What happened
On 4 October 2005, a Hughes 369D helicopter, registration SE-HVY, was performing a commercial power line inspection flight in O county, Sweden. After completing the day's work, the pilot landed at a farm near Lundsbrunn to visit an acquaintance. Upon departing from a nearby grass field to continue the return flight to Skövde, the helicopter began a climbing turn toward the northwest.
As the aircraft reached a forward speed of approximately 30 knots at an altitude of only 5 to 10 meters, a loud bang was heard and the engine ceased functioning immediately. Due to the extremely low altitude and speed, the pilot was unable to establish an autorotation before the aircraft struck the ground. The helicopter impacted a field of loose soil and landed on its left side. While flames briefly emerged from the engine exhaust, the fire did not spread, and the pilot was able to exit the wreckage uninjured.
The investigation
The Swedish Accident Investigation Board (SHK) conducted a technical examination of the wreckage and the Rolls-Royce 250 C20B engine. The investigation focused on the sudden engine stoppage and the physical damage to the compressor section. Investigators performed a metallurgical analysis of the engine components, which revealed significant damage to the compressor blades and guide vanes.
Findings
Technical analysis determined that the engine failure was caused by a fatigue fracture of a compressor blade in the third stage. Microscopic examination revealed that this fatigue crack was initiated by corrosion at the root of the blade. The investigation noted that while the aircraft was maintained according to regulations, the compressor washing—a procedure intended to prevent such corrosion—was not documented in the primary maintenance logs. The presence of corrosion was a known risk for this engine type, particularly when operating in environments where salt or moisture might accumulate.
Safety action
To mitigate the risk of similar occurrences, the Swedish Civil Aviation Authority has recommended that operators of this engine type be formally notified of the risks associated with blade corrosion. Specifically, the recommendation emphasizes the necessity of strictly adhering to manufacturer guidelines regarding regular compressor washing to prevent the onset of fatigue-inducing corrosion.