Investigation Summary
The accident occurred during the second sightseeing flight of the day for the Høstsprell festival. Approximately five minutes after departure, the helicopter was performing maneuvers at low level. The NSIA found that the aircraft was heavily loaded and its speed was increasing during a descent and right-hand turn. These conditions likely caused the flight control hydraulic system to reach its limit, triggering a phenomenon known as servo transparency. This resulted in a sudden increase in the force required to move the flight controls, effectively locking them or making them difficult to manipulate for the pilot. Because the helicopter was at a low altitude, the pilot had insufficient time and space to recognize the condition and perform the necessary recovery maneuvers. Although the impact was not considered a high-energy event, the helicopter was not equipped with a crash-resistant fuel system (CRFS). The fuel tank, which was 90% full, ruptured and ignited immediately, leading to an intense fire that consumed the wreckage and killed all six occupants.
Final Conclusions
The NSIA published its final report (2022/02) in March 2022. The investigation concluded that the loss of control was probably due to servo transparency, a known limitation of the AS350 type when operated at high speeds and high gross weights during aggressive maneuvering. The report emphasized that the fatalities were primarily due to the post-crash fire, noting that the occupants could have survived the initial impact if the helicopter had been equipped with a crash-resistant fuel system (CRFS).
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Systems & Failure Modes
Servo Transparency
Also known as hydraulic jack stall, this occurs when the aerodynamic forces on the rotor blades exceed the opposing force provided by the hydraulic servos, causing the controls to feel stiff or move in a direction contrary to pilot input.
Crash-Resistant Fuel System (CRFS)
A system designed to prevent fuel spillage and subsequent fire during a survivable impact, typically using flexible bladders and breakaway valves.
Interesting Facts
- 01The helicopter had logged only 73 flight hours since delivery.
- 02The aircraft was not equipped with a crash-resistant fuel system (CRFS), which was not mandatory for this type certification at the time.
- 03Ten out of eleven missing bolts from the engine-to-gearbox connection were eventually recovered during the investigation.
- 04The flight recorder was a small data storage unit not protected to the same standards as commercial airliner 'black boxes'.
- 05Weather conditions at the time of the accident were reported as good VMC (Visual Meteorological Conditions).
Safety Actions & Advisories
CRFS Mandate
The NSIA recommended that EASA require all helicopters delivered or imported to Europe to be equipped with crash-resistant fuel systems regardless of certification date.
Regulatory Progress on CRFS
Following the accident, EASA issued a Notice of Proposed Amendment in 2022 to mandate CRFS on older helicopter designs still in production. In 2024, EU airworthiness certificates were amended to mandate CRFS on helicopters.
Servo Transparency Warning
The NSIA recommended that Airbus Helicopters develop a technical solution to provide advance warning of or prevent servo transparency.
Training Enhancements
Recommendations were made to EASA and the CAA Norway to ensure AS350 simulator training includes early recognition and recovery from servo transparency.