The UK AAIB has finally put out an initial bulletin on the happily non-fatal loss of the Bond Helicopters Eurocopter EC225 Super Puma in the North Sea last month. Most of it confirms the semi-official version of events which has been pretty well-circulated in the offshore helicopter community. But there's some very interesting additional information.
This CFIT accident, in which the aircraft flew fairly gently into the sea on final approach, incidentally involved a 17,200hr commander - with 198hr "on type".
Let me be clear here - the AAIB at this stage has produced a purely factual report and the points I'm making are my own. Do be sure to read the original. (I've also never piloted a helicopter and have only superficial knowledge of North Sea operations.)
Here's the new bit. On the transit out to the rig the aircraft was cruising at 5,500ft AMSL and received a terrain avoidance warning system (TAWS) "caution caption illuminate" which cleared after a few seconds. The AAIB says: "This caption (not recorded on the FDR) indicating there was a malfunction in the TAWS equipment."
The report relates how the crew later set the radio altimeter warning bug to a height of 150ft before the final approach. And it explains: "Descent below 150ft generates an audio voice warning of 'CHECK HEIGHT'. This warning can be suspended to prevent activation. A second audio voice height warning of 'ONE HUNDRED FEET', which cannot be suspended, is automatically activated by TAWS when descending through a height of 100ft radio altitude."
Now - jump to the end of the report - and there is this: "During a review of the recorded data from the accident flight no 'ONE HUNDRED FEET' audio voice warning was evident. This callout cannot be suspended and it was clearly audible in the recording of the landing at the end of the previous flight.
"Furthermore there was no evidence of a 'CHECK HEIGHT' callout, although the position of the switch which is used to suppress this function was not a recorded parameter. No warning parameters were triggered and no alerts were evident in the audio recordings."
So, we shall perhaps never know what the position of that switch was, but nevertheless there is the mystery of the missing ONE HUNDRED FEET' call-out.
I'm not qualified to comment on the precise importance of either of those call-outs and what their unexpected absence would mean to a North Sea crew. But I'm quite sure that their absence should significantly change one's view of this accident.
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