This April 2009 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Aircraft: Cessna 172. Injuries: 2 Minor. Location: Chesterfield, S.C. Aircraft damage: Substantial.
What reportedly happened: The pilot stated that while flying pipeline patrol about 500 feet above ground level, the engine began to run rough and lose power. He adjusted the carburetor heat, throttle, and mixture controls to the “full” positions, as well as adjusting the fuel selector to all positions, with no change in engine performance. He turned toward the nearest airport and noted that the engine RPM had decayed to 1900 as the airplane descended. The pilot determined that he could not reach the airport and made an emergency landing in trees.
Post-accident, the engine started and ran but did not develop full power. Disassembly of the engine revealed excessive wear and a broken exhaust valve. The engine manufacturer recommended overhaul at 2,000 engine hours, or 12 calendar years, whichever occurred first. Examination of aircraft logbooks revealed that the engine had accrued 2,403 hours and nearly 13 years since its last overhaul.
Probable cause: The partial loss of engine power due to a broken exhaust valve. Contributing to the accident was the operator’s exceeding the engine manufacturer’s recommended time before overhaul.
For more information: NTSB.gov
