Accident Overview
On 25 July 2010 at 10:00 local time, a Schweizer 269C helicopter, registered F-GJGQ, operated by an aerial work company, departed from the helipad at Saint-Aignan (Loir-et-Cher, France) for a ferry flight to Le Breuil (Allier) where it was to perform joyrides at an airshow. After approximately 10 minutes of flight, under visual meteorological conditions, the helicopter struck the tops of trees in a wooded area and crashed. The pilot, aged 26, held a Commercial Pilot License (Helicopter) issued in 2009 and had about 335 flight hours, including 220 hours on type. The passenger also died. The helicopter was destroyed.
Maintenance History
The owner, who also served as the pilot and a certified mechanic (with an Individual Maintenance Declaration issued by GSAC in 2006), performed the maintenance in accordance with the TRANS HELI maintenance program approved by GSAC on 29 January 2003. He reported that on 4 July 2010, 65 flight hours before the accident, he conducted a 300-hour inspection per the manufacturer's documentation. This inspection included visual checks of the three drag dampers (critical components per the type certificate) and an elongation test to verify their response to dynamic flight loads. The owner stated the test results were satisfactory, and he reinstalled the dampers and signed the return-to-service approval.
Technical Findings
Examination of the wreckage revealed that one of the three drag dampers had broken. Technical analysis of the three dampers showed:
- The first damper, found broken, exhibited degraded and partial adhesion between the elastomer and the damper housing, as well as internal corrosion, pre-existing the accident.
- The second damper contained an aqueous fluid, inconsistent with the seal integrity of a new damper, and displayed identical adhesion and corrosion characteristics as the first.
- Elongation tests on the second and third dampers showed values exceeding the maximum allowable limit.
These findings indicated that none of the three dampers were likely in an airworthy condition before the accident. During the flight, the adhesion degradation in the broken damper progressed to a point where it could no longer absorb normal vibration levels in forward flight. This led to excessive motion of the associated blade, causing a sudden main rotor imbalance that made control of the helicopter difficult and prevented continued flight.
Accident Sequence
The pilot likely attempted an autorotation for an emergency landing. However, the helicopter was over a wooded area, struck the tree canopy, and fell about 10 meters to the ground. The low rotor energy at impact, evidenced by minor rotor damage and vegetation traces, supported this sequence. Examination of the engine, engine controls, flight controls, and transmission system revealed no malfunctions that could have contributed to the accident.
Conclusion
The accident was probably caused by the degradation of the elastomer adhesion in the drag dampers, which was not detected during the 300-hour maintenance. This led to the sudden in-flight failure of one damper and subsequent loss of control. The maintenance operation on a critical component, performed by a single mechanic without approval by another person or independent organization, may have contributed to the accident. Overflight of the wooded area increased the event's severity.