What happened
On July 25, 2010, a Schweizer 269 C helicopter, registration F-GJGQ, was being ferried from Saint-Aignan to Le Breuil for scheduled sightseeing flights. The flight was being conducted by a pilot accompanied by one passenger. Approximately ten minutes into the flight, under favorable visual flight conditions, the aircraft struck the treetops of a wooded area and crashed into the ground below.
Post-crash analysis of the wreckage revealed a nearly vertical final descent trajectory. Although the fuel tanks were damaged, approximately 40 liters of fuel remained. The relatively low energy of the rotors at impact, evidenced by minimal damage to the rotor blades and vegetation, suggested the aircraft was in an autorotative state prior to hitting the ground.
The investigation
The investigation focused on the integrity of the main rotor blade dampers, which are critical components designed to manage vibrations caused by Coriolis forces during forward flight. While the aircraft's owner—who also served as the certified mechanic—had performed a 300-hour maintenance inspection 65 hours prior to the accident, investigators found significant issues with the dampers.
Technical examinations of the three dampers revealed that one had physically ruptured. Furthermore, the second damper contained an aqueous liquid, indicating a loss of seal integrity. Testing showed that all three dampers exceeded their maximum allowable elongation limits. The investigation also determined that the ruptured damper suffered from internal corrosion and degraded adhesion between the elastomer and the housing.
Findings
- The primary cause of the accident was the sudden failure of a blade damper due to degraded elastomer adhesion, which created a severe rotor imbalance.
- This imbalance generated a sudden, uncontrollable vibration (imbalance) that made continued controlled flight impossible.
- The pilot likely attempted an emergency autorotation, but the flight path over a wooded area prevented a safe landing, leading to the collision with trees.
- The maintenance inspection performed 65 hours earlier failed to detect the internal degradation and corrosion within the dampers.
- The fact that the maintenance and subsequent release to service were performed by a single individual, without independent verification, was a contributing factor to the undetected component failure.