Chinook - Still Hitting Back 3 (Merged)

[walter kennedy]

BOAC
re your post #4820 accusing me of making an error with the waypoint A coords:
I did caution you in post #4813 of 14th Jun thus:
<<If you just want to play with Google earth, you can put the cursor on the lat/long of the points of interest (don't forget to be careful about converting arcsecs into dec minutes and vice versa where required) and put a marker there which will stay on your computers presentation of Google Earth (so it's worth doing) - impact point, pos of wpt change, etc - see how it lines up. >>


BUT you still got them mixed up, didn't you? The original post you quoted (#3935 6Jan09 page 197 of this thread) had waypoints with decimal minutes of arc as opposed to arcseconds in Google Earth - .50' = 30” so
55:18:30” is the same position as 55:18.50'
fifty five degrees, 18 minutes and 30 seconds is equivalent
to fifty five degrees, 18 decimal five minutes.
No offence on this one, many get confused, you just need to practice on this case – I had hoped many more would have done so years ago – once we are all familiar in our minds with the geometry we can discuss the track issues – people are often shy of grasping the nav nettle as it is easy to make howlers and few want the embarrassment.
I did make a confusing error in post 4813 of 14th June – I had put in an extra zero (trying not to wear reading glasses when on computer) – I had meant the detailed 1 in 25 thou – not the 1 in 250 thou scale that no doubt rang a bell with you.
To save further delay and confusion, here are 4 points as corners in format that you put in Google Earth for that LZ:
55: 18: 34.00” 05: 48: 03.00”
55: 18: 32.00” 05: 48: 03.80”
55: 18: 33.60” 05: 48: 01.50”
55: 18: 32,30” 05: 48: 01.60”
I also suggest you put markers at the other points of interest, such as waypoint change and initial impact, if you use the ruler function to measure wpt change to impact and close the ruler without clearing the result you are left with a useful track line that remains whatever aspect you view the aerial pix from - well worth juggling around to get a feel - and, while this line is still there, do the flight simulator option: chug along at about 150kts to get a feel for how quickly the ground rises as you pass the LZ area - you would want to be sure of your actual closing range that close in if the ground detail was as fuzzy as in the pix..
If you go to a site called “Marinas” you can get a free download of a screensaver that is an excellent view of the area from light house to the LZ from about the elevation of the light house just off the coast – just look at the site with keyword “Mull” and there will be a few to look through, the one I mean should be obvious – it is high res so when you view it you can zoom in – worth a look.


You wrote: <<I am confused as to how you think they were using TANS - a reported change of waypoint off the coast would suggest a change from WPT A to B, so how do you explain this 'track' of 035 towards a WPT (A) which has just been bypassed? They would surely not STILL be navigating on WPT 'H' (home?) at this stage?>>
Even those most hostile to my views would surely acknowledge that I have made a lot of effort to explain the track, hdg changes etc in many detailed posts over many years – once again I am tempted to ask you to read the posts – very briefly here now, so that recent readers may grasp the basic idea and then hopefully go back over past detailed posts:
For starters, all compass references to magnetic north (at the time of the crash);
Aldergrove to the position of waypoint change – they had departed on 027 VOR radial (as they had declared they would to ATC) and had held 027 accurately (Boeing analysis) – if you stick to 027 (mag at the time) you go right to waypoint A from Aldergrove VOR);
they then dumped waypoint A from the SuperTANS and turned right (Boeing) - it was still ahead and useful when they dumped it – waypoint B was of no use to them where they dumped it as the track to it would have been over higher ground than that which they eventually struck (they would have had to have selected B several miles earlier to have allowed a simple change of track to it to keep them clear) ;
the track from waypoint change to the position of first impact was straight until last second evasive manoeuvre (Boeing) and this track was 035;
035 was the course selector setting as found on the handling pilot's Horiz Situation Indicator – it is also the obvious best line to the LZ;
they had started to slow down in air speed (Boeing analysis) with engine power matched but increased tailwind as they approached and crossed the shoreline masked this maintaining the ground speed;
RADALT warning set appropriately for imminent landing in marginal conditions and HP's baro alt set for landing at elevation of that LZ.
I have always held the view that this crew in particular would not have trusted the SuperTANS to be accurate and believe that their actions could be best explained by their having referred to some other radio nav reference that they believed intrinsically accurate and that was supposed to be at the LZ and so dumped waypoint A when it became apparent that there was a significant conflict between the two. I have suggested a candidate equipment that was fitted to several HC2 Chinooks a few months later – had the ground equipment (handheld) been ½ mile or so up the hill (rather than on the LZ) then the early turn and too fast/too close approach is explained – don't forget, they may not have been intending to fully land, perhaps just a close pass/turn over the LZ to demonstrate the usefulness of the equipment for pinpoint local nav (as it is so often used for).