Incident Overview
A helicopter conducting an emergency landing experienced a loss of anti-torque control and subsequently came to rest on its right side. The pilot had reported a hydraulic system failure and diverted to the nearest airport.
Sequence of Events
During the emergency landing, after the helicopter slowed and descended through 100 feet, it yawed to the left. The pilot attempted to apply right pedal but encountered more force than expected to move the anti-torque pedals. Despite efforts to maintain a level attitude, the pilot could not stop the helicopter from spinning. Upon touchdown, the helicopter 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, with the engine continuing to operate. The main rotor blades repeatedly impacted the ground until the fire department shut down the engine by directing foam into the engine intake. The pilot then turned off the electrical master switch and exited the helicopter.
Aircraft Information
The helicopter involved was an AS350 B3, which is equipped with four servo actuators—three for the main rotor system and one for tail rotor blade pitch control. According to the flight manual emergency procedures, without hydraulic pressure, the anti-torque pedal operating force is very high.
Post-Accident Examination
Examination of the wreckage revealed that the hydraulic test switch was depressed. Activation of this switch during flight dumps hydraulic pressure, mirroring a hydraulic system failure. No other anomalies were found with the hydraulic system during testing.