Eurocopter AS 350BA, Brooklyn, N.Y., May 4, 2004–The NTSB blamed the crash of Helinet Aviation Services’ WNBC News Chopper 4 on the pilot’s failure to maintain control after a loss of hydraulic system pressure. The Board labeled as factors the pilot’s misidentification of a hydraulic failure, his failure to perform the appropriate emergency procedure and the improper installation of the hydraulic pump belt by maintenance personnel.
With the helicopter not responding “the way it should be,” the 3,000-hour commercial pilot said he had experienced a “tail rotor failure.” Chopper 4 was seen entering a steep descent before quickly leveling off, then spinning around. It hit the roof of a four-story building.
Investigators found that the hydraulic pump drive belt was installed inside out and failed due to an overload, leading to a full hydraulic system failure. Eurocopter’s emergency procedures following a hydraulic system failure call for the pilot to “calmly reduce collective pitch and adjust airspeed to between 40 and 60 knots in level flight,” then cut off the hydraulic pressure by moving the toggle switch located on the collective pitch lever to off.
When the accumulators are exhausted, the control forces become significantly higher, but “not unmanageable.” The pilot would have to apply “non-negligible” forces substantially different from the forces required with the hydraulic system operating properly.
The Eurocopter factory training course for the AS 355 TwinStar that the pilot attended used a dual hydraulic pump system.
The pilot and a passenger were seriously injured and the helicopter was destroyed.