Chinook Evidence
John Purdey
I hope I still qualify as a courteous contributor by your standards. I have been trying to stay away from some of the recent contributions on the site - too many of which seem to have lost sight of what it is about. I welcome ShyTorque's contribution since as an operator he confirms what I said might have happened in my engineering report of Oct 2003 - note might - I do not know either.
I was, though, surprised to see your claim that there is "clear evidence that in the final couple of seconds or so of flight, the crew tried to pull up and turn left".
I have not seen this clear evidence anywhere, indeed perhaps I could remind you of Robert Burke's evidence to the HofL - evidence that is also supported by the AAIB investigator. Perhaps you would be kind enough to give us the source of your comment
Evidence of Squadron Leader Robert Burke
107. Squadron Leader Burke had extensive experience in flying helicopters including Chinooks Mks 1 and 2 and was described by his unit commander in April 1993 as having air-testing skills on the Puma and Chinook which were unique. He was able to provide us with useful information about the problems which he had experienced when testing Chinooks. At the outset of the investigation into the accident he was contacted by Mr Cable and had two or three telephone discussions with him in relation to control positions (QQ 658, 662). Thereafter he had nothing further to do with the Board of Inquiry.
108. After Squadron Leader Burke gave evidence, Group Captain Pulford submitted a statement to us (p 68 of HL Paper 25(ii)) in which he sought to explain why Squadron Leader Burke had not been asked to give evidence to the investigating board. He stated that as the Chinook maintenance test pilot "his flying was conducted in accordance with limited and pre-determined flight test schedules and he therefore lacked the operational currency to provide relevant evidence to the inquiry". This reasoning seems to assume that problems which Squadron Leader Burke might have encountered on test would not or could not occur in operational flying - an assumption whose justification we feel to be in doubt.
109. Squadron Leader Burke spoke to having experienced two engine run ups on the ground at the Boeing factory in Philadelphia while flying with an American Army test pilot (Q 655) and similar run ups when testing the overspeed limiter on the ground at Odiham (Q 680). He also spoke to problems with the multi-point connectors which went from the engines into the DECU. These were of bad design and liable to be displaced by vibration which then produced a power interruption. Although there was a back-up system this did not always work and on two or three occasions pilots had lost control of the engine condition lever. As a result squadrons introduced a procedure whereby crewmen every quarter of an hour checked that the connections had not been displaced in flight (QQ 677-9).
110. At the time of the accident DECUs still presented recurring problems. They were removed from the aircraft when something had gone wrong and returned to the makers who on many occasions could find no fault (QQ 698-9).
111. In relation to possible jams Squadron Leader Burke explained that, due to the complexity of the Chinook control system, a jam caused by a loose article such as the balance spring in the broom cupboard in one of the three axes, pitch, yaw or roll, could lead to quite random results in all three axes sometimes and certainly in two of them. He had personal experience while lifting off from the ground of a jam in one axis affecting the other two (Q 935). He also referred to the problems of DASH runaways in Chinooks of both marks causing temporary loss of control of aircraft (Q 929).
112. Finally, Squadron Leader Burke commented on the rudder input of 77 per cent left yaw found in the wreck of ZD 576:
"That is an enormous rudder input. It is unthinkable to put that in at high speed. As I may have explained, particularly in the Chinook but in any helicopter, the helicopter does not use the yaw input for control once you have gone over 20 knots. It puts an enormous strain on the aircraft because you obtain yawing control in the simplest way by tilting the rotors one left, one right. You are spinning the aircraft about its middle. It is quite difficult to do. The rudder is quite heavy on a Chinook. You have to make a real effort to put that amount of control in. The only conceivable reason that I can think of for putting that voluntarily in as a pilot is if you have partially lost control coming out and you are trying to counteract a yaw one way or the other" (Q 719).
113. Mr Cable told us that, though it was possible that this rudder input was applied before impact, it was also possible that it was due to the force of the impact itself (Q 999).
Can I also remind you that there were two entries on the Supplementary Flight Servicing Register that had potential relevance as a cause of, or a contributory factor to, the accident. These were: Serial 2, SI/CHK 57 relating to the security of the DECU connectors and which applied to the HC2 version only, and Serial 4, a special check on the security of the Collective Balance Spring Bracket Mount called for by S Eng O 7 Sqn following an incident [where the bracket became detached as found in the wreckage of ZD 576] on ZD576 on 10 May 1994. Although the Board included the Supplementary Flight Servicing Register in Annex AK Extracts from ZD576 F700 and MWO, they did not include the Supplementary Flight Servicing Certificate (which was eventually supplied by MOD in 2001) and they did not question whether these checks had been carried out and whether the people who did them were trained and competent/authorised to do so.
Are you still sure that a loss of engine or flight control functions could not have caused or contributed to this tragic accident? Nobody else who has made full and proper assessment of all of the available evidence is!