Incident Overview
A commercial pilot was performing a hydraulic accumulator test as part of the before-takeoff checks when the helicopter inadvertently lifted off. During the test, the hydraulic pressure had been bled off, and the pilot could not regain control of the helicopter prior to it impacting the ground tail rotor first.
Collective Lock Design
The collective was locked down during the accumulator test; however, it became unlocked when the pilot was repositioning his hands to restore hydraulic power after the test. FAA inspectors indicated that the collective lock design allowed for the release of the collective when the cyclic was moved during the test with the hydraulic pressure depleted.
Sequence of Events
The pilot initiated the hydraulic accumulator test as part of standard pre-takeoff procedures. The test required bleeding off hydraulic pressure. During this process, the collective was locked in place. After completing the test, the pilot began to reposition his hands to restore hydraulic power. At that moment, the collective lock disengaged, likely due to movement of the cyclic, which the lock design permitted when hydraulic pressure was absent. The helicopter lifted off unexpectedly, and the pilot was unable to maintain control, leading to a tail rotor first impact with the ground.