What happened
During a training flight, the instructor pilot initiated a simulated engine failure scenario. In response, the student pilot executed a standard 180-degree autorotation maneuver to land the aircraft. As the helicopter approached the ground for the flare and final cushion phase of the landing, the pilot allowed the rotor RPM to decay below safe limits. The instructor pilot did not adequately monitor the student's use of the collective pitch control during this critical phase. Shortly after touchdown, a significant vibration was felt by the occupants, resulting in the failure of the tailboom structure.
The investigation
The examination focused on the mechanical integrity of the helicopter following the incident. The primary finding was the structural failure of the tailboom, which occurred immediately after the landing impact. The investigation noted that the rotor RPM had decayed during the flare, indicating a loss of energy in the rotor system at a critical moment.
Findings
The sequence of events indicates that the tailboom failure was caused by the excessive loads placed on the airframe due to improper control inputs during the landing. Specifically, the rotor RPM decay allowed the pilot to land with insufficient rotational energy, leading to a hard or uneven contact with the ground. The lack of monitoring by the instructor pilot regarding the collective pitch control contributed to the inability to prevent this unsafe landing condition.
Safety message
This incident highlights the importance of maintaining proper rotor RPM during autorotation landings and the critical role of the instructor in monitoring student pilot control inputs, particularly during the flare and touchdown phases.