What happened
On October 29, 2025, at approximately 14:04 local time, a Mi-171 helicopter, registration OB-2019P, operated by HELISUR, crashed at the Malvinas Helipad (SPHM) in the Megantoni District, Cusco, Peru. The aircraft was performing an external load lifting maneuver using a 60-meter long-line to lift a 3,750 kg load.
During the lifting process, the crew initially lifted the load briefly before setting it back down. Upon attempting the definitive lift, the helicopter experienced a sudden loss of directional control. The aircraft entered an uncommanded anti-clockwise rotation, with the angular velocity increasing rapidly, and subsequently impacted the ground. The accident resulted in three fatalities, involving the pilot, co-pilot, and flight mechanic.
The investigation
The CIAA investigation examined flight data from the Flight Data Recorder (FDR), video footage from the helipad, and a physical inspection of the wreckage. Flight parameters revealed that while the initial stages of the lift were stable, a critical anomaly occurred at 14:04:24. At this moment, the tail rotor drive shaft position (TG rod) dropped abruptly from 277.4 mm to 254.7 mm and failed to respond proportionally to pedal inputs, even as the pilot applied maximum pedal pressure.
Physical inspection of the wreckage showed the main fuselage and tail section had separated due to high-energy impact. Investigators focused on the directional control system and identified a specific mechanical failure within the kinematic chain connecting the pedals to the tail rotor blades.
Findings
- The primary cause of the loss of control was the fracture of bellcrank (Part Number 184-5104-021), a critical component of the directional control system used by the crew to adjust tail rotor blade pitch.
- The failure of this bellcrank prevented the tail rotor from generating the necessary torque compensation, leading to the uncommanded rotation and subsequent impact.
- Flight data confirmed that the aircraft's engines and main rotor RPM remained relatively stable during the onset of the failure, indicating the issue was mechanical/control-related rather than a loss of engine power.