WPR11GA144 · Eurocopter AS 350 B2

The flight instructor had briefed the flying pilot that he wanted him to perform a maximum performance takeoff simulating a 20- to 25-foot obstacle and that he was going to simulate a hydraulic failure during the maneuver by activating the hydraulic test switch. Prior to performing the maneuver, the pilot confirmed with the instructor that once the hydraulic failure warning activated he would accelerate to 40 knots before activating the hydraulic isolation switch. The instructor would need to reset the hydraulic test switch prior to the pilot activating the hydraulic isolation switch. After the briefing, the pilot initiated the maximum performance takeoff, and as the helicopter attained 20-25 feet, the instructor activated the hydraulic test switch. The pilot stated that as soon as the test switch was activated, he could no longer input right pedal because the control forces were too great. The helicopter began to yaw to the left, and the pilot then activated the hydraulic isolation switch because he thought the helicopter would be more controllable. The pilot did not consider that the hydraulic fluid had been evacuated from both the tail rotor accumulator and the yaw load compensator actuator due to the activation of the hydraulic test switch by the instructor, and the test switch had not yet been reset. As a result, the hydraulic boost from the normally closed yaw load compensator system was unavailable. The helicopter continued to yaw to the left and developed into a spin about its vertical axis. The instructor told the pilot to “fly the helicopter” and was hoping the pilot would recover from the loss of control condition. The pilot attempted to recover by following the direction of the nose of the helicopter to try to gain airspeed. The instructor attempted to intercede by inputting right cyclic, but since the pilot was applying left cyclic, the cyclic inputs were ineffective. The helicopter spun around several times before impacting the taxiway. According to the training procedure for a loss of hydraulic pressure, the instructor should have reset the hydraulic test switch prior to the pilot activating the hydraulic isolation switch. This flight manual specific sequence of switch selections and corresponding actions when simulating a hydraulic system failure were not followed by the pilots. Postaccident examination of the helicopter systems, including the hydraulic system, revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.

Verbatim NTSB analysis and probable cause from the NTSB dataset