Ayres S2R600 N3101S accident near Pine Bluff, Arkansas

Probable cause

The use of an incorrect mounting bolt by maintenance persons to attach the engine torque sensor, which resulted in an internal failure of the torque sensor and subsequent loss of engine power due to fuel starvation.

NTSB analysis

After the airplane sustained a complete loss of engine power during initial climb, the pilot performed an off-airport landing. Postaccident examination revealed that three teeth in the torque sensor spur gear separated after four of the five torque sensor mounting bolts became loose. The loose bolts caused the torque sensor housing to move radially away from the gear case, causing the teeth to overload and separate. Subsequently, the engine’s fuel pump and fuel control were no longer driven by the gears in the gear train, which were normally driven by the torque sensor spur gear, thus the engine was starved of fuel. Metallurgical examination showed that the bolts became loose because a bolt that was undersized and of the incorrect configuration had been installed. A maintenance record showed that the engine had previously been disassembled due to a torque sensor failure and an overhauled torque sensor had been reinstalled.

Text from the NTSB. Open the NTSB docket for CEN11LA460 for the full record.