Piper PA32R N9084J accident near Bethel, Alaska

Probable cause

A total loss of engine power due to oil starvation, which resulted from an oil cooler leak at a fractured brazed seam.

NTSB analysis

The commercial pilot reported that the airplane took off, and at 800 ft, the engine oil pressure dropped to zero. The pilot stated that he immediately turned back to the departure airport and that, while he was maneuvering for landing, the engine began "popping loudly," and engine oil began emanating from the oil access panel and splattered onto the windscreen. Shortly after, the engine lost all power. The pilot subsequently conducted a forced landing on tundra about 1 mile from the airport. During the landing roll, the nose and left landing gears collapsed, and the left wing and fuselage impacted terrain.

After the accident, a large puddle of oil was found on the airport ramp where the engine was started. During the recovery of the airplane, the engine oil access panel was found open with no dipstick present. The oil access panel had an impact mark on the underside that was about the same size as the dipstick top.

Postaccident examination of the engine revealed that there were holes and fractures on the top and bottom of the crankcase and that no oil was present in the oil tank. Several connecting rods were separated from the crankshaft and exhibited mechanical and thermal damage, consistent with oil starvation. When compressed air was applied to the right oil cooler, air was expelled from a small fracture between the brazed plates. Detailed examination of the oil cooler revealed an overstress fracture at a brazed seam; the fracture exhibited signatures of overstress with no evidence of preexisting defects. No anomalies of the oil pressure and temperature regulating systems were noted.

It is likely that the oil cooler seam fractured after the engine start and that most of the engine oil was expelled before takeoff. Once the oil supply to the engine was exhausted, the internal friction of the metal components resulted in thermal damage and connecting rod fractures and the subsequent loss of all engine power. It is possible that the crankcase was pressurized during the engine failure sequence, which resulted in the oil dipstick being ejected from the engine. The reason for the engine oil overpressure in the oil cooler could not be determined.

Text from the NTSB. Open the NTSB docket for ANC17LA006 for the full record.