This first appeared as a Comment in the 29 October issue of Flight International
The probe into August’s helicopter crash off Sumburgh, Scotland, is far from complete, but investigators are confident that, when the aircraft hit the water on short final approach, it had entered a vortex ring state.
With less than 200ft (60m) height to sacrifice in a recovery manoeuvre, the crew was powerless to halt the descent, with disastrous consequences.
There is insufficient space here to describe the complex aerodynamics associated with the vortex ring state, but they are fully understood, and so are the circumstances that lead to it.
A low and reducing indicated airspeed combined with a higher rate of descent than normal for an approach is key. So crucial to the investigation is discovering why the crew allowed this situation to develop without, seemingly, noticing. More than that, especially given recent commitments to examine North Sea safety, investigators need to determine whether this is a one-off, or a more persistent problem of complacency.
A few years ago, EASA’s European Helicopter Safety Team published a guide for rotary-wing pilots detailing how to deal with four of the industry’s greatest known and understood risks. They can all be avoided, but the most effective defence against them is pilot knowledge and constant risk awareness.
The Sumburgh accident seems proof that these preventative measures need further reiteration.