What happened
On January 25, 2003, at approximately 06:10 UTC, a Hughes Schweizer 269 C helicopter, registration F-ODZT, was performing a routine repositioning maneuver at the Saint-Pierre Pierrefonds aerodrome in Réunion. The pilot was attempting to move the aircraft from its parking spot to a refueling station.
As the pilot began to increase power to lift off, the aircraft entered a period of significant vibration, which the pilot initially identified as a ground resonance phenomenon. Attempting to escape the discomfort of the vibrations, the pilot increased altitude into a hover. However, the vibrations persisted despite the aircraft being airborne. The pilot subsequently landed the aircraft, but as the engine power was reduced, the vibrations intensified dramatically, causing severe structural damage and the eventual destruction of the aircraft.
The investigation
The investigation focused on the aircraft's airframe, the main rotor head, and recent maintenance history. Investigators examined the landing gear, finding the rear shock absorbers properly inflated, while the front absorbers had deflated due to the impact.
Upon inspecting the main rotor, investigators found that the drag dampers for the yellow and blue blades were compromised. Specifically, the mounting bracket for the yellow blade's damper had suffered a static fracture, and the elastomeric cylinder had been ejected from its housing.
Further examination of the rotor head revealed that the blade sleeves for both the yellow and blue blades were abnormally tight. This condition was traced back to the maintenance process used when replacing the internal bushings (rings 1 and 2). The investigation determined that the technician had failed to secure the internal ring 3 during the extraction process, causing it to shift inward—a defect that is not visible to the naked eye but significantly restricts the blades' ability to move in drag.
Findings
- The aircraft was subject to an initial ground resonance event of undetermined origin.
- This event was severely exacerbated by a non-compliant maintenance procedure performed during a recent bushing replacement.
- The improper installation of the blade sleeves caused abnormal resistance to the drag movements of the yellow and blue blades.
- The resulting imbalance led to the sudden failure of the yellow blade's drag damper, which then triggered a divergent vibration process that destroyed the aircraft.