Piper PA 28-161 N8440N accident near New Orleans, Louisiana

Probable cause

The in-flight fatigue failure of the crankshaft gear retaining bolt, which resulted in a total loss of engine power. Contributing to the accident were the pilot/owner’s failure to maintain the airplane in accordance with an airworthiness directive following a propeller strike and the improper installation of the lockplate.

NTSB analysis

The pilot/owner reported that, while on final approach to the destination airport, the engine experienced a total loss of power. The pilot was unable to restart the engine, and the airplane was unable to glide to the runway, so the pilot subsequently ditched the airplane into a lake. The pilot evacuated the airplane and swam to shore; the airplane sank into the lake but was subsequently recovered.

A postaccident examination of the engine's crankshaft gear, retaining bolt, and lockplate revealed that the retaining bolt had fractured; the fracture surfaces and the fine ratchet marks in the initiation area were consistent with fatigue crack propagation. Defined fretting wear scars were noted partially around the circumference of the bolt through-hole. The lockplate exhibited areas of fretting wear and polishing wear scars. The lockplate's retention tab was in the "open" position and did not exhibit typical mechanical deformation associated with bending to the "closed" position, which indicates that the lockplate was not installed properly.

The engine manufacturer had issued a service bulletin (SB) that outlined additional maintenance actions that should be taken if an engine experienced a propeller strike. Subsequently, the Federal Aviation Administration issued an airworthiness directive (AD) that made compliance with the SB mandatory. During the course of the investigation, the pilot reported that the engine had experienced a propeller strike days before the accident flight. He stated that he was unaware of the AD, so it was not accomplished after the propeller strike. It is likely that the crankshaft gear retaining bolt tension was loosened when the propeller strike occurred and that the improperly installed lockplate allowed the bolt to lose its clamping force. The loose bolt became fatigued and subsequently failed during the accident flight.

Text from the NTSB. Open the NTSB docket for CEN14LA449 for the full record.