Select Committee on Chinook ZD 576 Report


31 January 2002

By the Select Committee appointed to consider the justification for the finding of those reviewing the conclusions of the RAF Board of Inquiry that both pilots of the Chinook helicopter ZD 576 which crashed on the Mull of Kintyre on 2 June 1994 were negligent.



1.  On 2 June 1994, an RAF Chinook Mark 2 helicopter, ZD 576, crashed on the Mull of Kintyre. All those on board the aircraft were killed in the crash and the aircraft sustained catastrophic damage.

2.  RAF rules in force at the time provided that deceased aircrew could be found negligent only where there was absolutely no doubt whatsoever. The RAF investigating board concluded that the most probable cause of the accident was that the crew had selected an inappropriate rate of climb to overfly the Mull. However the investigating board made no finding of negligence on the part of the pilots; nor did the two station commanders who reviewed their findings. Nevertheless the two Air Marshals to whom the investigating board's report was submitted in turn concluded that the pilots were negligent in that they failed to take appropriate action when approaching deteriorating weather near the Mull. If they intended and were able to maintain visual flight they should have slowed down, turned away or turned back. If on the other hand they were forced by the presence of cloud to change from visual to instrument flight, they should have climbed to safety altitude at maximum power while turning away. It appeared to both the investigating board and the Air Marshals that the aircraft had flown straight towards the Mull without altering course for some 20 or more seconds before the crash.

3.  The House of Lords appointed us, in July 2001, to consider whether this finding of negligence was justified. In preparing this report we have not only considered the evidence which was before the investigating board and hence the reviewing Air Marshals, but also additional evidence both oral and written. This additional evidence related among other things to the weather in the area at the time of the crash, to various mechanical problems which had affected Chinook Mk 2 helicopters since their introduction into RAF service, and to what reliance could be placed upon the results of a mathematical simulation carried out by the aircraft manufacturers, Boeing, to determine the movements of the aircraft during its last few seconds of flight.

4.  Information extracted from the navigation equipment showed that, when the aircraft was 0.95 nm from the point of impact on a given bearing, a "way point change" was made to the navigation equipment to show the course and distance to Corran in Argyll, the next staging point on the intended route. There was no information as to the time this change was made, or the course and speed of the aircraft. The same equipment also produced an approximate height for the aircraft at an approximate number of seconds before impact, but neither position nor speed. A cockpit instrument showed a certain speed at impact. These results were much relied upon by the investigating board and the Air Marshals as demonstrating the final movements and speed of the aircraft.

5.  From this information, and from certain other information as to the position of the aircraft and some of its components at impact, Boeing concluded that the aircraft had made a final "flare"[1] upwards some 4 seconds before impact, and that for an unspecified time before this the aircraft was climbing at a rate of 1000 ft per minute at an airspeed of 150 knots, which with a tail wind of 25 knots gave a groundspeed of 175 knots or thereabouts.

6.  For reasons set out in our report, we consider that Boeing's conclusions cannot be relied upon as accurate. Since these conclusions are the basis for the conclusions of the investigating board and the Air Marshals that the aircraft was under control at the time of the final flare, it follows that there is insufficient evidence to the required standard of proof that this was the case.

7.  The additional evidence which we heard as to the weather came from a yachtsman who was sailing near the Mull at the time. He considered that when he saw the aircraft some 300 yards away the crew would have been able to see the land mass of the Mull. There was evidence before us from experienced helicopter pilots that, when a way point change is made to the navigation equipment, it is usual for pilots to change course towards the next way point at that time or shortly afterwards. In these circumstances we concluded that there could not be said to be absolutely no doubt whatsoever that the pilots intended to overfly the cloud-covered Mull; indeed the opposite is a distinct possibility if not more likely.

8.  We heard a good deal of evidence about mechanical problems suffered by Chinook Mk 2s. Some of these problems were intermittent, leaving no trace, and others were readily detectable. Although no trace of any mechanical fault, other than a defective radar altimeter, was found by the Air Accidents Investigation Branch inspector, he was unable to dismiss the possibility of an undemanded flight control movement, an engine run up or a control jam having occurred. Any of these events could have had a serious effect upon the crew's ability to control the aircraft. Once again we consider that it could not be said that there was absolutely no doubt whatsoever that some mechanical failure had not caused a loss of control of the aircraft.

9.  It is not our role to determine the likely cause of this accident, and indeed on the evidence which we have heard and read it would be impossible to do so. We are nevertheless satisfied, on the evidence before us and against the standard of "absolutely no doubt whatsoever", that the Air Marshals were not justified in finding that negligence on the part of the pilots of ZD 576 caused the crash.

1   A rapid change in pitch angle of the aircraft, either to slow down or to climb quickly. Back

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