What happened
On March 25, 2012, an Aerospatiale AS 350B2 helicopter was performing sightseeing flights as part of a local spring festival near Gelsdorf, Germany. Shortly after takeoff, while the pilot was performing a right turn at an altitude of approximately 5 meters, the engine failed. The aircraft began to descend and struck the ground on the edge of a fire pond, landing on its fuselage.
The pilot attempted to clear a nearby fence and steer the aircraft into the pond to mitigate the impact. The pilot sustained serious injuries, while three passengers and one ground crew member suffered minor injuries. The helicopter was heavily damaged, and there was damage to the surrounding property.
The investigation
The BFU investigation focused on the mechanical state of the engine and the flight profile. Video footage from a spectator captured a flame appearing near the exhaust pipe approximately three seconds after takeoff, followed by flames trailing from the engine cowling during the descent.
An examination of the engine by the manufacturer in the United States revealed that a single gas producer turbine rotor blade had separated due to high cycle fatigue. This separation was likely caused by an abnormality in the blade coating. The resulting imbalance and intense vibrations caused the bolts on the fuel divider to loosen, leading to a fuel leak and subsequent fire in the engine nacelle. The investigation also found that the vibrations caused the rear bearing support housing welds to fracture.
Findings
- The primary cause of the accident was a mechanical engine failure caused by the fatigue separation of a turbine blade.
- The choice of the takeoff and landing site contributed to the severity of the accident. The site, located behind a local agricultural business, was not the location specified in the original flight permit.
- The takeoff profile was constrained by obstacles and loose items at the site, forcing a steep climb. This placed the aircraft in a flight regime (low altitude and low speed) that was unsuitable for a safe, controlled autorotation following an engine failure.
- The investigation noted that while the pilot was highly experienced, the operational environment presented risks that were not easily mitigated once the engine failed.