Cessna 172RG N6520R accident near Tomahawk, Wisconsin

Probable cause

A total loss of engine power due to a loss of all of the engine's oil as a result of the safety wire on the governor idler gear shaft's oil plug breaking, leading to the oil plug coming unscrewed. Contributing to the accident was the lack of a suitable area for a forced landing.

NTSB analysis

The pilot reported that he noticed smoke in the cabin and turned back to the departure airport. Oil began to accumulate on the windshield, which obscured his forward visibility. He made a five-mile straight-in approach using the airplane's global positioning system. He said that he attempted to maintain 2,500 feet above mean sea level and began to lose engine power about three miles from the airport. The engine "sputtered then froze" about two miles from the airport. The pilot then made a forced landing on a field that the passenger saw out of his window. The pilot said that the airplane came to rest at the end of that field, where it impacted trees at about 30 knots. Subsequent to the accident the propeller and starter ring gear were removed. The oil plug on the nose of the engine case that covers the governor idler gear shaft was not in place and it was found in the cowling. A safety wire that had secured the oil plug was observed attached to engine case with a separation at its plug end.

Text from the NTSB. Open the NTSB docket for CHI08LA230 for the full record.