What happened
The flight was conducted as an instructional session intended to prepare a student pilot, who already held a rating, for a Flight Instructor Certificate. During the sortie, the crew practiced several autorotation approaches before bringing the helicopter down for a landing. Following touchdown, the instructor pilot (IP) and the student remained inside the aircraft engaged in a discussion when they heard a loud popping noise.
The IP exited the helicopter to perform an external inspection but reported finding no obvious irregularities or damage at that time. The crew reboarded and took off again to continue training. During a subsequent autorotation approach, the pilot lowered the collective control after touchdown. Immediately upon contact with the ground, the helicopter pitched sharply to the left and forward. This motion caused the main rotor blades to strike the ground and subsequently impact the tail boom.
The investigation
A thorough examination of the aircraft revealed that the left front shock strut damper assembly, identified by part number 269A3150-5, had failed. The component had accumulated a total operating time of 3,614 hours prior to the incident. A metallurgical analysis of the failed part identified a single overload fracture located at the clevis on the piston end of the damper. The certified flight instructor (CFI) stated that no hard landings had been reported prior to this event.
Findings
The failure of the shock strut damper allowed excessive movement of the landing gear assembly during the final phase of the autorotation. This mechanical failure contributed directly to the uncontrolled pitch attitude of the helicopter upon touchdown, leading to ground contact with the rotor system and the tail boom.