What happened
On August 15, 2011, a Bell 206L-3 helicopter, registration SE-HVI, was engaged in aerial work to suppress dust at the Aitik mine in Norrbotten county. Operated by Fiskflyg AB, the mission involved using "Bambi Bucket" water containers to spray water on a tailings dam.
During the operation, the pilot attempted to refill the container in a small tarn. As the pilot increased the collective to lift the heavy, water-filled bucket out of the water, the aircraft experienced a sudden, violent leftward bank accompanied by a significant rise in the nose. Despite the pilot's attempts to correct the roll with full right cyclic and lowering the collective, the aircraft entered a high-speed rotation around its axes and crashed into the water. The pilot sustained minor injuries and was able to exit the wreckage alone.
The investigation
SHK investigators examined the wreckage and the aircraft's landing gear design. The technical analysis focused on the physics of the rotation and the state of the aircraft during the lift. Investigators also reviewed the pilot's work environment, the company's safety culture, and the specific challenges posed by the flight site, which featured tall trees near the approach path.
Findings
- The investigation established that a cable from the water container had become caught over the rear part of the left landing gear skid and skid shoe.
- This entanglement caused the center of gravity to shift far outside the designed operational limits.
- The primary cause of the accident was that the position of the water container was not verified before the lift was initiated.
- Environmental factors, specifically sun reflections and shadows, hindered the pilot's ability to monitor the bucket's position via the rear-view mirror.
- The landing gear design, specifically the straight rear section of the skid and the mounting elements, allowed the cable to become hooked.
- The high demands of navigating the small water area near trees contributed to the difficulty of the maneuver.
Safety action
SHK issued recommendations to the Swedish Transport Agency and EASA, stating that operators must establish specific operational limitations that account for the risks of the helicopter's design when performing missions with suspended loads.