Cessna 172S N5274Q accident near Wellston, Ohio

Probable cause

The failure of a connecting rod small end bushing, which resulted in a loss of engine power.

NTSB analysis

The commercial pilot and observer were conducting an aerial observation flight of a pipeline. The pilot reported that, while maneuvering at a low altitude toward an airport to refuel, he heard a "significant boom" and noticed a reduction in engine rpm. The pilot unsuccessfully attempted to regain engine power and then initiated a forced landing to a space between trees. During the forced landing, the airplane impacted rolling, uneven grass terrain and a barbed wire fence.

Examination and disassembly of the engine revealed a large hole on the top of the engine crankcase inboard of the No. 4 cylinder. The examination revealed that the No. 4 connecting rod had failed due to the installation of a nonconforming small end connecting rod bushing. Five days before the accident, the engine manufacturer had issued a mandatory service bulletin indicating that the accident connecting rod bushing may not have met engine specifications and may require followup action. Six days after the accident, the Federal Aviation Administration issued an airworthiness directive that required inspecting the connecting rods, replacing affected connecting rod small end bushings, and accomplishing the instructions in the engine manufacturer's mandatory service bulletin.

Text from the NTSB. Open the NTSB docket for CEN17LA311 for the full record.