The aircraft was en route from Brønnøysund Airport, Brønnøy to Norne, an offshore Floating production storage and offloading vessel (FPSO).

At 06:00 a.m. local time (UTC+2), Helikopter Service Flight 451 took off from Brønnøysund Airport with two pilots and ten passengers, heading for the Statoil operated FPSO Norne.

The splined sleeve disintegrated, severing the high-speed shaft, which led to an overspeed of the right-hand power turbine which in turn burst, destroying the left-hand engine as well as to cutting control rods which made the helicopter uncontrollable.

[2] The crew could not be expected to have been sufficiently knowledgeable about the aircraft's control system to understand the seriousness of the intermittent overspeed alarm, and there were no procedures or checklists available that covered this scenario.

[2] The AIBN also found reason to believe that one of the HUMS accelerometers installed in the aircraft would have been able to alert maintenance crew about the change in vibration patterns in time to avoid the accident had it been serviceable since it was configured with a setpoint value.