CEN13LA321

The helicopter was on its first flight after extensive maintenance. As the pilot approached a canal at an altitude of about 20 feet, he heard a noise and then a loud "pop." The helicopter then started to spin to the right and the pilot was unable to stop the spin. After about two revolutions, the pilot reduced engine power to idle, and the helicopter collided with terrain and water. Examination of the helicopter revealed that the connection between the tail rotor drive shaft and the tail rotor gear box was partially separated. Of the two bolts that connected the drive shaft to the coupling on the gear box, one remained secured by its associated nut; however, the other bolt had backed out of the drive shaft, but remained in the coupling, and its corresponding nut was missing. The helicopter had accrued about 0.7 flight hours since its most recent maintenance, which included removing and reinstalling the tail rotor gear box. It is likely that the maintenance personnel did not ensure adequate torque of a tailrotor drive shaft coupling bolt, which allowed it to be back out of the drive shaft.

On June 6, 2013, about 1115 central daylight time a Bell 206-L4 helicopter, N720RL, impacted terrain, following the loss of tail rotor effectiveness, near Abbeville, Louisiana. The commercial rated pilot and passenger were not injured, and the helicopter sustained substantial damage. The helicopter was registered to HLW Aviation, LLC and operated by H&M Aviation, Inc. under the provisions of 14 Code of Federal Regulations Part 91 flight. Day visual meteorological conditions prevailed for the flight which operated without a flight plan. The flight originated from the Abbeville Chris Crusta Memorial Airport, (KIYA), Abbeville, Louisiana, about 1040. According to the pilot, he departed the airport to the southwest and approached a canal, to pick up water. At an altitude of about 20 feet, he heard a noise and then a loud "pop". The pilot added, the helicopter then started to spin to the right and that he lost tail rotor authority. After about two revolutions, he reduced the engine power to idle and the helicopter impacted terrain and water. Examination by the responding Federal Aviation Administration (FAA) inspector revealed that the helicopter had settled into about 3 feet of water. The aft section of the tail boom appeared buckled, with the drive shaft cover slightly twisted. After the helicopter was recovered from the water, the tail rotor driveshaft cover was removed. Examination of the drive shaft revealed that the coupling between the drive shaft and tail rotor gear box was only connected by one bolt. Of the drive shaft’s two bolts, one remained with its associated nut; however, the other bolt had backed out of the drive shaft, but remained in the coupling; its corresponding nut was missing. A review of the helicopter’s maintenance records revealed that the helicopter had undergone extensive maintenance, including removing and reinstalling the tail rotor drive and hub assemblies. The accident flight was the first flight after maintenance and lasted about 0.7 flight hours.