What happened
During an emergency landing, a AS3D B3 helicopter impacted a taxiway following a loss of anti-torque control. The pilot had diverted to the nearest airport after reporting a hydraulic system failure. As the aircraft descended through 100 feet and slowed for landing, it began to yaw to the left. Although the pilot attempted to apply right pedal, the force required to move the anti-torque pedals was significantly higher than expected.
The pilot attempted to maintain a level attitude but was unable to stop the helicopter from spinning. Upon touchdown, the aircraft rotated on the ground until the right landing gear skid collapsed and the main rotor system struck the ground. The helicopter came to rest on its right side. During the event, the engine remained operational, and the main rotor blades repeatedly struck the ground until firefighters suppressed the engine by directing firefighting foam into the intake. The pilot successfully deactivated the electrical master switch and exited the aircraft; the pilot was not injured.
The investigation
The AS350 B3 is equipped with four servo actuators: three for the main rotor system and one for tail rotor blade pitch control. Post-accident examination of the wreckage revealed that the hydraulic test switch had been depressed. While this switch is used during preflight inspections to test hydraulic accumulator pressure, its activation during flight dumps hydraulic pressure, creating a condition that mirrors a total hydraulic system failure. No other anomalies were found within the hydraulic system during post-accident testing.