NTSB Identification: LAX07IA115.
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Nonscheduled 14 CFR
Incident occurred Wednesday, March 28, 2007 in Kahului, HI
Probable Cause Approval Date: 06/30/2008
Aircraft: Eurocopter AS 350 BA, registration: N4010K
Injuries: 7 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.
While in cruise flight at 2,800 feet mean sea level (msl) approximately 100 knots airspeed, the pilot experienced an uncommanded left yaw. The pilot pressed each rotor pedal and "found they were not functioning." The pilot turned back to the airport and declared an emergency. The pilot attempted a run-on landing. During the landing, the helicopter "wanted to turn left as the airspeed slowed." Subsequently, the helicopter twice spun to the left and came to rest upright partially on the runway and adjacent grass. The loss of tail rotor control was due to the lower support yoke arm bushing being loose in the lower support yoke arm. During operation of the tail rotor controls, the looseness transferred the cyclic operational stresses, via the expansion pin assembly, to the upper support yoke arm, which failed in fatigue. Under continued operation, the pitch control input rod then translated upwards into the path of the rotating tail rotor gearbox input flange. The pitch control rod wore down until the input rod no longer transmitted operational forces and it separated with the sequential loss of tail rotor control. During a recent 500-hour inspection, a visual check on the expansible pin was performed; however, only one end of the expansion pin assembly appeared to have been visually checked. The manufacturer's maintenance manual does not specify how the installation check should be performed.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: The loss of tail rotor control due to wear damage to the pitch control input rod that resulted ultimately in the fatigue failure of the upper support yoke arm. Contributing factors were the improper maintenance inspection of the expansion pin assembly and the loose bushing in the lower support yoke arm. Full narrative available
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