pulse1
<<Like some others on this thread you do have a tendency to ignore questions, and answers, which do not suit your particular arguments.>>
I would have thought that I have made my best efforts to answer all questions put despite lousy feedback and often misleading answers.
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<<May I therefore repeat a question which I asked you some time ago and which you ignored.
If a landing on the Mull was planned, why do you think that they changed the Tans waypoint to Coran just before they reached the lighthouse? >>
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I believe that I have thoroughly addressed this in numerous previous posts if you care to read through them I will nevertheless summarise here and now:
From data recovered at the known position of the crash, it was possible to make two significant conclusions as to the accuracy of the SuperTANS, which were:
1 The SuperTANS position at power down accurately reflected the actual crash position;
2 The accuracy of the Doppler component was sufficiently accurate to suggest that the a/c had not been manouvring much/had been on steady tracks for a significant period (briefly, if you are turning the Doppler system does not get a steady velocity component and this throws its algorithms out).
(This latter point reinforces the argument that they had been on a steady course and were surprised at their proximity to the ground in the last seconds.)
So the SuperTANS would have been an accurate aid which gives us two conclusions:
1 The position according to the SuperTANS for the waypoint change was accurate (and as can be seen from the maps I posted some time ago, this was very close in);
2 Their position relative to waypoint A would have been invaluable (as had been mentioned by one of the RAF witnesses at one of the inquiries who said in so many words that in changing it, they had thrown away their only accurate reference of use to them in their situation) so the question you ask is very relevant and I repeat my thoughts:
Although it had been accurate on the day, Flt LT Tapper was an acknowledged expert in nav systems and knew full well the limitations of the SuperTANS especially after a flight over water (the Doppler usually gets screwed up and this usually is dominant in the algorithms when mixing with the GPS data) in fact he had warned others in his outfit his concerns over this;
the bottom line is that he would not have trusted it to have been accurate to within ½ a mile or so after a sea crossing;
this has two consequences:
1 with no other (permanent) external radio navaid within range (other than the Mac NDB which would not have been of much use in their situation) there is no way he would have thought it prudent to have got anywhere near as close in as the position of waypoint change (up to and including which they surely had no control problems) relying upon the SuperTANS alone (the margin for possible error was greater than the distance to the shoreline);
2 The only thing an experienced pilot would trust to be relied upon in those circumstances and which would be taken as more accurate than SuperTANS would be a local DME system of some kind as they do when extracting personnel in exercises and operations, approaching a FAF in bad conditions, avoiding a local hazard near FAFs, etc, etc, relying so often on an ARS6/PRC112 combination.
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But still, as you so rightly ask, why drop waypoint A in the SuperTANS?
My only suggestions for this are:
1 The captain had decided that the SuperTANS was in disagreement with some other prefered reference and so no longer needed in the immediate locale and so it was moved on to the next waypoint to which they would be headed immediately after the completion of their immediate planned manouvre;
2 If ARS6 was being used and if data from it could have and was being used to drive the HP's HSI, perhaps such data and waypoint A data from the SuperTANS was too close to be unambigious (not much obvious difference) and so waypoint A was dropped so that the HP could not have inadvertently steered on it had his HSI been left selected to the SuperTANS.
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<<It just doesn't make any sense to me, especially in marginal weather and using an untested navaid as you suggest.>>
The marginal weather that I have gone to great lengths to describe in past posts that affected them was the local upslope mist that converged with the orographic cloud at about 800ft they were not lost in fog but the land ahead had its ground detail obscurred and the hill top topography was obscurred such that visual judgment of their distance off would have been seriously impaired they would not have approached at any sort of speed without some local, accurate reference for range as they did not have radar the only thing I can think of is a PRC112.
untested navaid ? - it is intrinsically accurate as a local DME and its interfaces with the a/c are by design simple as likely to interefere with other systems as plugging a GPS into your car's cigarette lighter (as I have described before).
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<< Surely, they would have used a Tans waypoint more appropriate for the landing site as a back up, either the field itself or an IP. >>
I have been to the site with a GPS and plotted on maps/charts the position of waypoint A it is the obvious (virtual) inner marker for the landing area (the green triangle that I have described in previous posts) the site used by Chinooks previously waypoint A is just off the cliff that is the threshold for that reasonably spacious, firm, level area of ground.
The landing pad at the lighthouse (the marked hardstanding) is too small for a Chinook.
You could not want for a better waypoint to put in your system if you were wanting to land on that green triangle Flt Lt Tapper had himself landed a helo at that site on at least one previous occasion it used to be used frequently for exercises by mil helos incl Chinooks.
Funny how no one on this site nor anyone in any of the inquiries (Oh!, apart from one of the AVMs who was quite specific about Chinooks landing there) had mentioned the relevance of waypoint A to a known landing area.
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I hope this answers your questions now how about some constructive feedback?
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Tiarna
Much of the software debate has centred on the FADEC I have made numerous posts pointing out that the engines were found to have been matched this is a condition achieved when in steady state for at least several seconds when either the FADEC has actively matched them or the pilot has himself matched them with his beep trim buttons it would be an unexpected state for a Chinook that was experiencing some sort of undemanded power surge or in a situation where the pilot was making emergency manouevres.
The Special Trials Fit (STF) issue cropped up from the clue of the work done on the anti-vibration mounts immediately before the final flight (a common consequence of STFs was initially incorrect anti-vib mounts being fitted) in no way do I expect that ARS6 equipment (had it been fitted), because of the simplistic interface requirements, had anything to do with any other avionics malfunction that may have contributed to this crash.
Such a system is intrinsically very accurate but, and this is the thrust of my argument that this aspect be thoroughly checked out, the handset on the ground being somewhere other than where the pilots expected it to be would explain everything that is known about this crash EVERYTHING.
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Ancient Aviator
There are others who have said privately that it was definitely on board but subsequently are loathe to put their heads up in the public forum no doubt they have had a flea in their ear.
Why anyone with information would hold back in these circumstances is beyond me what personal or group considerations outweigh the public good of examining whether a system was being used that could have been wilfully misled by a third party bearing in mind the people on board the implications for this in our country are just too profound.