Piper PA-32R-300 N8892E accident near Adrian, Michigan

Probable cause

The airframe and powerplant mechanic's lack of experience in the overhaul of the engine model and the improper torque of the crankshaft gear bolt, which resulted in fatigue failure of the bolt and a total loss of engine power during an approach for landing.

NTSB analysis

The pilot was performing a flight with an inspection authorization (IA) rated mechanic, who had performed a recent annual inspection of the airplane. During approach to the airport, the engine lost total power. The airplane impacted a fence and terrain short of the runway and sustained substantial damage. Postaccident examination of the engine revealed that the crankshaft gear bolt fractured. Metallurgical examination of the bolt revealed features consistent with fatigue cracking that initiated at multiple sites near the bottom of a thread root. These smaller cracks coalesced and propagated inward through more than half the crack section of the bolt. The bolt began to cycle under reverse bending, which initiated fatigue cracking at multiple sites along the thread root on the opposite side.

The airframe and powerplant (A&P) mechanic who performed a recent overhaul of the engine stated that the engine was the first of the "big" Lycoming engines that he had overhauled. The A&P mechanic stated that he did not like using the Lycoming manuals because they were hard to follow. He mentioned several times that he had contacted Lycoming to request assistance, and they worked with him in providing the necessary documentation needed for the work he was doing. The A&P mechanic stated that he did not torque the crankshaft gear bolt to the engine manufacturer's specifications. The engine overhaul was signed off by the A&P mechanic, and he stated that the IA mechanic just removed and reinstalled the engine onto the airplane. Regulatory requirements state a certificated mechanic may not supervise the maintenance, preventive maintenance, or alteration of, or approve and return to service, any aircraft or appliance, or part thereof, for which he is rated unless he has satisfactorily performed the work concerned at an earlier date.

Text from the NTSB. Open the NTSB docket for CEN19LA066 for the full record.