NTSB Identification: LAX08IA042
14 CFR Part 91: General Aviation
Incident occurred Friday, December 14, 2007 in Fresno, CA
Probable Cause Approval Date: 12/24/2008
Aircraft: Eurocopter France AS350 B3, registration: N414HP
Injuries: 2 Uninjured.
NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.
The certified flight instructor (CFI) configured the helicopter for a practice emergency maneuver with the hydraulic system off. Upon disengaging the hydraulics, he immediately noticed that an abnormal force was required on the cyclic control to prevent the helicopter's nose from pitching up and to the left. He elected to continue the landing with the hydraulics off and began to slow the airspeed as the helicopter adjoined final approach. He was convinced that he would not be able to land the helicopter without it incurring damage due to the severe control restriction. He managed to complete a run-on landing without mishap by maintaining an airspeed of about 10 kts. When the helicopter came to rest, the pressure was released on the cyclic and the second pilot restored the hydraulics via the collective switch. Immediately thereafter, the cyclic began a hard over and displaced to the left against the CFI's leg. He attempted to center the cyclic with both hands, but he was unable to move the control. After 40 seconds the pressure released and the second pilot centered the cyclic with ease. The hydraulic servos were tested and a complete teardown of each servo was performed. The pressure testing of one of the servos revealed that the unlocking pressure was out of tolerance (too high). Upon disassembly of this servo, wear was observed on the conical surface of the locking finger and on the diameter in contact with the bearing. According to the servo manufacturer, the wear resulted in excessive friction in the bearing, which led to the high unlocking pressure.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: Malfunction of a hydraulic servo while on final approach due to excessive wear of the locking finger. Full narrative available
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