaccident examination of the engine revealed that the No. 2 cylinder exhaust valve had failed, damaging the piston head and resulting in a loss of engine power. Machining of the fracture surfaces precluded determining the mode of failure. The engine was last overhauled about 32 years before the accident with just over 1,030 hours logged on the components. The engine manufacturer recommends an overhaul every 1,800 hours or 12 years.
Source record
Factual narrative
On August 15, 2021, about 1700 central daylight time, a Cessna 150H airplane, N50055, was substantially damaged when it was involved in an accident near Heavener, Oklahoma. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that while in cruise flight to his destination, the airplane’s engine began to run rough. As he attempted to troubleshoot the rough running engine, the engine stopped producing power. The pilot performed a forced landing to a field. During the landing, the airplane collided with a dirt mound and trees. Substantial damage was sustained to the fuselage and wings. A postaccident examination of the engine revealed the No. 2 cylinder exhaust valve was fractured with associated damage on the cylinder piston. Machining of the valve surfaces precluded analyzing the mode of failure. A review of maintenance logbooks revealed that the engine was last overhauled on October 17, 1988, at a tachometer time of 2,438 hours. A logbook entry recorded the work conducted to include replacement of the exhaust valves. The most recent inspection was a 100-hour type conducted on April 1, 2021, with a tachometer time of 3,469.17 hours. Continental Motors Service Information Letter SIL-98-9C, revised July 17, 2017, provides time limits between major overhauls on their engines. For the accident engine’s serial number range, overhauls should take place every 1,800 hours or 12 years.