NTSB Identification: LAX02TA299.
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Accident occurred Sunday, September 29, 2002 in Bishop, CA
Probable Cause Approval Date: 06/08/2005
Aircraft: Eurocopter AS350-B3, registration: N352SA
Injuries: 4 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this public aircraft accident report.

The helicopter was performing a hydraulic actuator check for the first flight of the day. The collective had been placed in the down position, the collective lock was engaged, and the rotor powered up to 100 percent flight idle. After depressing the hydraulic test switch, the pilot moved the cyclic fore and aft to confirm there was pressure remaining in the accumulators for a few control movements. The collective rose uncommanded and the helicopter moved forward in a nose down attitude. The main rotor struck the ground and the helicopter made two revolutions before rolling over onto its side, destroying both the main and tail rotor systems. A small fire ensued in the exhaust area, but was quickly extinguished. Examination of the collective locking mechanism (P/N 350A-27 3455-20 and P/N 350A-27 3107-26) found that it failed to hold the collective in the full down position due to wear on the locking tab. During servo accumulator checks, movement of the cyclic control after accumulator depletion caused the collective to move due to feedback in the control system. The locking device disengaged and the collective increased causing the aircraft to move.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

the disengagement of the collective locking mechanism due to component wear.

Full narrative available

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