Piper PA-28-235 N8580N accident near Spartanburg, South Carolina

Probable cause

A partial separation of the crankshaft gear/bolt, which resulted in a total loss of engine power.

NTSB analysis

The pilot reported that the preflight inspection, run-up, and takeoff were routine. During the initial climb, about 600 ft above ground level (agl), a boom was heard and the engine rpm dropped to zero. The pilot completed a forced landing on a city street. On final approach to the road, the airplane struck live powerlines; however, the landing was completed without further incident. After landing, the pilot exited the airplane and deployed a fire extinguisher toward smoke emanating from the engine and cowling area. The power line strike resulted in substantial damage to the rudder.

Examination of the engine revealed that the crankshaft gear partially separated from the crankshaft. The crankshaft gear bolt was partially backed out from its normal position and a few threads were stripped. The safety clip remained attached. The crankshaft alignment dowel pin had sheared. This condition prevented crankshaft continuity to the engine’s accessory drive gears and resulted in the total loss of engine power.

Metallurgical examination of the fractured crankshaft gear alignment dowel revealed a shear overstress fracture. The shaft of the crankshaft drive gear bolt was bent near the start of the threads, the last threads were flattened, and the end face of the bolt was smeared.

An airworthiness directive (AD), in addition to an engine manufacturer service bulletin, required inspection and replacement of any worn alignment dowel and crankshaft drive gear bolt; however, the maintenance procedure was only required to be completed during engine overhaul, after a propeller strike, or whenever the crankshaft gear was removed. Although there were multiple maintenance logbook entries in the several years preceding the accident noting compliance with the propeller strike AD, there was no record that the AD/service bulletin (SB) was complied with in full (to include an inspection of the crankshaft drive gear, bolt, dowel pin, and replacement as warranted). There was also no record of a propeller strike.

The left magneto’s exterior casing was found fractured and partially rotated from its normal attachment points. Further disassembly of the unit found that its bearings rotated freely. In addition, the fracture surface of the left magneto gear tooth and the fracture surfaces of the left idler gear had features consistent with overstress separation. There was no evidence of recent maintenance to either magneto. It is likely that the left magneto damage and left idler gear damage was not an originating event that contributed to the loss of engine power based upon these factors.

The engine displayed sooting and thermal damage. The propeller blade tip exhibited black marks on the front side and a small section of the tip showed evidence of melting and erosion. The damage was consistent with electrical arcing damage as a result of striking powerlines during the emergency landing, which likely caused a fire in the engine compartment during the landing or landing roll, which was extinguished by the pilot with a fire extinguisher after exiting the airplane.

Text from the NTSB. Open the NTSB docket for ERA23LA037 for the full record.