Investigation Summary
Helikopter Service Flight 165 was a routine offshore transport mission that ended in catastrophe due to a critical component failure in the main rotor assembly. The investigation conducted by the Accident Investigation Board Norway (AIBN) determined that a fatigue crack had developed in one of the knuckle joints, which are vital components connecting the rotor blades to the rotor head. As the crack progressed, the joint eventually failed, leading to the loss of a main rotor blade. The resulting extreme imbalance and loss of lift made the aircraft uncontrollable, leading to a rapid descent and impact with the North Sea. The helicopter, which was two years old at the time, had logged approximately 10,000 flight hours, highlighting the danger of fatigue even in relatively new components.
Final Conclusions
The Accident Investigation Board Norway concluded that the primary cause of the accident was a fatigue crack in a knuckle joint. This structural failure led to the detachment of a main rotor blade, resulting in the total loss of aircraft control and the subsequent fatal crash.
Photographic Evidence (1)
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Systems & Failure Modes
Main Rotor Knuckle Joint
A mechanical component that connects the rotor blades to the main rotor hub; its failure due to fatigue caused a blade to detach.
Main Rotor Blade
The primary aerodynamic surface providing lift; the loss of one blade caused catastrophic imbalance and loss of control.
Interesting Facts
- 01The aircraft was a two-year-old Sikorsky S-61 manufactured in 1976.
- 02The helicopter had logged approximately 10,000 flight hours at the time of the crash.
- 03The accident resulted in the deaths of all 16 passengers and 2 crew members.
- 04The crash site was located at coordinates 61°01′N 002°48′E, approximately 55 nautical miles west of Sognefjord.
- 05The failure was traced to a fatigue crack in the knuckle joint of the main rotor.
Safety Actions & Advisories
Main Rotor Knuckle Joint Inspection
Source ↗Following the investigation, mandatory inspection intervals for the S-61 main rotor knuckle joints were revised to detect fatigue cracks before they reached critical length.