What happened
During a takeoff attempt, a helicopter experienced a loss of sufficient power to maintain flight, necessitating a forced landing. At the time of the incident, the aircraft was operating within its published maximum takeoff weight (MTOW) and was within the established limits for high-altitude, high-temperature (HIGE) operations. While the pilot noted a 10 kt headwind component, the wind was characterized by variable directions and gusting strengths.
The investigation
The investigation examined the aircraft's performance and the environmental variables present during the departure. It was noted that the engine was delivering power to the rotors, and no unusual vibrations or noises were detected during the initial phase of takeoff. The rotor speed remained within operational limits. The investigation focused on how the interaction between the aircraft's weight, the ambient temperature, and the fluctuating wind conditions contributed to the power deficit.
Findings
- The aircraft's all-up weight (AUW) was below the published MTOW.
- The forced landing resulted from power required to continue flight being in excess of power available given the specific combination of takeoff weight, temperature, and wind conditions.
- Two primary scenarios were identified that could lead to insufficient power: a shift in wind direction to the right, which would increase the demand for left tail rotor pedal and reduce power available for main rotor thrust, or a reduction in headwind strength immediately after translational lift, which would move the aircraft into a HOGE (hover out of ground effect) flight regime.