What happened
On November 1, 2007, a Robinson R22 helicopter, registration PT-YOU, was conducting a proficiency check flight near Mogi das Cruzes, São Paulo. The flight, operated by Goldenfly Taxi-Aéreo, was being evaluated by an ANAC Civil Aviation Inspector (INSPAC) to certify the pilot for a Commercial Pilot License (PCH).
The flight proceeded from Guarulhos to the area of the Mogi das Cruzes reservoir to perform training maneuvers. During the final autorotation exercise, the low rotor RPM warning horn sounded. Despite an attempt by the inspector to take control and restore normal flight by accelerating the engine, the aircraft could not recover and struck the ground before reaching the intended landing area. The two occupants sustained minor injuries, while the aircraft suffered substantial damage.
The investigation
CENIPA examined the flight sequence, the aircraft's technical condition, and the environmental factors. The investigation focused on the mechanics of the autorotation maneuver being performed at the time, which involved disengaging the governor to simulate a power-off descent.
Investigators evaluated three primary hypotheses for the loss of control: a low rotor RPM stall caused by high drag and high angle of attack; a vortex ring state induced by improper power application; and pilot error during the execution of the maneuver. The investigation also considered the meteorological conditions, noting that while winds were present, they could not be definitively identified as a contributing factor due to the lack of wind indicators at the non-homologated landing site.
Findings
- The pilot was qualified but possessed low flight experience.
- The pilot demonstrated a tendency to allow the airspeed to drop dangerously, reaching approximately 40kt during the descent.
- The pilot failed to maintain the collective in the proper position to preserve rotor RPM.
- The low rotor RPM contributed to a loss of aerodynamic effectiveness, making recovery via engine acceleration difficult or impossible.
- The flight planning and pilot judgment regarding the execution of the maneuver were inadequate.