Piper PA-22-150 N7640D accident near Anchorage, Alaska

Probable cause

A loss of engine power due to oil starvation as the result of a loose B-nut fitting on the engine oil cooler, resulting in a forced landing to a soft, snow-covered surface, and a subsequent nose over.

NTSB analysis

The pilot reported that while in level cruise flight he noticed the smell of burning oil, which was immediately followed by a change in engine sound, followed by a partial loss of engine power. The engine continued to lose power and the pilot selected a snow-covered beach as a forced landing site. During touchdown, as the airplane's main landing gear wheels contacted an area of deep snow, it abruptly nosed over, sustaining substantial damage to the wings, fuselage, and empennage.

Examination of the engine revealed that there was no engine oil in the sump. An oil cooler B-nut, which was located on the right side of the oil cooler, was found loose, and there was a significant oil streaking on the right side of the fuselage. Review of maintenance records revealed that there had been no recent maintenance activity to the oil cooler or other engine components adjacent to the loose B-nut. Given the accident pilot’s account of the accident, along with the discovery of the loose oil cooler B-nut, it is likely that the engine failed due to oil starvation after all engine oil was lost through the loose B-nut.

Text from the NTSB. Open the NTSB docket for ANC19LA011 for the full record.