CRUISE CLIMB
This is one of the most significant aspects of this incident and I believe an important indicator of what the crew was doing.
It was established that the a/c had been in cruise climb in the latter part of its approach to the Mull – it was a rate of climb that used the excess power available without requiring the cruising speed to be reduced – that is, apart from increasing altitude, the a/c continued on the same route plan.
The AVMs cited it as an inappropriate rate of climb in the circumstances – as indeed it was to clear the high ground never mind achieve the minimum safe altitude HAD THEY BEEN INTENDING TO CROSS THAT HIGH GROUND. In fact, if they had been intending to cross the headland and did not want to slow down (therefore using cruise climb) they would have had to have selected it many miles before they did and therefore while they were evidently not having any problems (well before they changed waypoints on the SuperTans for example) and well outside the range of nav error even with the SuperTANS.
If you really want to keep up with the following argument you should get hold of the Ordnance Survey 1:50 000 for South Kintyre and draw on lines for the a/c hdg and waypoint A.
Let us assume for a moment that THEY WERE GOING TO TURN UP THE COAST (as did so many helicopters crossing there) – check where waypoint A is on the map (yep, right on the shore near the lighthouse). You can see it is not much of a turn to the left that they would have had to make and they could have continued along the shoreline quite happily halfway up between sea level and the cloud base – the mist very close by to the right but clear to the left, ahead and directly below. SO WHY CLIMB AT ALL?
Continuing with this simple assumption (turning left up the coast) and adding the assumption that nothing mechanical went wrong we are left with the conclusion that they simply started that turn too late – let us say, that for whatever reason at this stage of this argument, they thought that they were a bit further away – lets say ½ to 1 mile.
Note that the a/c’s line of approach to waypoint A can be projected to the aerodrome at Macrihanish.
Had they been maintaining that cruise climb from that bit further out, by the time that they reached the (actual geographical) position of waypoint A they could have been about 1000 ft – or, say, just below the cloud base. If you do a transection from waypoint A at that height you will notice that the highest ground is close to A such that they could have had (radio) line of site to the aerodrome and used the MAC TACAN (ie DME) – and the a/c’s TACAN CU was set appropriately for this (Ch 107).
BUT WHAT IS THE USE OF SUCH A FIX THAT THEY COULD ONLY HAVE GOT WHEN THEY GOT THERE? Well, obviously it would not have been a factor in getting them there, but supposing they were tasked to check out some other system deployed near waypoint A while they were passing – they may not have been able to see the ground team (the mist being on the ground just inshore) and so the evaluation would not have been a satisfactory exercise or they may have had some misgivings about the range to go (it was after all very close to high ground) – being in line (as near as makes no significant difference in range measurement) with the MAC TACAN/DME would have allowed a good comparison.