walter kennedy
10th Jun 2014, 16:26
MOK Chinook 20 yrs on
In all this time there has been little free and open discussion as to the navigation detail – perhaps it was that nothing further should be brought to light that could prejudice the objective of clearing the pilots’ names.
Well, you have passed that point now and operations in that area should have changed enough by now to avoid being compromised by some more consideration of what they were doing near the Mull – specifically the last 20s of the flight – after all, the conclusions of the Philip inquiry were rather open.
I will kick things off with a summary of the analysis that shows that they were in control and making good an intended track that had nothing to do with route nav but made sense for a common local activity:
they had made a bee line the whole way across towards a waypoint on the Mull but only about half a mile short they changed that waypoint in the nav computer to one 80 miles away;
they did not turn left as would have been desirable for getting on with their route but turned right a substantial amount;
the handling pilot would have had the desired track on his HSI course selector to steer by and this found to be consistent with a straight line from the position that the waypoint was changed to the point of initial impact, indicating an immediate and intentional right turn on changing waypoint;
further, to have maintained that track over ground, they would have had to steer into the wind a significant amount (7 deg) – it happened that both pilots’ HSIs’ compass cards were jammed at first impact at the same bearing and this was 7 deg right (into the wind) of the course selector setting, which was the desired track over the surface and which was made good all the way to the position of first impact – this shows effort in keeping to a particular track;
this makes any suggestion of control problems irrational;
the explanation of the significance of that heading is as follows: in 1996 I stood overlooking the site with one of the lighthouse keepers when a helicopter approached from seaward and swung around the lighthouse in a large arc; he indicated the alignment between the “green triangle” (a level area used, according to locals, as a landing spot in the past and by which was waypoint A that had been in the nav computer until changed before the right turn) and a large prominent rock just out to sea; he said that they “always” turned there when approaching the lighthouse; the alignment of that rock and the “green triangle”/waypoint A is the same as the track that they had selected and made good; later I superimposed the turning arcs of a Chinook at cruise speedat 30 and 60 deg angles of bank on a digitised map, starting on the bearing that was the track that they made good and it turns out that this was the ideal line up for starting a manoeuvre to swing around the lighthouse (as though it was the axis), well clear of the high ground, provided that they commenced the turn as they reached the rock, “green triangle”, or waypoint A – even if they missed such a crossing point the topography was such that they would still have been safe making the turn providing that it was initiated immediately that they crossed the shoreline, left or right of the exact aiming point;
the shoreline should have been visible (in the local conditions that day at that level) to MALM Forbes had he been at his window seat – had he been at this position and lost sight of the sea, say due to mist or crossing onto land, they should not have persisted with their intended approach – but he was found to not have been at the window seat but on the jump seat behind the pilots; the handling pilot would have been concentrating on flying the craft and on keeping it on course as directed by the navigator (and possibly equally by MALM Forbes) as there were no visual aiming points ahead; waypoint A was no longer selected in the nav computer and in any case the STANS back then would not/should not have been relied upon; Flt Lt Tapper and MALM Forbes must have been relying upon some other reference;
if for whatever reason the use of that reference misled them and they overran the land, with no clear visual cues ahead, they could have become (in a psychological sense) spatially disoriented – in the experience of both civil and military aviation there is a significant reaction time from the onset/realisation of being disoriented to getting re-orientated again and/or taking the appropriate action, and this has been found to be from 8 to 18 seconds – from crossing the shoreline where they did to initial impact was about 9secs.
In all this time there has been little free and open discussion as to the navigation detail – perhaps it was that nothing further should be brought to light that could prejudice the objective of clearing the pilots’ names.
Well, you have passed that point now and operations in that area should have changed enough by now to avoid being compromised by some more consideration of what they were doing near the Mull – specifically the last 20s of the flight – after all, the conclusions of the Philip inquiry were rather open.
I will kick things off with a summary of the analysis that shows that they were in control and making good an intended track that had nothing to do with route nav but made sense for a common local activity:
they had made a bee line the whole way across towards a waypoint on the Mull but only about half a mile short they changed that waypoint in the nav computer to one 80 miles away;
they did not turn left as would have been desirable for getting on with their route but turned right a substantial amount;
the handling pilot would have had the desired track on his HSI course selector to steer by and this found to be consistent with a straight line from the position that the waypoint was changed to the point of initial impact, indicating an immediate and intentional right turn on changing waypoint;
further, to have maintained that track over ground, they would have had to steer into the wind a significant amount (7 deg) – it happened that both pilots’ HSIs’ compass cards were jammed at first impact at the same bearing and this was 7 deg right (into the wind) of the course selector setting, which was the desired track over the surface and which was made good all the way to the position of first impact – this shows effort in keeping to a particular track;
this makes any suggestion of control problems irrational;
the explanation of the significance of that heading is as follows: in 1996 I stood overlooking the site with one of the lighthouse keepers when a helicopter approached from seaward and swung around the lighthouse in a large arc; he indicated the alignment between the “green triangle” (a level area used, according to locals, as a landing spot in the past and by which was waypoint A that had been in the nav computer until changed before the right turn) and a large prominent rock just out to sea; he said that they “always” turned there when approaching the lighthouse; the alignment of that rock and the “green triangle”/waypoint A is the same as the track that they had selected and made good; later I superimposed the turning arcs of a Chinook at cruise speedat 30 and 60 deg angles of bank on a digitised map, starting on the bearing that was the track that they made good and it turns out that this was the ideal line up for starting a manoeuvre to swing around the lighthouse (as though it was the axis), well clear of the high ground, provided that they commenced the turn as they reached the rock, “green triangle”, or waypoint A – even if they missed such a crossing point the topography was such that they would still have been safe making the turn providing that it was initiated immediately that they crossed the shoreline, left or right of the exact aiming point;
the shoreline should have been visible (in the local conditions that day at that level) to MALM Forbes had he been at his window seat – had he been at this position and lost sight of the sea, say due to mist or crossing onto land, they should not have persisted with their intended approach – but he was found to not have been at the window seat but on the jump seat behind the pilots; the handling pilot would have been concentrating on flying the craft and on keeping it on course as directed by the navigator (and possibly equally by MALM Forbes) as there were no visual aiming points ahead; waypoint A was no longer selected in the nav computer and in any case the STANS back then would not/should not have been relied upon; Flt Lt Tapper and MALM Forbes must have been relying upon some other reference;
if for whatever reason the use of that reference misled them and they overran the land, with no clear visual cues ahead, they could have become (in a psychological sense) spatially disoriented – in the experience of both civil and military aviation there is a significant reaction time from the onset/realisation of being disoriented to getting re-orientated again and/or taking the appropriate action, and this has been found to be from 8 to 18 seconds – from crossing the shoreline where they did to initial impact was about 9secs.