Nesøya air accident

Cause and context

In the course of the accident investigation it was determined that the aircraft's nose had suddenly dropped on final approach, causing the Viscount to lose altitude rapidly. Because of the low altitude it could no longer be recovered from the vertical attitude.

The investigators could not settle on a cause of the accident and put forward two hypotheses:

Ice formation had occurred in flight in the area of the tail unit. The ice accretion caused the angle of attack at the horizontal tail to reach supercritical values. When the pilots extended the flaps to the final position for landing on approach to Oslo, the centre of lift shifted rearward. Loss of control and the crash followed.

Because of an incorrect propeller setting, the propellers generated a braking force that led to a loss of control.

Ultimately the investigators considered the second hypothesis to be slightly more likely than the first. From today's perspective, however, further incidents with the Vickers Viscount suggest the first hypothesis. For example, in connection with the crash of a Viscount on Linjeflyg Flight 618, which occurred under almost identical conditions, it was pointed out that the Vickers Viscount is particularly susceptible to icing of the horizontal tail and that under the climatic conditions in Northern Europe in winter this type of icing occurs quite often. Continental Airlines Flight 290 also had an almost identical accident sequence, which was likewise attributed to unnoticed icing of the horizontal tail.