A very detailed examination of the crash site and the wreckage of the aircraft was carried out by Mr Cable of the Air Accidents Investigation Branch of the Department of Transport. He subsequently prepared a report, the main text of which extends to 60 pages. He gave evidence during the inquiry over a period in excess of four days and spoke of the content of his report. This and his evidence speak for themselves and I do not think that there would be any useful purpose in my rehearsing them at length. I have incorporated some of the salient conclusions of his report in the findings in fact, and rather than attempt to summarise or paraphrase what else he had to say, I think that it would be preferable simply to quote those parts of his report which seem to me to have particular relevance to this inquiry (and for the avoidance of doubt I accept as accurate what is said in these excerpts). Mr Cable began his report with a summary which was as follows:

  "ZD576 impacted a hillside near the Mull of Kintyre Lighthouse while in transit from Aldergrove to Inverness with four crew and 25 passengers on board, There were no survivors. My examination of the crash site and detailed wreckage inspection and testing showed that the aircraft struck a rocky outcrop 810 feet amsl on the side of a 1,404 feet amsl hill while tracking 012ºT at around 150 knots groundspeed and climbing at approximately 20º. It was erect, banked slightly left and pitched around 30º nose up, probably with cockpit control demands of substantial aft and left cyclic stick, left yaw and full thrust present. A Boeing simulation indicated that a sharp up-collective and back-cyclic pull-up manoeuvre combined with initial conditions of approximately 150 knots airspeed and 1,000 ft/min climb rate was required to produce the assessed combination of aircraft pitch attitude, flight path, speed and DASH and LCTA extensions at impact. Much of the fuselage undersurface and rear end was torn off and the right and lower area of the cockpit damaged. The aircraft then travelled almost 200 metres airborne while sustaining fuselage strikes from rotor blades and executing extreme violent manoeuvres. It impacted the ground inverted and broke into two major pieces which tumbled a short distance, shedding the aft pylon and both engines. Fuel tanks on both sides ruptured at initial impact and extensive ground fire initiated, severely damaging much of the remains.

  The aircraft's completeness could not be positively verified but no evidence was found to suggest pre-impact separation of any part. Indications were found that both flight control hydraulic systems had been pressurised; thorough assessment of most control system components was possible and revealed no signs of pre-impact failure or malfunction, although the possibilities of pre-impact system jam or detachment of control pallet inserts were not positively dismissible. Available evidence indicated normal AFCS operation. The integrity of the aircraft's electrical generation system could not be positively established, but a number of services had been receiving power at impact; available evidence suggested that all electrical power had been lost very soon afterwards. 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. Both powerplants were operating, at similar, intermediate power levels that possibly reflected aircraft manoeuvre effects, and the surviving No 1 (sic) DECU monitoring system memory indicated that no anomalies had been detected during the last flight and no unusual faults or exceedances had been recorded over its life. No evidence of explosive effects or pre-impact fire was found.

  A detailed investigation of possibly relevant technical aspects of the accident was made. The pre-impact serviceability of the aircraft could not be positively verified but no evidence was found of malfunction that could have contributed to the accident, with the possible exception of a radar altimeter system fault".

  In a summary of his findings in regard to the aircraft's instrument. Mr Cable recorded that the course selectors on the Horizontal Situation Indicators "were probably at 028º and 035º for left and right indicators respectively, and the left indicator steer bar had probably been indicating 0.9 divisions left at the time of indicator deformation". He went on to describe two faults in the radar altimeter system, one of which would not have affected the performance of the system below 800 feet. The other was a receiver fault of which Mr Cable wrote: "The receiver fault, apparently predominantly the result of incorrect adjustment and positively present before the accident had the potential for causing incorrect height indication due to false lock-on, but a previous flight test result indicated that this was unlikely, provided the antenna environment for ZD576 was similar to that for the test. In circumstances where the terrain closure rate exceeded the system's track rate limit of approximately 90 ft/sec the fault also was likely to have increased somewhat the maximum over-reading indication error that would have built-up before lock was lost and re-acquisition occurred, probably to approximately 80 feet".

  In a summary of his findings in regard to the aircraft's flight control system Mr Cable recorded that: "Almost all parts of the mechanical systems for each of the four channels were identified, with no evidence of pre-impact failure or malfunction, although the possibility of control system jam could not be positively dismissed. The collective balance spring bracket that had previously detached from ZD576's thrust/yaw control pallet had detached, but so had most of the similar inserts and the method of attaching components to the pallets appeared less positive and more difficult to verify that would normally be expected for a flight control system application, and little evidence was available to eliminate the possibility of pre-impact detachment of any of the pallet components."

  The reference in this last passage to the collective balance spring bracket having previously detached from the thrust/yaw control pallet was a reference to an incident which had occurred on ZD576 on 10 May 1994. On the RAF message form about this incident it was recorded that whilst returning to RAF Odiham for a rotors running crew change the pilot had noticed that the collective movement seemed heavier than normal. The aircraft had been landed at Odiham. In consultation with the oncoming captain a further hover check had been made. The collective forces had proved unacceptable and the aircraft had been closed down and engineering advice sought. On investigation it had transpired that there had been a failure of the bonding of inserts into the pallet to which the bracket had been attached with the result that it had detached from the pallet. At the end of the form there was a note as follows: "Emphasise that whilst symptom is stiff collective control the main flight safety concern is the danger of a loose article within the flying control closet". There was also an indication that the cause of the detachment was "to be determined following technical investigation by Boeing Helicopters". Following the incident an instruction was recorded in the Supplementary Flight Servicing Register of ZD576 to the effect that during a before flight service of the aircraft the security to its attachment point of the collective balance spring bracket should be checked.

  A similar incident appears to have occurred in another Chinook MkII helicopter on 20 July 1995. The incident signal relating to this incident recorded that the aircraft had been landed for hook checks and that as control was passed from a student pilot to the captain a slight "kick" was felt in the cyclic pitch. On taking control the captain found that the cyclic would not remain in the neutral trimmed position unless physically held there. If pressure on the cyclic was relaxed it moved forward in excess of two inches and had to be pulled back against moderate pressure. The soundproofing was removed from the control closet and it was observed that the mounting bracket for the pitch balance spring had detached from the closet wall. The aircraft was closed down and engineering assistance was sought. It was ascertained that the cause of the incident was that moulded inserts from the pitch balance spring mounting bracket had debonded from the pitch and roll control pallet. The signal ended with some comments by the Station Commander at RAF Odiham as follows: "Previous incidents involving debonding mounts occurred last year but as yet I have not seen results of the investigation. It may be that we should be concerned over production and/or assembly of these panels using inserts for which we do not seem to have a reliable inspection technique".

  For the sake of completeness it should be recorded that K was asked some questions about the earlier of these two incidents as follows: "Q.—The first point I want to ascertain is that at the foot of the page where the note is that "Emphasise that whilst symptom is stiff collective control the main flight safety concern is the danger of a loose article within the flying control closet" and I think we saw elsewhere that this was a matter which had been referred to Boeing? A.—Yes. Q.—And we also know that following this the visual check was instituted? A.—Yes. Q.—Are you aware that in December of 1994 the Boeing response was that it did not in fact constitute a hazard to flight safety and that the visual check need no longer be carried out? A.—No, I did not. Q.—I think perhaps the initial view that was taken was that there might be a risk of perhaps a spring becoming detached and falling down and impeding controls. Does that seem fair? A.—Or any other part of the assembly had become detached, yes. Q.—And if it is discovered that in fact the way that these items were fitted together that that was not likely to happen, you are not really in a position to help us with that? A.—No." But no evidence was led at the inquiry to substantiate the suggestions which were put to K in this context. Mr Cable was asked about the possible effect of a detachment from one or other of the pallets in the control closet and said: "A.—Detachment that had caused a severe flight control difficulty I don't believe would be consistent with the evidence I received from the site and wreckage examination and the way in which the aircraft approached the initial impact basically. Q.—Can you elaborate on that? If I understand what you are saying, the evidence available to you suggested a certain flight to the point of impact and do you say that that is not the flight you would have expected had there been a detachment in this area or not? A.—Yes, I think that is one aspect. I mean, the other is that there were ear witnesses in the area who have not reported any of the sort of fluctuations I would have expected to be reported if the aircraft was in any flight control difficulties and thereby excluding some dramatic manoeuvre at some period before initial impact. I understand there is other evidence from examination of the navigation equipment on the aircraft that again does not suggest flight control system problems." H was also asked about the matter as follows: "Q.—Now, can I ask you to give the court your view of the likelihood in the first instance of there being a simultaneous or near simultaneous complete loss of control of both pitch and control channels? A.—Yes, this would be something we looked at extremely carefully using the evidence of both the AAIB Investigation and the history of the aircraft in terms of possible loose articles and also in consultation with the engineers at Odiham in terms of the possibilities of such an occurrence and it is my belief that the possibility of a single control jam is highly unlikely. The possibility of a dual roll and pitch at the same time is even less likely".

  Among the many items examined by Mr Cable were the aircraft's Differential Air Speed Hold and Longitudinal Cyclic Trim actuators. Of these he reported: "It was clear that the DASH extensions found did not correspond to a high speed level flight condition whereas the LCTA extensions did, and it appeared possible that the settings could reflect a dynamic aircraft manoeuvring situation at the point of impact. A study was therefore undertaken to assess the consistency of the settings and to define the possible manoeuvre . . . A Boeing study attempted to define the manoeuvre necessary to produce the initial impact conditions that had been derived from the technical investigation. The response of the aircraft to a series of postulated control inputs was predicted by mathematical modelling simulating the Chinook HC2's behaviour, from a range of initial steady flight conditions. For each case a predicted time history of flight path, airspeed, attitude and DASH and LCTA extension conditions resulting from combinations of large collective thrust and aft cyclic stick control inputs was produced and assessed for a simultaneous match of the parameters with ZD576's initial impact conditions. In some cases control inputs were modulated during the manoeuvre. Sample results of Boeings' assessment of a wide range of possible starting conditions and control inputs are given in Ref 19. This showed that close simultaneous matching of the predicted conditions with the criteria was possible in only a few cases, and was very difficult or impossible in all cases with an initial airspeed of 135 knots and below and/or an initial climb rate of 500 ft/min and below. A ready match was found where initial conditions combined an airspeed of 150 knots and a climb rate of 1,000 ft/min and large collective and aft cyclic control inputs were postulated. The results in the case (Ref 19, Case 12) providing the best correlation, which occurred 2.9 seconds after the initiation of the manoeuvre, included:

  In layman's terms what this simulation demonstrated was that, in order to have created the conditions found by Mr Cable in the course of his examination of the wreckage of the aircraft and the site of its initial impact, the aircraft would have had to have been climbing at 150 knots airspeed and at a rate of 1,000 feet per minute when the control inputs postulated were made 2.9 seconds before the initial impact. And the result of these control inputs was to bring about a cyclic flare over a distance of 812 feet during which the aircraft's nose pitched up to 31º from the horizontal, its angle of climb increased to 20º above the horizontal, it gained 120 feet in height and its airspeed dropped from 150 to 135 knots.

  Mr Cable also spoke to a very detailed report prepared by Racal Avionics Limited on the aircraft's SuperTANS navigation system. This was recovered from the wreckage and the contents of its memory extracted for analysis of relevant data. Again, I do not think that it is necessary to rehearse everything that emerged from the analysis. But a number of points are worthy of mention. The GPS and Doppler positions recorded at powerdown were respectively about 200 metres to the south-west and to the south-east of the aircraft's initial impact point. The report narrates (paragraph 2.4.3.5): "The accuracy of a Doppler maintained position is very dependent on a good heading source. During manoeuvres when the heading changes, this will usually induce errors in a Doppler derived position, often due to the lag in the compass, but also due to latency associated with differences in the times at which all the many contributing parameters are input to the Navigation computer. The accuracy of the Doppler position over the flight suggests that there had been little change of heading throughout the flight". The calculated times at power off were 1659:10.4 GMT and 1659:36.0 UTC, in each case plus or minus half a second. The difference between the two was accounted for by the fact that the initial setting of GMT would have been entered by the crew of ZD576. The SuperTANS had been selected to GPS and the display at the time of power loss was as follows:

`^Tac:B'
`< < 025ºM'
`Dis:86.7Nm'
`vTTG:32.0'

  This indicated that the SuperTANS was being operated in the "Tactical Steer" mode and that a waypoint B would have been selected manually by the crew. The course to steer to the waypoint was 025oM and the two chevrons indicated that the aircraft should turn left between 10o and 15o to make good the required heading. The distance to the waypoint was 86.7 nautical miles with an estimated time to go of 32 minutes given the current airspeed of the aircraft and wind conditions. There was provision for the operation of a steer meter on the Attitude Indicators on the aircraft's instrument panels. The drive to the steer meter indicated a command to make a track change to the left by 14o but it is not known if this signal was being directed to the Attitude Indicators. The aircraft's true heading corrected for magnetic variation was 034.4oT, the true airspeed 127.6 knots, the system wind 30 knots from 170o, the system groundspeed 151 knots, the system track 026oT and the system drift west 8o. The baro-compensated altitude at power down was 665 plus or minus 50 feet. This did not coincide with the initial impact height of 810 feet. But it appears that the error may have been attributable to pressure changes at the time of the crash. The baro-compensated altitude 15 to 18 seconds before power down was 468 plus or minus 50 feet. There was no information within the SuperTANS on the aircraft's rate of climb.

  Five waypoints had been entered into the SuperTANS as follows:

  Waypoint A was evidently intended to be the Mull of Kintyre lighthouse. The latitude and longitude entered into the SuperTANS for the position of the lighthouse placed it 280 metres to the south east of its true position. The selection to waypoint B was made when the aircraft was about 0.81nm from the position entered for waypoint A on a bearing of 018ºT. At that point in time the aircraft was about 0.95nm from the position at power down on a bearing of 022ºT. No time is recorded when the change to select waypoint B was made.