bastOn
<<If you have no TANS or whatever what nav aids would you use? I look forward to learning your magic system! >> I hope the following post helps!
BOAC #5015
<<(unless, of course, you are on WK's side of a precision IMC approach to a hillside LDZ?) >>
Why the big leap from a VFR flight using a point reference for range from a limited area LZ? – even in clear weather, TACANs are used by helos approaching oil rigs and frigate heli decks as it is better to approach smartly, flaring out right on the pad to make use of the ground effect “cushion” rather than dither about, trying to get onto an elevated perch (drop offs on 3 sides), risking vortex ring starting - I gave an example some time back regarding the Australian Blackhawk that crashed on the deck of a frigate in clear, calm weather – the captain (the handling pilot in that case) ignored the copilot's warnings that, with reference to the TACAN, they were too close too fast – the captain insisted he could do it visually and got it wrong with fatal results. Imagine the converse, where the instrument is misleading you as opposed to warning you - no chance:
you are approaching a limited area with a precipitous drop off in front of it with all sorts of wind effects on a blustery day;
so you want to do a typical fast approach, smoothly slowing down but only getting down to that final flare right on the site so your rotors are cutting into clean air right until the ground effect can be counted on – accurate range judgment is critical and ZD576 did not have a radar;
the hillside beyond is fuzzy with streaking mist and the higher topography is completely obscurred – it would not at all be suitable for such an approach without the one system that helo pilots trust to be intrinsically accurate, and that is a local DME of some kind – and that is what a PRC112 is excellent as;
SF helos use this equipment all the time in all sorts of conditions for extractions and resupply – it is very useful for, say, getting to an OP and extracting a SF observer in a hurry and so, I would suggest, a demonstration of this capability would have been of interest to many of the team on board, not just a useful exercise for the crew, and therefore an exercise easy to sell to them.
The CPLS working off a PRC112 also gives approximate bearing (only to +/- 4deg using its inbuilt* UHF antennas as a DF) which could explain their turning right at the position of waypoint change (they turned onto 035 mag, judging by the track on this last leg, at this point, which went to the crash site, as was found on the handling pilot's Hor Sit Ind) – this is the long axis of that LZ and therefore the preferred approach line – referring to the annotated maps I posted some time ago, the geometry fits with a PRC112 that should have been at the LZ being ˝ mile or so further up the hill which of course also explains their approaching the LZ too close too fast.
Note* The on board equipment as supplied by the manufacturers for RAF HC2 Chinooks was self contained on a pallette with minimal interface requirements so that it could be easily transferred between such Chinooks.
Dalek #5009
<< … First of all remember, we are discussing a scenario. A possible sequence of events.
In the scenario I painted, the one time that JT would have known an almost exact Vis was, on departure at Aldergrove. He was very familiar with the local landmarks.>> - as indeed he was with the LZ at the Mull having landed there himself on at least one previous occasion, and would have been aware of the difficulties of distance judgment when approaching it in even clear weather due to the ground features and topography (at their angle of approach, they were far from directly approaching the light house as I have explaqined previously)..
<<If he assessed his initial Vis as our (theoretical) 3nms, he would, without further outside influences, expect to see the cliffs at 3nms. When the TANS told him the range was 3nms he would believe it because he "knew" it was right.>> But, as I have tried to explain over so many years, Flt Lt Tapper would not have trusted the STANS to keep him clear of the fuzzy ground as close in as the position of waypoint change which was at that point only a few hundred yards off to their right front (look at the annotated map).
<<I use only the TANS in the scenario, because I have never seen any evidence of any "on land" equipment being invoved.
If it was you will never get anyone to admit it. >> That is the trouble – but I have been hoping to shame some to come forward by posting my view that the ramifications have been far more serious than a bit of embarrassment to the RAF – and it is becoming increasingly obvious that the only reasonable explanation for their actions is that they were relying upon such equipment and so the longer it is denied the worse the RAF as a body will appear when it does come out. Some degree of “damage control” could be achieved by opening up on the exercise and pointing out the individuals responsible for suggesting it and putting it together.