Ark Royal
Thank you for your posting of 4th May it was refreshingly clear on the options that the pilots had; unless I am mistaken, you are affirming that the turn up the coast at low level was their intention as planning for IMC was not on.
On the issue of the use of navaids in VFR, however, I would like to restate my hypothesis:
I have been involved in many sea trials in the NW of Scotland over many years and am very familiar with typical weather conditions; further, I have done much precise coastal navigation off the SE of the Isle of Wight (running wreck diving trips) and on many occasions the prevailing wind formed localized mist as it rose over the landmass; on one such occasion I was coming into our most popular site which I fixed visually with transits; I could see the shoreline clearly and was not using Decca or radar to get to the approximate position to wait for the mist to clear for the transits; however I could not see familiar features that were higher up from the shoreline and when the mist momentarily cleared I was surprised at how (dangerously for the boat) close in I had got; subsequently, in those conditions I moved in using Decca and not the Mk1 eyeball and that is with the shoreline clearly visible at a very familiar location.
ZD576 was coming in very fast and was heavy;
If, say for operational reasons, it was desired to turn as close as possible to the land just clear above the ground hugging mist (as a helicopter actually did while I was talking to the lighthouse keeper in identical weather conditions) it must have been awfully tempting to use the TACAN for a convenient countdown (distance wise) to the starting point for the turn; they would have been approaching in clear air with the land mass clearly visible (and its shoreline) but with detail and features obscured by the ground hugging mist; you would not be comfortable heading towards that coast too closely in a boat at 20 kts never mind 150+; ZD576s TACAN CU was set accordingly.
I believe that I have put my view in an earlier posting that for strictly VFR waypoint A was already rather too close in (fixed by TANS) in those conditions and that it would have been risky to approach closer at their speed unless they were using something else. Dont forget that they had bothered to change the TANS waypoint just before A not something that would have concerned them if they had not been in control at that point. Further, this crew in particular had misgivings about the accuracy of the TANS they would not have relied upon it alone to get as close as waypoint A in those conditions either they got there and beyond visually or they were using the TACAN.
What is needed is for some pilots who regularly did this run to come forward if none read this thread, then someone who does could perhaps contact them.