GAA19CA279 · Guimbal CABRI G2

The flight instructor reported that, during a training flight in the helicopter, he briefed the student pilot on the procedures required to land with a simulated stuck left pedal. The student began a descent to enter a shallower-than-normal glidepath to the runway surface, and he completed his final checks for the maneuver and continued the approach. During the approach the flight instructor directed the student pilot to use "throttle manipulation to control the yaw caused by a fixed input on the anti-torque system." Upon contacting the runway, the helicopter veered left, and the instructor chose to abort the landing. As the helicopter lifted off, it began to rapidly yaw left while drifting left of the runway. Recognizing that the helicopter was in a spin, they attempted to correct by leveling the helicopter long enough to regain tail rotor authority. The helicopter's left skid impacted mud on the left side of the runway, and the helicopter rolled onto its left side. The helicopter sustained substantial damage to the main rotor, fuselage, and tailboom. The instructor reported that there were no preaccident mechanical failures or malfunctions with the helicopter that would have precluded normal operation. A manufacturer's service letter, SL 19-002 A, stated, "During in-flight tail rotor control failure simulation, pilots should never use the twist grip to control yaw." Therefore, the flight instructor's direction to the student to use the throttle to correct the yaw was incorrect and led to ground impact and a dynamic rollover.

Verbatim NTSB analysis and probable cause from the NTSB dataset