Grumman G164 N6894Q accident near Juliaetta, Idaho

Probable cause

A partial loss of engine power due to a crack in the No. 2 cylinder.

NTSB analysis

The commercial pilot was conducting an agricultural application flight. The pilot reported that, while maneuvering the airplane about 300 ft above ground level, the engine experienced a partial loss of power. Unable to maintain altitude, the pilot conducted an emergency landing to a field, during which the airplane landed hard and nosed over, coming to rest inverted. Postaccident examination of the engine revealed that the No. 2 cylinder head exhibited a circumferential crack of its barrel between the cooling fins.

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 of time in service (every 100 hours for the accident airplane). According to the engine maintenance logbooks, the AD was last complied with about 35 hours before the accident. The previous inspections to this were sporadic, indicating that neither maintenance personnel nor the owner(s) were regularly complying with the AD.

Text from the NTSB. Open the NTSB docket for WPR16LA082 for the full record.