Final Report: Abrupt Collective Input Downed Bell
Bell 206L-1 LongRanger, Galliano, La., March 13, 2005–Parked on a platform in the Gulf of Mexico for approximately 10 minutes with the main rotor rpm at ground idle, the commercial pilot had his head down making an entry on the flight manifest. He had a sensation that the helicopter was “rocking backwards” and grabbed both controls in an effort to “level” the helicopter. He lifted up on the collective and pushed forward on the cyclic. The tailboom separated from the fuselage, and both sections of the helicopter fell off the platform and into the water. The pilot was seriously injured. The NTSB said the probable cause of the accident was the pilot’s abrupt input of the collective while the main rotor rpm was at idle.
Bell Helicopter Operations Safety Notice 206L-82-4 said, “the tailboom and aft fuselage can be damaged if during an autorotation landing the main rotor rpm is allowed to decay below 70 percent rpm. Applying collective pitch in excess of that required will in some instances result in excessive flapping of the main rotor during or after touchdown. This can cause a resonant response that can damage the tailboom and/or aft of the fuselage. Touchdown rotor rpm above 70 percent is preferred. Upon ground contact collective pitch should be reduced smoothly without delay while maintaining cyclic pitch near the center position. Long ground runs with the collective up, or any tendency to float for a long distance prior to skid contact should be avoided.”
When asked how this accident could have been prevented, the Rotorcraft Leasing operator stated, “Pilot should have remained more vigilant in monitoring control input and position. More aggressive use of control friction would have minimized the possibility of this occurrence.”
Examination of the wreckage revealed the tailboom separated forward of the horizontal stabilizer, consistent with an autorotation/low rpm failure.