What happened
On December 15, 2017, a Robinson R22 Beta, registration EC-JSC, was performing a flight test following a scheduled 100-hour maintenance inspection at Madrid/Cuatro Vientos Airport. The flight was operated by Intercopters Formación, S.L., with a pilot and a maintenance technician on board.
During the flight, the crew initiated an autorotation maneuver while on final approach. As the pilot reduced the collective and power, the rotor RPM began to decay below the required 97% threshold. In an attempt to recover the RPM, the pilot applied cyclic aft and pulsed the throttle, but the engine and rotor revolutions failed to recover.
In an effort to maintain airspeed and avoid trees in the flight path, the pilot transitioned to a forward cyclic attitude, maintaining a speed of approximately 80 kt. During the final stages of the descent, the pilot executed a sharp left turn to avoid approach lights, seeking a patch of soft ground. This maneuver, combined with a high-sink-rate descent, resulted in a violent impact with the ground approximately 300 meters from the runway threshold. The aircraft struck the terrain first with the tail rotor and the rear of the skids in a pronounced nose-high attitude.
The investigation
The CIAIAC investigation focused on the aircraft's mechanical systems, the flight trajectory, and the meteorological conditions. Investigators examined the carburetor heat system, the clutch system, and the freewheel unit, finding all to be in proper working order. The investigation also reviewed airport security footage, which showed the aircraft descending at a steep angle and high speed.
While the meteorological conditions (12°C with 93.6% relative humidity) were highly conducive to carburetor icing, the investigation determined that the pilot had correctly managed the carburetor heat, preventing ice formation. The investigation also analyzed the pilot's flight path, comparing the actual trajectory to the theoretical path required for a successful autorotation.
Findings
- The primary cause of the accident was the inadequate management of the autorotation maneuver.
- The pilot's decision to apply forward cyclic to increase airspeed was counterproductive, as it further decreased the rotor RPM and worsened the aerodynamic state of the aircraft.
- The pilot's attempt to maintain a high airspeed of 80 kt during the maneuver was an error in concept that contributed to the loss of control.
- A significant contributing factor was the rapid decay of the main rotor RPM and the limited altitude available to recover the maneuver.
- The two crew members sustained serious injuries during the impact.