What happened
On June 16, 2004, a Robinson R-22 Beta helicopter, registration EC-GVR, was conducting a mountain flight training session near Cerro de Valdemartín in the Sierra de Guadarrama, Madrid. The flight, operated by Aérea Aviación, carried an instructor and a student pilot with approximately 79 flight hours.
After performing several maneuvers and observing local wind conditions, the student pilot attempted a takeoff from a slope. During this maneuver, the aircraft entered an uncontrolled right turn, accompanied by a drop in rotor RPM and the activation of the low-RPM warning alarm. The instructor immediately took control and applied full left pedal, but the helicopter continued its descent and the left skid struck the ground. The impact caused the aircraft to overturn onto its left side.
The investigation
The investigation focused on the aerodynamic performance of the Robinson R-22 Beta at high density altitudes and the flight controls applied during the incident. Investigators examined the aircraft's weight and balance, noting the takeoff weight was approximately 1,280 lb. Meteorological data from the Navacerrada observatory confirmed winds of up to 14 knots from the north.
Analysis of the flight manual and performance charts revealed that the operation was being conducted at a pressure altitude of approximately 6,580 ft. The investigation also reviewed the flight school's training syllabus, which included mountain flight maneuvers at altitudes exceeding 2,000 m.
Findings
- The primary cause of the lateral loss of control and subsequent impact was a decrease in rotor RPM that was not immediately corrected by lowering the collective pitch.
- The aircraft was operating at a high density altitude, near the maximum limits for performing a hover without ground effect at that weight and temperature.
- The student pilot's lack of experience in mountain flight operations likely led to control inputs that increased the angle of attack, further demanding power that was unavailable at that altitude.
- A wind gust from the left may have reduced tail rotor effectiveness, contributing to the initial rightward yaw.
- The flight school's training materials emphasized the use of the throttle in mountain environments but did not sufficiently emphasize that the immediate pilot response to any RPM decay must be to lower the collective.