Eurocopter has been confident for some days that the 23 August Sumburgh CHC Scotia Super Puma accident was not caused by a technical fault, but it was unable to go public on why.
Now the UK Air Accident Investigation Branch, having downloaded information from the cockpit voice and flight data recorder, has released a factual statement saying that so far they can see no detectable technical failures, but they are continuing their investigation in greater detail.
About a week ago the Aberdeen-based Helicopter Safety Steering Group lifted its voluntary grounding covering all Super Puma variants. The next day (30 August) the UK Civil Aviation Authority backed the HSSG’s position, stressing that it didn’t believe the accident “was caused by an airworthiness or technical problem, and considers that the decision by the operators to resume Super Puma flights is appropriate”. To say that in advance of the CVFDR download, they must have been pretty confident following interviews with the crew and surviving passengers that the aircraft was technically safe.
According to the data recorder, the crew intercepted their localiser/DME approach to runway 09 at the correct height on the extended centreline, but quickly descended below the ideal profile with the airspeed also reducing rapidly.
The engines were “producing power at impact”, says the statement. Maybe, but was it the power the crew were demanding? The AAIB’s statement is so terse one suspects they think it was.
But that’s just one of the questions still to be answered by more detailed study, in which the AAIB is now engaged. If it really was a purely human factors-centred accident, the Board has to find out why the crew was able to misjudge the approach as they did. Were they distracted? If so, by what?
The weather was pretty typical for Shetland, a thin mist with broken low cloud, 2,800m visibility. Out the front windscreen the crew would have seen a grey sea below, a grey mist ahead, and grey skies above, probably all merged. They would not have been able to see the runway lights at any point during their approach because they hit the water about 2,800m from the runway threshold.