Beech A36 N9410Q accident near Heavner, Oklahoma

Probable cause

A total loss of engine power due to oil exhaustion which resulted from improper engine maintenance.

NTSB analysis

The pilot reported that he noticed the engine oil pressure dropped to 14 psi after he began the descent to his destination airport. He turned toward a nearby airport, but shortly thereafter the oil pressure dropped to 0 psi and the engine seized. The pilot executed a forced landing to a field and the airplane sustained substantial damage to its wings when it struck fences and livestock feeding troughs during the landing.

Postaccident examination of the airplane revealed several missing and loose bolts securing the engine valve covers. The No. 4 cylinder valve cover was completely off and its gasket was not located after the accident. The No. 6 cylinder valve cover was very loose and was only held on by 4 of the 8 bolts normally used to secure the cover. The No. 4 cylinder valve arm shaft bolt was missing. Metal shavings were observed throughout the valve assembly area as well as deposited on the cowling and airplane along with the lost engine oil.

Review of maintenance records did not reveal any recorded maintenance to the rocker covers since the most recent engine overhaul 6 years before the accident. Maintenance entries since the overhaul indicated routine maintenance, including annual/100-hour inspections and oil changes, with no leaks detected during post-maintenance engine runs. Attempts to discover when the rocker covers were last accessed for maintenance were unsuccessful.

Based on the available evidence the loss of engine power was due to oil exhaustion that resulted from improper installation of the engine valve covers. Determination of when the improper maintenance was performed could not be determined based on the maintenance entries that were available.

Text from the NTSB. Open the NTSB docket for CEN22LA140 for the full record.