What happened
On December 12, 2016, a Robinson R20 helicopter, registration F-HALD, was engaged in a flight training mission near Tourrettes, France. The flight originated from Cannes Mandelieu aerodrome, with the instructor and student pilot proceeding to Fayence aerodrome to perform two circuit patterns. During the return leg, the instructor planned an instructional autorotation exercise with engine power recovery over a field.
During the descent, the student pilot maintained the controls while the instructor took over the flight path to perform the flare. The instructor initiated the flare at an altitude of approximately 30 to 40 feet. Upon increasing the collective pitch, the aircraft experienced a sudden 90-degree right yaw. Although the instructor applied rudder pedals to counteract the yaw and leveled the aircraft, the helicopter struck the ground. The skids impacted the terrain, with the right skid hitting more forcefully. The impact caused the aircraft to rebound, rotate 90 degrees to the right, and come to rest in a nose-up position, with the tail boom broken.
The investigation
The investigation focused on the mechanical state of the engine and the power regulation system. While the instructor reported that the engine stopped unexpectedly and noted that engine and rotor RPM reached 108%, which is above normal operating limits, no mechanical malfunctions were found in the wreckage. Specifically, examinations of the engine and the governor confirmed that the system was in good working order and met manufacturer specifications. The investigation noted that the governor is designed to regulate RPM within a range of 80% to 115% but cannot prevent overspeed or underspeed caused by abrupt flight maneuvers.
Findings
- The instructor performed the flare at an altitude lower than the 40 feet recommended in the flight manual.
- The effectiveness of the flare was likely reduced due to the low wind conditions present at the time of the accident.
- The instructor likely applied excessive power during the flare, which triggered the sudden 90-degree yaw.
- The low altitude at which the maneuver was performed left insufficient time for the pilot to recover control before ground contact.