History of the Flight
On 7 June 2019 at approximately 10:00 local time, a Guimbal Cabri G2 helicopter, registered F-HOLA, was conducting an introductory flight at Grenoble Le Versoud aerodrome (Isère). The instructor, seated in the left seat, was accompanied by a student. The helicopter was flown in forward level flight from the parking area to Final Approach and Take Off (FATO) 04. While slowing down to enter hover, the collective stick suddenly separated from its base. The helicopter yawed left and upward. The instructor, who retained partial control via the cyclic and rudder pedals, attempted to counter the rotation and keep the helicopter level. Rotor rpm decreased, and the helicopter descended. The tail boom, followed by the skids, collided with the ground. The helicopter slid and came to rest in the grass at the right edge of the runway. Both occupants evacuated uninjured.
Additional Information
Meteorological Conditions
At the accident site, wind was 10 kt from the north-east, and conditions were CAVOK.
Crew Experience
The instructor held a commercial pilot license (CPL(H)) and helicopter instructor rating (FI(H)), with approximately 6,500 flight hours, including 1,200 hours on type. The student had completed two hours of theoretical training as part of an introductory course; this was the first flight of practical training.
Helicopter Examination
Examination revealed damage from the ground impact. No anomalies were found on the engine or power transmission components to the main rotor or fenestron. The left-seat collective stick had come out of its base, with no signs of wear on the base or stick. The fenestron blade pitch control indicated the instructor was applying full right pedal at impact.
Video Recording
A video from a witness showed the flight phases from take-off through forward flight to the collision. The loss of control occurred while the helicopter was slowing near FATO 04 in near-hover and descending slightly. Suddenly, the helicopter banked left, entered a nose-down attitude, and yawed about 45° left. It rose a few meters, made two full rotations around the yaw axis, then descended and hit the ground.
Dual Collective Control System
The dual collective control consists of a stick and base with a locking sleeve. The stick locks into place via four balls fitting into holes at the stick end. A silver ring limits sleeve travel. The flight manual describes installation: 'maintain the locking sleeve pushed while plugging the stick. Rotate the stick until the sleeve locks.' Pre-flight checks include checking removable controls.
Tests showed that if the sleeve is not pushed back, the stick inserts only partially. If inserted without rotating, non-locking can be detected by stick rotation and a 2-3 mm gap between sleeve and ring. However, the uniform black color of the base and sleeve hinders visual detection of incomplete locking.
Other Information
On the previous flight, a student pilot had removed the dual controls for a solo flight and later refitted them. His instructor visually checked the assembly but did not detect the anomaly. The accident instructor also performed a visual pre-flight check and a control deflection test after start-up, noting no anomaly.
Conclusions
The separation of the collective stick from its base on the left-seat side during deceleration to hover led to loss of control and subsequent collision. Contributing factors were an incomplete inspection of the assembly when the dual controls were reinstalled after the previous flight, an inadequate visual check during pre-flight, and the uniform color of the assembly hampering anomaly detection.
Safety Measures
The operator issued reminders on procedures for verifying removable components and flight manual procedures, and a service memo stating that dual controls shall only be fitted by the instructor involved in the flight. The manufacturer issued Service Bulletin SB 19-015 A on 6 December 2019, requiring markings on the left-seat collective control to allow visual detection of incorrect assembly.