Cessna R172 N180CM accident near College Station, Texas

Probable cause

The total loss of engine power due to the fatigue failure of the No. 1 connecting rod. Contributing to the accident was the manufacturer’s exclusion of the accident engine (by serial number) in a revision of a service bulletin.

NTSB analysis

The airline transport pilot was conducting a personal cross-country flight. The pilot reported that, during cruise flight, he heard a loud "pop or bang" and that the airplane started vibrating. The engine subsequently lost power. During the forced landing to a road, the airplane struck a building and then a truck.

An examination of the engine found two holes in the crankcase. Further examination revealed that the No. 1 connecting rod had failed due to fatigue. The engine manufacturer had previously issued a service bulletin (SB), which recommended the examination and potential replacement of the connecting rods in the accident engine due to wear or fatigue; the SB included both the accident engine's serial number and the connecting rod's forging stamp identification.

The engine manufacturer subsequently revised the SB; the revision excluded the accident engine by serial number but the connecting rods were still included. However, it would not be possible for a mechanic to identify the connecting rod serial numbers without taking the engine apart. A review of the maintenance records revealed that the accident engine was last overhauled about 5 years after the issuance of the revised SB; no entry was found indicating that the connecting rods were examined in accordance with the SB, and no subsequent maintenance occurred that would have allowed for the examination of the connecting rods. However, because this was a Part 91 operation, such an inspection was not mandatory. Despite the fact that the SB was not mandatory, because the manufacturer removed the engine serial number from the revised SB, a mechanic would have very little way of knowing whether the connecting rods should be inspected.

Text from the NTSB. Open the NTSB docket for CEN15LA416 for the full record.