Hughes 269C N380TL accident near Phoenix, Arizona

Probable cause

A loss of tail rotor drive due to a fatigue failure of the main transmission pinion, which resulted in a loss of directional control during cruise flight.

NTSB analysis

When the pilot was about 2 minutes from reaching his destination at an altitude of about 500 feet above ground level (agl), he detected a vibration coming from the back of his seat and in the anti-torque pedals. This was followed by a right yaw that was not correctable with pedal input. As the pilot attempted to maintain level flight he heard a "metallic clunking" behind him. He then looked over his shoulder and saw what he thought was the tail rotor slowing down. Able to maintain forward flight by countering the right yaw with left cyclic input, the pilot located a cul-de-sac in a residential neighborhood in which to land. He lowered the collective, rolled off throttle, and made a slight right turn toward the cul-de-sac. During the landing the helicopter impacted the roof of a house, then a brick wall that separated the house from the adjoining residence. The helicopter came to rest in the backyard of the adjacent home. Witnesses reported that the helicopter didn't sound right, that the engine was sputtering, and that its speed was increasing and decreasing. It was observed rocking and teetering, and then nose-dived toward the ground. After the helicopter crash landed, the engine continued to run and the tail rotor continued to spin. A post-accident investigation revealed that the main transmission pinion had failed from fatigue. Subsequent to the fracture of the main transmission pinion, the tail rotor drive shaft would have been free to move, resulting in the loss of the tail rotor drive. Maintenance records revealed that the main transmission pinion was part of a periodic inspection check, which was completed the day prior to the accident.

Text from the NTSB. Open the NTSB docket for WPR12FA191 for the full record.