Ayres S2R N766BF accident near Breckenridge, Michigan

Probable cause

A total loss of engine power due to a lack of oil in the engine. The source of the inflight oil leak could not be determined based on the available information.

NTSB analysis

The pilot was departing on an agricultural application flight when after takeoff, about 100 ft above the ground, he observed a sudden increase in exhaust gas temperature (EGT) above the engine’s limitations. The pilot immediately reduced the throttle, but the engine had a total loss of engine power and the pilot made an immediate forced landing in a cornfield. The airplane fuselage and wings were substantially damaged during the forced landing.

Data downloaded from the airplane’s engine monitor confirmed there was a sudden and total loss of engine oil pressure that resulted in a loss of control of the propeller blade angle with a corresponding decrease in engine speed and increase of EGT. The decrease in oil pressure was consistent with a low oil supply to the main oil pump.

It was reported that engine oil was present in the oil tank, but the oil level was not verified at the accident site. However, a few weeks after the accident, the engine oil tank did not contain any oil when the engine was prepared for shipment. The oil tank was intact and was not breached. Additionally, the oil transfer hoses and fittings associated with the oil cooler were found intact and tight.

Postaccident disassembly of the engine did not reveal any evidence of a mechanical malfunction or failure that would have precluded normal operation. Normal oil wetting and wear signatures were observed throughout the engine. The investigation determined that the loss of engine oil was not from the engine.

The airframe portion of the engine oil system, consisting of the oil cooler and two transfer flex-hoses, was examined to determine the source of the oil leak. Although there was a weld fracture along the edge of the cooler housing, the fracture location and appearance were consistent with impact-related damage. The weld was repaired and there were no leaks observed with the oil cooler or the two transfer flex-hoses when they were pressurized and submerged in a water tank.

A review of photos taken on the day of the accident revealed that there was engine oil present on several components inside the engine nacelle. The internal surface of the eductor mixing duct also was oil wetted, consistent with engine exhaust drawing escaped oil from the nacelle through the annulus and into the mixer duct.

The oil cooler was replaced 2 days and 1.74 flight hours before the accident flight. Although an inadequately torqued oil flex-hose fitting likely was the source of the inflight loss of engine oil, the investigation was unable to conclusively support this scenario with the information collected during the investigation.

Text from the NTSB. Open the NTSB docket for CEN19LA231 for the full record.