Incident Overview
During a lift-off from the top of a chemical truck, a helicopter pilot heard a faint whining sound that increased in volume before abruptly ceasing as the aircraft cleared the truck. Immediately afterward, the helicopter's flight controls became locked. Despite the restriction, the pilot was able to apply a small amount of aft cyclic input, which helped the helicopter settle toward the ground. Upon touchdown, the helicopter drifted to the right, skidded across the ground, and subsequently experienced a dynamic rollover.
Hydraulic Pump Failure
The pilot reported that the hydraulic pump, which supplies hydraulic power to the flight control system servos, had failed. A postaccident examination of the hydraulic pump was conducted; however, the pump had sustained impact damage during the accident sequence, preventing investigators from determining why the pump failed.
Previous History of the Hydraulic Pump
An FAA inspector reported that the hydraulic pump had been removed from a salvaged helicopter in 2000. It had not been used prior to its installation on the accident aircraft, which occurred approximately one and a half months before the accident. The inspector also noted that the pump's condition was unknown and that it was never tested before being installed on the helicopter.