Piper PA-25-235 N7279Z accident near Omega, Oklahoma

Probable cause

Improper base metal preparation or contamination of the No. 5 cylinder wall before it was coated, which resulted in the coating peeling off of the cylinder wall and contaminating the engine oil and the subsequent partial loss of engine power.

NTSB analysis

The commercial pilot was conducting an agricultural application flight. During the flight, the airplane was unable to maintain altitude, and the pilot conducted an emergency landing on a dirt road. During the landing roll, the left wing struck a fence, crushing the leading edge. The pilot reported that the oil temperature was extremely high and that the engine was having a problem producing power.

A postaccident engine examination revealed metal particles in the engine oil, oil pump, and oil sump. The oil was black and smelled burnt. Coating was peeling off of the No. 5 cylinder wall. Energy dispersive spectroscopy analysis of the cylinder base metal produced a spectrum consistent with a steel alloy; the spectrum of the coating was consistent with a nickel-silicon carbide. It is likely that the coating was peeling either due to improper base metal preparation or contamination of the cylinder wall before it was coated, which resulted in poor bond strength between the coating and inner wall of the barrel. The metal particles from the peeled coating contaminated the engine oil and resulted in the partial loss of power.

Text from the NTSB. Open the NTSB docket for CEN15LA238 for the full record.