NTSB Finds Procedures, Systems At Fault In Fatal Helicopter Crash
The pilot of an Airbus AS350 helicopter that crashed in July 2015 failed to perform a preflight hover check, the NTSB said in a synopsis of its probable-cause report on Monday. If he had performed the hover check, as required by operational procedures, he could have found that he hadn’t returned the yaw servo hydraulic switch to its “On” position after completing preflight checks on the ground. This resulted in a lack of hydraulic pressure in both the tail rotor servo control and the yaw load compensator accumulator, a lack of hydraulic boost to the pedals and significantly increased pedal loads. Surveillance videos capturing the liftoff show that the helicopter yawed to the left and rotated counterclockwise several times before descending and impacting a recreational vehicle and the parking lot. The impact forces were survivable, the NTSB said, but the helicopter then caught fire. The pilot was killed, the two flight nurses on board were seriously injured and the helicopter was destroyed.
The NTSB determined that the probable cause of this accident was the preflight hydraulic check, which depleted hydraulic pressure in the tail rotor hydraulic circuit, and the lack of salient alerting to the pilot that hydraulic pressure was not restored before takeoff. Such alerting might have cued the pilot to his failure to reset the yaw servo hydraulic switch to its correct position during the preflight hydraulic check. Instead, the mistake resulted in a lack of hydraulic boost to the pedal controls, high pedal forces and a subsequent loss of control after takeoff. Contributing to the accident was the pilot’s failure to perform the hover check, which would have alerted him to the pedal control anomaly at an altitude that could have allowed him to safely land the helicopter. Also contributing to the severity of the injuries, the NTSB said, was the helicopter’s fuel system, which was not crash-resistant and facilitated a fuel-fed post-crash fire.