Amateur-built RV7 N514BS accident near Henefer, Utah

Probable cause

The total loss of engine power due to the separation of the idler gear shaft bolts as a result of improper installation, which allowed for the idler gear to become disengaged.

NTSB analysis

The pilot reported that during the flight, he switched fuel tanks and shortly after, the engine began to sputter. The pilot turned on the electric fuel boost pump and switched the fuel selector valve to the original position, and the engine began to operate normally. However, a short time later, the engine quit, and despite his attempts, he was unable to restore engine power. The pilot initiated a forced landing to a nearby road during which the left wing struck the ground, the airplane veered to the left, exited the surface of the road, and impacted rising terrain.

Postaccident examination of the engine revealed that the crankshaft idler gear shaft was separated from its mount and the idler gear was disengaged from the crankshaft and camshaft. Fretting was observed within the area of the idler gear shaft mount. The idler gear shaft bolts were separated. No evidence of a locking plate or safety wire was observed. It’s likely that idler gear bolts had become loose due to improper installation, which allowed the idler gear shaft to shift and the idler gear to become disengaged from the crankshaft and camshaft, which would result in a loss of engine power.

Text from the NTSB. Open the NTSB docket for WPR20LA239 for the full record.