NTSB Identification: NYC06LA121.
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Accident occurred Monday, May 29, 2006 in Goshen, NY
Probable Cause Approval Date: 06/27/2007
Aircraft: Eurocopter AS-350BA, registration: C-GGLM
Injuries: 2 Minor.

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

About 45 minutes into a cross-country flight, the helicopter experienced a hydraulic system failure. The pilot subsequently elected to perform a precautionary landing in a field. During the landing attempt, the pilot slowed the helicopter and it began to yaw left. The pilot attempted to correct the yaw, but was unable to overcome the "stiffness" of the right anti-torque pedal. The helicopter continued to yaw left, landed "hard," and rolled over. Examination of the helicopter's hydraulic system revealed that the hydraulic pump drive shaft splines and the attaching drive coupling splines were severely worn, to the point that they could no longer drive the hydraulic pump. Metallurgical hardness testing of both the drive shaft and the coupling revealed that the surfaces of the splines were below the manufacturer's specified hardness. Examination of the grease found trapped between the remaining portions of the hydraulic shaft pump splines revealed that it was hard packed and gray colored, suggesting that it had been in place for a significant period of time. The minimal amount of grease observed in the coupling sleeve did not satisfy the "generously filled" description referred to in the manufacturer's service bulletin, and required by a subsequent airworthiness directive. Examination of the helicopter's maintenance records revealed that since the issuance of the airworthiness directive, the helicopter had not been in compliance with either the calendar or flight time requirements. The helicopter's flight manual cautioned pilots operating the helicopter without hydraulic assistance, "Do not attempt to carry out hover flight or any low speed maneuver. The intensity and direction of the control feedback forces will change rapidly. This will result in excessive pilot workload, poor aircraft control, and possible loss of control."

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

Improper maintenance of the hydraulic pump/coupling, which resulted in a failure of the hydraulic flight control system. Factors included the substandard materials of the hydraulic pump drive shaft and coupling, and the pilot's failure to maintain an adequate airspeed during the landing.

Full narrative available

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