TheAerosCo
RE your post #5271
There should have been radar data available from Lowther Hill which had both secondary and primary radar relayed back to ScotMil which could have been of great value in analysisng this crash – I have run a propagation model for an a/c at 500ft crossing from NI coast up to the Mull and got direct line of sight coverage right up to the Mull – further, I have given an example (years back) on this thread of contact with Lowther Hill radar for an Islander (air ambulance) that crashed into the sea a lot further away (to the west of Mac aerodrome) and arguably one would have thought that a broadside Chinook would have had just as big if not bigger radar cross section than an Islander – further again, I have referred to an article written by a reputable journalist soon after the crash; he was adamant that his source was in a position to know at ScotMil and that he said that he had seen recordings of the flight wherein it appeared that the a/c had been going straight in to the Mull; however, when I first brought up the question of radar on this thread it was in the context of what had been the squawk code as I thought it would have cleared up the question of the unusual squawk code found set – initially, I was ridiculed as it was said that Aldergrove had no secondary radar at the time and places like Tiree (?) were too far but no mention was made of Lowther Hill – when I did the research and brought up the article by the jounalist someone on this thread threw in the red herring that Prestwick Aerodrome would not have had the coverage, again without mentioning Lowther Hill; when I did the further research on the coverage of Lowther Hill the existence of recordings was flatly denied by people who said that they had either been there at the time or had looked at all relevent recordings and had seen nothing of ZD576.
Little wonder I do not accept many rebuttals at face value.
By the way, with reference to the Boeing analysis – I rather thought that Mitchell did point out assumptions and tried to estimate error windows – at any rate a useful framework to add one's own calculations to. The fundamentally important position where the waypoint was changed, as I recall from memory just now, was derived principally from the range and bearing to waypoint B that the SuperTANS had stored at the point of changing waypoint; so, the accuracy of the position of waypoint change is as accurate as the SuperTANS was at that point – after a sea crossing, the (Doppler/GPS nav computer) SuperTANS could be expected to have significant error but we do have a fixed point not that long after the position of waypoint change and that point was the impact position – retrospectively, it was deduced that the SuperTANS had been reasonably accurate in the latter stages of the flight – sadly, a retrospective that the pilots would not have had and so would have not viewed the SuperTANS as precise if it contradicted a local reference when closely approaching the Mull.
Regarding the rest of the reconstruction of the whole track, Mitchel's time/distance caculations had it (quite reasonably, I think) that the a/c could not have done much else other than to have made a bee line from Aldergrove to the position of waypoint change at the high cruising speed – makes it a lot easier? Aldergrove VOR 027 radial (at the time) would (extrapolated, of course, with the SuperTANS) have taken you exactly to the LZ that I have referred to – so to get there with the SuperTANS ('cause you wouldn't have had the VOR that far at their height) you would need a terminating waypoint there and if you read off your chart to nice roundy figures you get the coords that were waypoint A. It is reasonable to assume that their cruise speed (in terms of air speed) would have remained constant from the ATC fix to the position of waypoint change and so you can work backwards for that long leg using your best estimates for wind and see if it all fits together – as Mitchell did.