Select Committee on Public Accounts Forty-Fifth Report



18. The RAF convenes a Board of Inquiry to investigate the cause of all significant air incidents and accidents. In line with this procedure, a Board of Inquiry was established to examine the crash of Chinook ZD-576 on the Mull of Kintyre on 2 June 1994. The Board of Inquiry found the pilots of ZD-576, Flight Lieutenants Jonathan Tapper and Rick Cook, guilty of gross negligence in causing the crash of their aircraft. According to the then extant RAF regulations, a finding of gross negligence must be substantiated by a burden of proof that there is "no doubt whatsoever." In the case of ZD-576 the Committee considers that the burden of proof was not, and cannot be, sustained by the evidence available. Areas of doubt relate to the condition of the Chinook Mark 2 fleet at entry to Service, to the incomplete nature of the technical evidence from the crash of ZD-576, and to negligence being found in the absence of any other explanation rather than being positively identified as the cause.

At entry to Service and the time of the crash of ZD-576 the Chinook Mark 2 fleet was experiencing widespread and repeated faults caused by the FADEC software

19. On entry to service there were a number of faults across the Chinook Mark 2 fleet,[46] including on ZD-576, stemming from the FADEC system software. The Committee asked the Department to provide a full analysis of the faults reported on the FADEC between the time the helicopter entered service and October 1994. The Department declined to answer the question on the basis that to do so would take some six months at considerable cost.[47] The faults with the FADEC led to doubts as to the reliability and safety of the aircraft at the time and make it very difficult to rule out categorically a technical fault as at least a contributory cause of ZD-576's crash:

      (i)  Since its introduction into Service the Chinook Mark 2 has experienced six engine run-ups and one run-down whereby the engine speed would change without the pilot requiring it.[48] The Department state that all these incidents occurred on the ground; but an in-flight run-up or run-down of the engines would have had serious consequences. These problems stemmed from faults in the FADEC software[49] and were part of the reason that the operation of the aircraft was restricted to lower than maximum payloads;

      (ii)  During the aircraft's initial operating period the engine fail caption warning light in the cockpit would come on, requiring the crew to go through the engine failure emergency drill which takes around a minute. Although spurious, those false alarms were warnings of a potentially catastrophic failure which had to be taken seriously by the crew. Again those faults originated in the FADEC software;[50]

      (iii)  Although the Department have referred to the faults during the initial in-service operation of the Mark 2 as "nuisance" faults[51] nonetheless the FADEC software was upgraded to eliminate them. The upgrade was not completed until the aircraft had been in-Service for well over a year and after the crash of ZD-576;[52]

      (iv)  The cause and significance of the faults experienced during initial aircraft deployment are now well understood. However, at the time of the ZD-576 crash they were not,[53] and both the aircrew and groundcrew operating the aircraft could not have been sure of their implications for the safety of the aircraft and would have had to react to every fault accordingly;

      (v)  The faults were such that test flying at Boscombe Down was suspended in June 1994. Test flying did not re-start for five months until the manufacturer of the FADEC system had provided adequate explanations of why the faults were occurring and what the implications were for the safe operation of the aircraft.[54] Throughout this period operational squadrons continued to fly the aircraft.

The technical evidence relating to the performance of the FADEC systems on ZD-576 was incomplete

20. As part of the post-crash investigation, the Air Accident Investigation Branch (AAIB) conducted a technical examination of the wreckage to support the RAF Board of Inquiry. Part of that examination related to the engine systems and "in view of the reports of a number of ongoing service difficulties experienced with the operation of the FADEC, the engine change units and the FADEC were examined in some detail."[55] However, the technical evidence relating to FADEC performance was incomplete because:

      (i)  The prime source of data on the performance of the FADEC system was the Digital Engine Control Unit (DECU) from each of the two engines. Data was recovered from only one of the DECUs because the other had been irretrievably damaged by post-impact fire. [56] It is not, therefore, possible to be absolutely definitive (as required for a finding of gross negligence) that the FADEC was performing normally at the time of the crash;

      (ii)  The FADEC system had caused repeated spurious failure warning lights to be displayed in the cockpit, a source of distraction for the crew. The Department stated that if FADEC had been a factor in the crash of ZD-576 the status of the warning lights would be key substantiating evidence. In evidence, the Department advised that "there were no lights on in the dashboard at the time."[57] The Department have subsequently informed the Committee that, although they are confident that the warning lights for number 2 engine were not illuminated before impact, that they do not know if the lights for number 1 engine were on or off.[58] Again, it is not possible to reach a definitive conclusion either that the lights were off and thus did not provide a distraction to the crew as they approached the Mull of Kintyre, or that the FADEC was working normally.

Negligence should only be found when it is definitively the cause of a crash, not simply as a last resort in the absence of any other more convincing explanation

21. RAF Regulations extant at the time of the crash investigation required that the burden of proof for negligence demonstrate "no doubt whatsoever." In turn this requires that there should be proof positive that the actions of the aircrew caused the crash:

      (i)  In the case of ZD-576, in the absence of a conclusive cause, the Reviewing Officers to the RAF Board of Inquiry selected negligence as the most likely cause because "none of the possible scenarios was so strong as to have been likely to have prevented such an experienced crew from maintaining safe flight."[59] We find that logic flawed. The proper approach should have been to reach a finding of gross negligence only if it could be positively ruled in. We consider that, had that proper approach been taken a finding of gross negligence would not have been returned;

      (ii)  Because ZD-576 crashed in Scotland, a Fatal Accident Inquiry was held, conducted by the Sheriff Sir Stephen Young. Having considered evidence from all parties the Sheriff could not find a definitive cause for the accident. The Fatal Accident Inquiry works to a lesser burden of proof in determining cause, its findings being based on a balance of probabilities rather than no doubt whatsoever. However, even against this lesser burden of proof the Sheriff could not agree with the Board of Inquiry's finding of gross negligence. We are surprised that the Department have not taken on board this learned legal judgement. Indeed, we believe that the Department should now recognise and should be guided by the decision of the properly constituted Scottish court, and should recognise that court's superior standing over their own domestic procedures. We regard the Department's preference for the results of their own procedures as constituting unwarrantable arrogance;

      (iii)  In crash investigations, particularly in civilian aviation, the most compelling evidence in determining a cause comes from cockpit voice and accident data recorders—black boxes. Chinook ZD-576 was not fitted with either a cockpit voice recorder or accident data recorder despite comments from three previous Chinook RAF Boards of Inquiry.[60] As a result there is inevitably a degree of speculation as to the cause of the loss of ZD-576. We do not understand how, given the absence of the definitive information that black boxes could have provided, the Board of Inquiry and the Department can have no doubt whatsoever that crew negligence caused ZD-576 to crash.


22. RAF Boards of Inquiry are convened to establish the causes of incidents and accidents involving RAF aircraft and make recommendations for future safety improvements. Until recently they also apportioned blame for accidents. The decision in 1997 to drop the requirement for Boards of Inquiry to apportion blame was a welcome change. Figure 1 illustrates how the Board of Inquiry process works with specific reference to the case of Chinook ZD-576. It demonstrates that there are still elements of the Board of Inquiry process that could lead to controversy.

23. We strongly recommend that the Board of Inquiry process should be revised to ensure that those officers have management and command responsibility for the aircraft and the personnel involved do not influence or control the findings of Boards of Inquiry.

Evidence, Appendix 1, Section 3, response to Qs 102-103, 112-113, para 5, pp 33-35 Back

47  Evidence, Appendix 2, covering letter para 2, p42 Back

48  Evidence, Appendix 1, Section 3, Qs 102-103, 112-113, para 4, pp 33-35 Back

49  Evidence, Q106 and Evidence, pp 1-2, paras 4 and 6 Back

50  ibid Back

51  Evidence, Appendix 1, Section 1, para 6, p32 Back

52  Evidence, Q248 Back

53  Evidence, Appendix 1, Section 2 (not reported) Back

54  Evidence, Appendix 1, Section 2 (not reported) Back

55  Air Accident Investigation Branch, Statement to the Board of Inquiry, para 7.3, and Evidence, Appendix 1, Section 1, para 8 (not reported) Back

56  ibid, para 7.3.4 and RAF Board of Inquiry Proceedings, para 35b (not reported) Back

57  Evidence, Q33 Back

58  Evidence, Appendix 1, Section 3, response to Q33, para 2, pp 37-38 Back

59  ibid, Section 2 (not reported) Back

60  Evidence, Appendix 1, response to Qs 240-241, para 1, pp 38-39 and Evidence, Appendix 2, response to Q18, pp 51-53 Back

previous page contents next page

House of Commons home page Parliament home page House of Lords home page search page enquiries index

© Parliamentary copyright 2000
Prepared 30 November 2000