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I have been recommending for years (on this thread) that this document is a useful framework to use for your own dist/time calculations.
You should bear in mind that on a flight earlier in the day, ZD576 was reported to have flown smoothly in excess of 140 kts TAS – more than an HC1 but as expected for an HC2.
However, without exceeding the optimum top end cruising speed, this was insufficient to have allowed anything other than sticking closely to the declared track of 027 mag from NI to the position of waypoint change – which helps in understanding (or rather reducing) the possibilities, and we are left with the simple conclusion that they had maintained a straight track of 027 at a constant airspeed for the whole of that long first leg (taking into account the wind) – there simply was not time for them to have slowed down and then speeded up at any point without significantly exceeding recommended max speed.
From waypoint change to the crash site, allowing for the significantly higher wind speed near and on the slopes of the Mull, they actually had dropped in TAS and this is consistent with the matched intermediate power level that was determined from crash investigations.
I have it that their turn was greater than Mitchel's estimate (I will expand on the analysis which gave this soon when I have time) – I had it that they had turned to 035 mag at or very near waypoint change which was as per the HP's HoSI course selector (suggesting an intended heading) and, as I recall, did not Racal's report state that at last steering command calculation (over land and very near to crash site) the STANS thought it was on a track of 035 mag?
I say that 035 mag was the optimum approach to a known LZ at waypoint A – why?: well from familiarisation with the site and talking to locals (incl a light house keeper) I found out that helicopters approaching that site lined up on a big rock in the sea just off the shoreline - a line of 035 mag (at the time) which was also the long axis of the spacious LZ. That LZ was at a height similar to the lighthouse and one of the baro altimeters was set as per QFE at that elevation, as I have explained in detail on this thread a long time ago.
Just on the above points alone, common sense has it that one obvious option (worthy of consideration at least) for their actions is that they had reached a point close in to the Mull (waypoint change) where they abandoned STANS navigation and turned in towards the land thinking they were lined up with that LZ (that they had visited on previous occasions) using some local reference and that they had eased up to coast in thinking they had further to go than they actually had.
With the conditions ahead on the landmass (oro cloud obscuring the higher topographical features and mist running up the slopes obscuring ground detail) they could only have attempted this by referring to something that they could trust – they only candidate for this would have been the CPLS and all that was required for them to have been misled as to their alignment and distance to go would have been for the PRC112 handset (associated with the CPLS) that should have been at the LZ to have been ½ mile or so up the slope from that LZ.
One of the primary uses of the CPLS is all weather approaches to LZs.
Despite this obvious possibility, this system was never mentioned at any of the inquiries to date yet we now know that it was fitted.
This alone is grounds for a new inquiry.