NTSB Identification: DFW05CA088.
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Accident occurred Sunday, March 13, 2005 in Galliano, LA
Probable Cause Approval Date: 06/08/2005
Aircraft: Bell B-206L-1, registration: N480RA
Injuries: 1 Serious.
NTSB investigators used data provided by various entities, including, but not limited to, the Federal Aviation Administration and/or the operator and did not travel in support of this investigation to prepare this aircraft accident report.
The 1,514-hour pilot landed and remained parked on a platform in the Gulf of Mexico for approximately 10 minutes with the main rotor RPM at ground idle. While parked, the pilot grabbed the flight manifest and placed it in his lap to make an entry. While his head was down making the entry, the pilot had a sensation that the helicopter was "rocking backwards", and he grabbed both controls in an effort to "level" the helicopter. The pilot lifted up on the collective and pushed forward on the cyclic. The tail boom separated from the fuselage and both sections of the helicopter fell off the platform and into the water. Bell Helicopter Operations Safety Notice (OSN 206L-82-4), addressed tail boom skin compression wrinkles in all Bell model 206L/L-1/L-3 helicopter operations. The Notice stated, "Past 206 experience and flight tests...have revealed the tail boom 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 touch down. This can cause a resonant response that can damage the tail boom and or aft of the fuselage. Touch down rotor RPM above 70 percent RPM 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 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 tail boom separated forward of the horizontal stabilizer, consistent with an autorotation/low RPM failure.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The pilot's abrupt input of the collective while the main rotor RPM was at idle, which resulted in a separation of the tail boom.
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