We Really Will Never Know!
As someone who uses his own name I try to avoid getting involved in some of the less than helpful comments that sometimes appear on this thread, but I have to say I am both amazed and appalled by Courtney's last comment.
There are literally thousands of words, based on facts such as the AAIB Report which leave a doubt as to the serviceability of ZD 576 on that fateful day - there are just as many casting doubts on the introduction to service procedures and airworthiness standard achieved with the Chinook Mk 2 fleet at that time. How Courtney can "state", with such apparent certainty, that they "flew a fully serviceable aircraft" into the cliff, when even the Air Marshals accept that they do not know this, is remarkable, and I would certainly welcome his analysis of how he comes to this conclusion - please PM me if you feel it is more appropriate.
In the meantime, and with apologies for again taking up more space with some repetiton can I remind Courtney and others what the HofL actually said in their Part 6 conclusions:
166. If however the finding of negligence at or before the way point change has not been established to the required standard of proof, as we consider to be the case, this proposition does not stand up. The evidence before us was entirely consistent with an intention to alter course and fly VFR to Corran and equally inconsistent with an intention to continue on the same course over the Mull under IFR.
167. The AAIB were not able to exclude the possibility of a control jam given the level of system damage. Nor could they exclude the possibility of pre-impact detachment of the thrust balance spring attachment bracket and other inserts. It will be remembered that this bracket had some three weeks previously detached from the aircraft's thrust/yaw control pallet (see above, para 56). The AAIB were unable to assess the functionality of number 1 DECU owing to gross fire damage. Metallic contamination of the hydraulic system of the integrated lower control actuators found by the AAIB was thought to have been present pre-impact but not to have contributed to the accident; however, the subsequent experience of the US Army and their recommendations (see para 104 above) suggest that such contamination could cause disturbance in the normal operation of those components at the time. DASH runaways have caused temporary loss of control problems as Squadron Leader Burke explained, and UFCMs and false engine failure captions have also afflicted Chinook Mk 2s. Mr Cable accepted that it was possible that there had been an intermittent engine fault which had subsequently reverted to normal before the impact. The problems arising from the newly installed FADEC system had not all been resolved by June 1994; and the Boeing simulation has been shown to have relied to some extent on postulations which are impossible in performance and parameters some of which do not fit with what was found by the AAIB. Can it in these circumstances be said that there is absolutely no doubt whatsoever that it was the voluntary action of the aircrew - including not only both pilots but also MALM Forbes who in our view was probably assisting with the navigation - which caused the aircraft to fly into the hill?
168. Squadron Leader Burke, when asked whether he saw anything significant in the position of the rudder pedals which were at 77 per cent of full travel, replied that it was "an enormous rudder input", unthinkable at high speed (Q 719; see above, para 112). He had also referred to this matter through one of the papers which he had submitted to the Committee in the following terms: "The position of the rudder pedals on impact (almost full left rudder), the high impact speed, and the fully up, or close to fully up, lever position coupled with 100.5% NR[39] and only 70% torque suggest that an erratic flight path typical of a partial control loss is the most likely of the many guesses as to what was happening in the cloud on ZD 576's last seconds of flight".
169. Witness A commented, "There is absolutely no reason for applying that amount of yaw pedal during forward flight and the only reason I can think of for applying that much yaw pedal would be if the aircraft was becoming extremely difficult to control" (Q 807). He went on to state that the view of the Board that the pedals had been displaced by impact could not be ignored either.
170. Squadron Leader Burke expressed the view that the most likely cause of the accident was a jam of some kind affecting the control of the aircraft, perhaps arising from displaced articles in the broom cupboard (Q 738). A UFCM resulting possibly from a DASH runaway and causing temporary loss of control was also considered by him to be a possibility (Q 739). Such a runaway could cause a temporary increase in rotor speed which the pilot would seek to contain by raising the collective lever thereby forcing the aircraft to climb perhaps unexpectedly into cloud.
171. Witness A considered a control jam to be a strong possibility for the cause of the accident but certainly not an exclusive one (Q 806). He also cited the possibility that a control problem in pitch could have produced oscillations which resulted in the 30 degrees pitch up position in which the aircraft was found (Q 844). Mr Perks expressed the view in his second memorandum that a major mechanical flight controls failure could be an explanation for the difficulty which Boeing experienced in matching their simulation to the data provided.
172. We consider the evidence of Mr Holbrook as to the probability of the pilots being able to see the lower part of the Mull to be of considerable importance - evidence which unfortunately was not before the Air Marshals when they carried out their reviews. For the reasons already given we do not think that the Boeing simulation merits the status which has been accorded to it in the past, and that even if there were some last minute manoeuvre of the aircraft it cannot be said that there was absolutely no doubt whatsoever that it was initiated by pilots who were in control of the aircraft.
173. It follows that the Air Marshals were not justified in concluding that the pilots were in control 4 seconds before impact, or at any time after the way point change. In short it has not been established to the required standard of proof that it was the voluntary action of the pilots which caused the aircraft to fly into the hill.
174. In carrying out our terms of reference, we have considered the justification for the Air Marshals' finding of negligence against the pilots of ZD 576 against the applicable standard of proof, which required "absolutely no doubt whatsoever". In the light of all the evidence before us, and having regard to that standard, we unanimously conclude that the reviewing officers were not justified in finding that negligence on the part of the pilots caused the aircraft to crash. (the bold is theirs not mine)
175. We consider it appropriate to identify those matters to which we have had regard which were not before the Air Marshals when they considered the investigating board's report:
(a) the more detailed evidence of Mr Holbrook as to the weather conditions at sea, and the probability that the crew would have seen the land mass from some distance offshore;
(b) the evidence of Mr Perks, Witness A and Squadron Leader Burke;
(c) the deficiencies in the Boeing simulation with particular reference to the facts that
(i) it did not take account of FADEC and
(ii) it used a postulated speed and ROC which have been shown to be incompatible; and
(d) the possible effect of contamination in the hydraulic fluid in the integrated lower control actuators, as referred to in the US Army report of June 1997.
176. How could it be that a very experienced crew, having planned to fly VFR, having taken when probably visual with the Mull the appropriate steps to alter course, when there was nothing to prevent them flying northwards within sight of the coast, flew into the Mull? It is as Sir John and Sir William speculatively described "incomprehensible" (Q 342) and "astonishing" (Q 377). We shall never know(my bold).
JB