Air Tractor Inc AT 301 N8878S accident near Basin City, Washington

Probable cause

Maintenance personnel’s and the airplane owner’s failure to inspect the engine for cracks in the cylinders as required by an airworthiness directive, which resulted in the loss of engine power during low-altitude maneuvering flight.

NTSB analysis

The commercial pilot was conducting an agricultural application flight. The pilot reported that, when he was maneuvering the airplane about 30 to 50 ft above ground level , the engine experienced a total loss of power. The pilot conducted an emergency landing to a field, during which the airplane collided with an irrigation system.

The postaccident examination of the engine revealed that one of the cylinder heads had a crack in the dome between the forward and aft spark plug holes. The fracture surfaces were consistent with fatigue that had originated from multiple origins at the exterior of the cylinder head.

The Federal Aviation Administration had previously issued an airworthiness directive (AD) to address cylinder head cracking on the accident model engine. The AD required periodic visual inspections for cracks in the cylinder heads at specified intervals time in service (100 hours for the accident airplane) and fluorescent penetration inspections at cylinder overhaul. Further, the AD instructed maintenance personnel to focus the inspections on the area where the accident cylinder was cracked. According to the engine maintenance logbooks, the AD was last complied with about 225 hours before the accident, over twice the required interval. The last inspection before this inspection occurred about 180 hours previously, indicating that neither maintenance personnel nor the owner were regularly complying with the AD. According to the stamps on the cylinder, the last fluorescent penetration inspection was performed 10 years before the accident.

Text from the NTSB. Open the NTSB docket for WPR15LA023 for the full record.