NTSB Identification: LAX94LA017.
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Accident occurred Monday, October 18, 1993 in BECKWOURTH, CA
Probable Cause Approval Date: 10/20/1994
Aircraft: AEROSPATIALE SA-315, registration: N49511
Injuries: 1 Serious.

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

THE PILOT WAS CONDUCTING AN EXTERNAL HELICOPTER EXTERNAL LOAD LOGGING OPERATION. AFTER RAISING TWO LOGS, THE PILOT HEARD A LOUD 'THUNK' NOISE FOLLOWED BY AN UNCONTROLLED TURN TO THE RIGHT. THE PILOT WAS UNABLE TO MAINTAIN ADEQUATE ROTOR RPM BECAUSE HE COULD NOT LOWER THE COLLECTIVE. EXAMINATION OF THE COLLECTIVE SERVO REVEALED IT TO HAVE INTERNAL LEAKAGE WHICH CAUSED A HYDRAULIC LOCK IN THE SERVO. THE SERVO EXTENSION AND RETRACTION TIME EXCEEDED THE MANUFACTURER'S SPECIFICATIONS.

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

was the worn collective servo causing a hydraulic lock and not allowing the pilot to lower the collective. This condition caused the main rotor blades rpm to decay.

Full narrative available

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