The Mull of Kintyre Disaster: The Cause: Failure of machinery or pilot error likely: 'No reason whatsoever to suspect that we are dealing with anything but a tragic accident', police chief says

THE SPEED with which the authorities dismissed any suggestion that sabotage was responsible for the helicopter crash suggests that they have a good idea of what happened.

On the 8am BBC radio bulletin yesterday, Leslie Sharp, Chief Constable of Strathclyde Police, said: 'There is no reason whatsoever to suspect or suppose that we are dealing with anything other than a tragic accident.'

Indeed, the likelihood of an IRA attack is remote. They could not conceivably hang around the remote Mull of Kintyre with anti- aircraft guns waiting on the off- chance for a helicopter to fly over. And if they had blown up the helicopter, they would have loudly proclaimed their success. Moreover, the security at the RAF base at Belfast from where the helicopter took off, Aldergrove, is very tight and has never been broken.

This leaves two possibilities, a catastrophic equipment failure or what is technically known as 'controlled flight into terrain', hitting the ground because the pilot is not aware of the altitude.

Clearly, at this stage any explanations are speculative but there are pointers. The lack of a mayday call suggests that the pilots were taken by surprise. It also suggests that they were flying relatively low. The helicopters are designed to survive the failure of one engine, and they are also equipped with an auto-rotation mechanism which means that the blades continue turning even if the engines do fail, allowing the helicopter to land in a kind of glide. If anything had happened at a reasonable height, there would have been time to send out a mayday.

Second, the wreckage was apparently not strewn over a large area. This tends to imply that the aircraft broke up on impact.

The investigation will be carried out by an RAF board of inquiry with help from the Department of Transport's air accidents investigations branch. They will have started by examining the location of the wreckage and looking at the weather conditions and any information from air traffic control. The investigation will be made more difficult by the lack of a black box flight recorder.

The pilots were flying in unrestricted airspace once they had left the Belfast area which means they would not have had to file a flight plan and they would not have been under air traffic control. They would have been flying on a 'see and be seen' basis with the pilots being responsible for avoiding collisions with other aircraft.

The key question, therefore, is why the helicopter was so low. John Osmond, editor of Defence Helicopter magazine, said: 'If I had been flying that route, I would have taken the helicopter up to a nice safe level of 5,000ft or more and cruised at that level all the way, avoiding the Scottish peaks.'

One theory is that the Chinook, which had been returned from its major refurbishment about three months ago from Boeing, in Philadelphia, was subject to a height restriction because the new Mark 2 helicopter is virtually a new type of aircraft. One source said it has been unable to fly above a certain level as it had not yet been cleared to do so. The MoD refused to comment on this theory.

Another theory on why the helicopter was flying low was that the pilot wanted to give his VIP guests a good view. One former RAF pilot said: 'It's surprising how often VIP guests make that kind of request.' But he added: 'The RAF tend to be incredibly disciplined and it seems unlikely that the pilots would have broken the rules.' Aircraft accidents are usually a combination of events. In this case, the likely additional cause was that there was a so- called 'finger error'. The pilots would have keyed in their course to the newly-installed Global Positioning System which enables the pilots to know their location within a few metres. The GPS then matches their planned course and indicates to the pilots when to adjust direction.

A common occurrence is for pilots to make a slight error in keying the components which means that they are in the wrong place. The fact that a fireman reported that the craft appeared to have hit the ground, bounced, and hit it again suggests that the pilots may belatedly have realised their error and tried to pull up the craft.

The fact that the helicopter was not carrying weather radar was widely regarded by experts to be a red herring.

While Chinooks have been involved in a number of accidents, helicopter experts say their record is relatively good.

Helicopters, by their very nature, will always be more dangerous than fixed wing aircraft. It is for this reason that the Queen, with the exception of trips to Northern Ireland, is barred from flying in helicopters.

(Photograph omitted)