Chinook - Still Hitting Back 3 (Merged)

[walter kennedy]

Cazatou
What a disgraceful way to try and obfuscate a new poster – you yourself posted on the issue of baro alts and so why would he have to go through all the other stuff to get an answer?
My experience at the FAI told me what to expect from the authorities ...
So Caz and Jayteeto I would like to refresh your memories with the information and my interpretation of it below (Jayteeto – it was the RADALT ALARMS that were of interest):
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The QNH at that time at Aldergrove aerodrome was 998,
The QNH at that time at Campbeltown aerodrome was 998,
The regional QNH (used by all aircraft in the area for route flying – briefly so they all have the same reference for altitude rel to each other, ATC info, etc) forecast was given by Aldergrove ATC to ZD576 as follows:
“The Belfast regional QNH from sixteen to seventeen hundred is niner niner one, changing on the hour niner niner zero and the Portree regional QNH sixteen to seventeen hundred niner niner one changing to niner niner zero”.
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The AAIB Investigation/Racal Report gives:
<<… Barometric altimeter subscale settings were probably at 989 and 991.5 mb. Several defects in the radar altimeter system were identified but had probably not severely degraded its performance and signs suggested generally correct indication at impact; low level warning cursors were at 850 feet and 69 feet, the selection of the audio warning could not be established>>
The “probably” indicating a high degree of confidence that the settings found in the wreckage had been set at these values before the crash.
Obviously the 991.5 makes sense as the regional QNH setting and thus increases confidence that both settings as found were as before the crash.
The 989 setting is a significant indication of their immediate intentions as explained below.
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The elevation of the base of the lighthouse is taken here as the elevation of the meteorological equipment located there at ground level according to the Met Office – this is 82m or 267ft. The lighthouse landing pad is right there and the“green triangle” landing area (that I have described in many previous posts) is nearby (waypoint A is 280m to the SE) on the same local area of flat ground – let us say roundly, 270ft ASL.
[Using the approximation of 1 millibar for 30 ft altitude change.]
For a QFE (a subscale setting that gives a reading of zero at ground level) to use for landing at that landing area at 270ft el, one would use the nearest suitable local QNH (from Met Office archives, RAF Macrihanish QNH at the time was 998) and compensate for its altitude by reducing the figure by 270/30 = 9 millibar to give an altimeter subscale setting of 989.
This is what was found set on one of the altimeter subscales.
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The suggestion by the BOI that the subscale setting of 989 could have been the Aldergrove QFE without equal consideration of the lighthouse landing pad nor the “green triangle” landing area (used previously by mil helos incl Chinooks) is misleading for the following reasons:
While the QFE for Aldergrove could have been 989 (at an elevation of 268 ft and with its local QNH of 998), they left with good visibility around the aerodrome and so would not have needed a QFE setting and indeed ATC informed them of the Aldergrove QNH which should imply a directive to use that setting;
It was 40 miles behind them;
They had crossed the Antrim hills with their track over a substantial area of ground in the region of 1000 ft ASL and with peaks nearby to 1500 ft;
There is a requirement that, if you are flying below Transition Altitude, regional QNH MUST be set unless approaching for a landing – that is to say, at the time of the flight, they should have had 991 set on BOTH subscales unless they were imminently landing at (or passing close to) a specific location.
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The Rad alt warnings set support the idea that they were attempting to land – an experienced pilot has given this description:
”The Rad Alt warnings were not set in accordance with the SOP. One was set above cruising altitude and the other at minimum* where it would have given little, if any, warning of impact with the ground. Again there was no indication that these settings had been altered by the impact.”
*The lower Rad Alt warning was set at 69 ft – this would only make sense if they were imminently intending to use the Rad Alt for touching down in bad local visibility.
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tiarna
The system as described too me when fitted to the HC2 Chinooks seems to have been “stand alone” - however, without a fully detailed technical desciption of the fit I do not know if there was any feed to the HSIs – manufacturers of the on board equipment have supplied diagrams showing the route of data to HSIs which is a normal and common fit – easy where there is a CDU and BUS architecture (eg 1553) that supports interfacing with inputs from several navaids as was the case in even the first HC2 Chinooks (eg HSI can select the nav aid to work from via the mode selector panels – typically either pilot can have his own HSI course selector working off the Doppler/GPS nav computer [SuperTANS in this case] or say a TACAN) and it makes sense to have the handling pilot's course selector working off a feed from such an interrogator as the ARS6 as they close in with the target – but perhaps the MOD preferred the captain having to relay the info to the handling pilot rather than have the trivial addition – do they still use speaking tubes?
Had the common practice of feeding the CDU with the data from the ARS6 (or whatever it is called in the RAF – we havn't even got that clear yet) been the case then the handling pilot's (HP's) course selector being set on 035 is apparent – from the position of waypoint change to the crash site was 035 mag (at the time) which would strongly suggest that the ground handset (PRC112 that such interrogators work off) was on that bearing from the position of waypoint change (someone on the ground with it who should have been at the landing area but who was ½ a mile or so up the hill for whatever reason explains all thet is known about this crash).
If the captain was verbally guiding him, it could only have been that the HP had selected 035 as an aide memoire for the course to follow – hardly worth it at such short range.
But alas unless some have the balls to come forward describing the actual configuration in HC2 Chinooks when they actually had then (which they did at some time) such discussions can't get anywhere.