Amateur-built BABY BELLE N135PA accident near Stuart, Iowa

Probable cause

The failure of the tail rotor driveshaft for reasons that could not be determined due to the mechanically and thermally deformed fracture surface.

NTSB analysis

The private pilot was conducting a personal flight in the experimental, amateur-built helicopter. The pilot reported that, while he was maneuvering the helicopter about 400 ft above ground level, it yawed left, then suddenly "snapped" right, and then began spinning. The pilot attempted to regain control of the helicopter and was able to briefly stop the spin, but the spin then continued. The pilot subsequently conducted a forced landing to a cornfield, during which the helicopter impacted terrain and rolled over.

Examination of the helicopter revealed that the tail rotor driveshaft had failed during the flight, which resulted in a loss of control. The fracture surface of the driveshaft was mechanically and thermally deformed, and the failure mode could not be established. The pilot's medical and flight review were not current; however, the pilot's actions were not a contributing factor in the accident.

Text from the NTSB. Open the NTSB docket for CEN15LA412 for the full record.