The evidence as to the value of fitting a Cockpit Voice Recorder (CVR) and/or an Accident Data Recorder (ADR) in an aircraft was spoken to chiefly by Mr Cable. In his report he expressed the matter thus:-

  "The absence of either an ADR or CVR resulted in considerable hindrance and protraction of the technical investigation. Both facilities commonly provide major benefit to the investigation of both fixed and rotary wing aircraft accidents and hence to the identification of measures aimed at preventing subsequent similar accidents. The availability of information from either source almost invariably expedites the investigation to a considerable degree and enhances the level of confidence in the final conclusions reached as to the causal factors, at times crucially. While it is preferable to have both data and sound recordings available a CVR alone can provide a considerable quantity of information, not only on crew and ATC communications but also on other sounds reflecting features of aircraft operation such as cockpit control selections, explosions, structural failure and characteristics of rotating machinery. Although typical CVR recordings are of relatively short duration and low fidelity, spectral analysis can provide detailed information on such parameters as the rotational speed of engines and rotors and on malfunctions such as impending transmission gearwheel failure and these facilities have been utilised to major effect in a number of AAIB investigations. For example, in the case of Chinook BV234 G-BWFC that crashed in the North Sea on 6 November 1986 with 45 fatalities (AAIB Report 2/88) CVR recording analysis had, within 48 hours of impact, pinpointed the component whose failure caused the loss of the aircraft together with data on the progression of the failure. Such analysis can also provide a high level of confidence as to the satisfactory operation of engines, transmission and rotors in the absence of malfunction. The AAIB Recorder Section estimates that a CVR typically costs around US$10,000-15,000 per aircraft, including both the unit and its installation".

  In the course of cross-examination Mr Cable was asked by counsel for the Tapper family: "Q.—....given that you don't have data from an Accident Data Recorder or a Cockpit Voice Recorder, there must be less confidence in your final conclusions than there would have been if you had all that extra data... that might otherwise have been available? A.—Yes, I think conclusions like this, like safety, are not absolute terms. There are levels of safety and levels of confidence. I have no doubts in the overall conclusions that I have drawn from my examination of the wreckage and accident site....Q.—But if an Accident Data Recorder had been installed and if you had found it functioning you would have a much greater degree of confidence in your conclusions. A.—I would have reached the point that I have reached much quicker. I would have more confidence in the quantitative value of the parameters, the impact parameters, the possible tolerances of those would be much lower. In general terms, at the end of the day, I don't believe it would have added greatly to the confidence in the conclusions I had reached. I have qualified my conclusions where I consider the evidence requires it".

  Later Mr Cable was asked by the solicitor for the Cook family: "Q.—Now, I am right, am I not, in understanding that you are confident in the conclusions which you have reached in your report...? A.—Yes, I am, with the qualifications that I have included there. Q.—What I think would be fair to say is with the appropriate recording equipment which we have heard about you may have been able to go further in your conclusions. A.—Oh, yes certainly. Q.—To take a simple example: If a pilot had been recorded as saying something about what was happening at the aircraft at the time of the crash you would have perhaps been able to conclude with further investigation that was at least a possibility? A.—Depends what it was. I am splitting hairs, but it depends if it related to an operational matter or an engineering matter. I mean it would clearly add quite a lot on the operational side to have heard a defined flight path leading to the accident. Q.—Would it be fair to say certainly in a civilian context that pilots can often have a measure of protection from such recording equipment when crashes take place in that such recording equipment may point to causes for accidents which in the absence of that recording equipment might leave the pilots being inappropriately blamed? A.—Yes, we have commonly found this".

  This last observation found an echo in a passage in a report (Annexe V) which was prepared for the Board of Inquiry by a principal psychologist of what I take to be the Institute of Aviation Medicine. After considering a possible scenario of events the author of the report wrote: "But the only possible source of evidence that could have cast some light on the crew's intentions and thoughts, a recording of their communications, was not available. At one stage in the investigation, because the RNS252 system was found in the wreckage switched off, evidence was sought to explain why a crew might choose to do without this essential equipment. Fortuitously data stored in the system survived the crash and only its recovery showed this line of inquiry to be a red herring. This fact provides a benchmark against which speculative explanations should be judged. The lack of CVR on the Chinook has two major consequences: The competence and skill of the crew are unavoidably but invidiously called into question in a speculative manner. And, if they did fail, the lessons that could have been learned from their tragic error are denied to their colleagues". H was asked: "Q.—...would you agree the lack of a Cockpit Voice Recorder had the consequences described here? A.—Yes".

  It was submitted by counsel for the Ministry of Defence that it was not easy to see how the issue of fitting either a CVR or an ADR could be dealt with within the parameters of section 6 of the 1976 Act and that in any event it would not be possible for the court to say that it would have been a reasonable precaution to have fitted either of these without more evidence, for example about their cost and whether other items of equipment might require to be omitted to make way for them. Counsel for the remaining families on the other hand invited me under reference to section 6(1)(e) of the Act to support the recommendation made by the Board of Inquiry to the effect that such recorders should be fitted in all RAF Chinook aircraft at the earliest opportunity and by Mr Cable that fitment of such recorders should be considered. He drew attention to the benefits of such recorders as disclosed by the evidence and submitted that anything which assisted in providing an explanation for what had happened would in generality almost always be of some benefit to the relatives of victims of tragedies such as this who quite naturally craved an understanding and explanation for what had occurred. Similarly, it might provide some consolation in supporting the hope that lessons would be learned which might prevent a repetition. Counsel also commented that no explanation had been tendered to the inquiry by the Ministry of Defence for the failure to implement previous recommendations to the same effect made by RAF Boards of Inquiry into two earlier accidents involving Chinook helicopters.

  A not dissimilar approach to that of counsel for the remaining families was taken by the advocate depute, counsel for the Tapper family and the solicitor for the Cook family. For my part, I think that the absence of either or both of a CVR and ADR is clearly relevant to the circumstances of the deaths in this case inasmuch as that absence has prevented those circumstances being investigated as fully as they might otherwise have been. On the other hand, notwithstanding certain comments which I have read in the press, I have no power to make recommendations in this respect which would be binding on anyone, least of all the Royal Air Force. But I would certainly endorse the view that it would be highly desirable to fit Cockpit Voice Recorders and Accident Data Recorders in all RAF Chinook helicopters as soon as possible unless there are overriding military or operational reasons to the contrary (and there was no evidence to that effect before the inquiry).