Amateur-built V35 N6245V accident near Monroe, Wisconsin

Probable cause

A total loss of engine power due to the failure of the Nos. 5 and 6 connecting rods from a lack of oil lubrication for reasons that could not be determined.

NTSB analysis

The private pilot and passenger were en route on an instrument flight rules flight when the engine lost oil pressure, followed by a total loss of engine power. The pilot declared an emergency with air traffic control and stated that he “had an oil pressure event there but it’s building back up so standby.” The controller cleared him direct to the nearest airport and asked the pilot if he need any assistance at the airport, which the pilot declined. Flight track data showed that the airplane began a shallow descent toward the diversion airport before the data ended about 2 minutes later. The pilot stated that he flew directly over the airport and was unable to see it due to oil on the windshield and smoke in the cabin; he eventually performed a forced landing in a field about 4 nautical miles from the diversion airport.

A postaccident disassembly examination revealed a large hole in the top of the engine crankcase above the No. 6 cylinder. The inside of the engine contained a significant amount of metallic debris. The Nos. 1 through 4 connecting rods remained attached to the crankshaft, but all exhibited significant heat distress from a lack of oil lubrication. The Nos. 5 and 6 connecting rods fractured at the bearing and sustained damage from impacting the crankshaft, cylinder walls, and the inside of the case. The ends of the Nos. 5 and 6 connecting rods and their bearings were not found or identified within the available metallic debris. It is likely that the Nos. 5 and 6 connecting rods failed due to a lack of oil lubrication; however, the reason for the oil loss could not be determined. The continued operation of the engine after the loss of oil pressure likely contributed to and aggravated the amount of damage to the engine.

Text from the NTSB. Open the NTSB docket for CEN19LA290 for the full record.