What happened
On January 6, 2001, an Aerospatiale AS 350 B2 helicopter, registration SE-JGK, was performing lime seeding operations near Sör-Mesjön, northwest of Örnsköldsvik, Sweden. After completing several loads, the pilot landed to refuel the aircraft. During the refueling process, the engine remained running.
Upon departure, the pilot attempted to enter a right-hand circuit to approach the loading station. While flying at approximately 30 meters above the ground in the downwind portion of the circuit, the engine suddenly failed. The pilot initiated an autorotation, but due to the low altitude and airspeed, the aircraft struck treetops before impacting a road in a wooded area. The helicopter slid into a roadside ditch and tipped onto its side. A severe fire broke out shortly after the impact. Although the pilot was initially trapped with a leg jammed in the wreckage, they managed to escape before the flames consumed the aircraft.
The investigation
Investigators from the Swedish Accident Investigation Authority (SHK) examined the wreckage and the engine. While much of the aircraft was destroyed by fire, technical analysis was conducted on the surviving components. The investigation focused on the engine's fuel system to determine the cause of the flameout.
Engine components were sent to the manufacturer in France for specialized testing. While a definitive technical fault could not be identified with absolute certainty due to fire damage, investigators discovered that the fuel line connecting the fuel control unit to the combustion chamber's injector wheel was partially obstructed by coke. This residue was identified as the carbonized remains of rubber or plastic.
Findings
- The engine failure was a flameout, resulting in a total loss of power.
- The investigation found that the fuel inlet union was clogged with black coke, which contained elements such as calcium, barium, and magnesium, suggesting the material originated from spent rubber or plastic rather than jet fuel.
- It is believed that a small piece of debris, such as an O-ring or seal fragment, entered the fuel system—potentially during assembly or installation—and eventually blocked the fuel flow to the injector wheel.
- The impact in the ditch caused a secondary fuel leak when the fuel line was punctured by a sharp object during the rollover.