Aero Commander 685 N74CP accident near Victoria, Texas

Probable cause

Maintenance personnel's failure to secure the left engine idler pin during overhaul, which resulted in a catastrophic engine failure and subsequent forced landing.

NTSB analysis

Two days before the accident, both engines lost power after takeoff. The pilot returned to the airport and landed the airplane uneventfully. Maintenance personnel were unable to determine the cause of the engines' power loss. Both engine wastegates were removed and bench tested, and they operated normally. Ground, high-speed taxi, and flight tests were conducted with no discrepancies noted. Earlier on the day of the accident, the airplane had been flown for an uneventful 45-minute flight. However, during takeoff for the accident flight, both engines lost power, and the pilot made a forced landing in a field. Disassembly of the left engine revealed that the idler pin was unsecured and that no nuts were present on either of the two bolt studs. The bolt studs were worn and stripped of threads near the base, consistent with being worn by the free movement of the idler pin. The engine casting where the idler pin was installed was fractured. The crankshaft, camshaft, starter drive, and starter adapter gear teeth were stripped, and metal fragments were noted in the oil screen and sump. The right engine was functionally tested and operated satisfactorily at all power settings. Based on the evidence found during the left engine examinations, it is likely that a catastrophic left engine failure occurred during the accident flight due to an unsecured idler pin.

Text from the NTSB. Open the NTSB docket for CEN13FA352 for the full record.