Page last updated at 16:23 GMT, Friday, 23 May 2008 17:23 UK

Nimrod design faults highlighted

By Sean Maffett
BBC News

RAF Nimrod
The government has defended the RAF Nimrod fleet's safety record

A coroner has made some damning judgements about the airworthiness of the whole Nimrod fleet, which has been an essential part of the Royal Air Force's frontline since 1969.

From a mass of impenetrable documentation, he teased out the extraordinary story that started with the Nimrod being developed in the 1950s from the world's first jet airliner, the de Havilland Comet.

To make the Nimrod into a military aircraft, the then Hawker Siddeley company added extra fuel tanks and a whole new bottom half to the Comet's fuselage.

Crucially, they also changed the engines, and that meant installing a hot air pipe system to start the new Spey engines.

This hot pipe system crosses the centre section of the aircraft and enters the wings, where the engines are, through an area that was to become well known to the inquest - called Dry Bay 7.

I am satisfied that the design modifications to the MR2 made the aircraft unsafe to fly
Coroner Andrew Walker

This is the area around the new number seven tanks, and it also contains fuel feed pipes.

That should not have been a problem, since the hot air system was only used for engine starting.

But when the early Nimrod MR 1 was developed into the MR2 version in the late 1970s, they added an extra cooling pack for all the new electronic equipment.

This packs work off hot air, from the cross feed pipe, and that meant the pipe had to be in use continuously.

In Dry Bay 7 the pipe, operating at temperatures of 400 to 500 degrees Celsius, was next to the large fuel feed pipes.

'Serious flaw'

That was a serious fire hazard, and it should have alerted the continuous safety assessment systems operated by the RAF and the aircraft maker, now BAE Systems, to the potential hazards.

But as the coroner Andrew Walker said: "I am satisfied that the design modifications to the MR2 made the aircraft unsafe to fly.

"This serious flaw in the design was not discovered despite a baseline safety case study undertaken by the (Nimrod) Integrated Project Team and the manufacturer."

1. Nimrod refuels in mid-air
2. Possible fuel over-flow from number one tank
3. Second possible source of leak is pipe couplings behind number seven tank
4. Leaked fuel contacts hot pipe and ignites
5. Fire and smoke alarms triggered in bomb bay and under floor by sensitive wiring

Mr Walker added that there had been a previous incident to a Tornado aircraft where fuel had been drawn into the lagging round a hot pipe, and had ignited, causing the loss of the aircraft.

There had been no follow-up on the Nimrod, despite a recommendation from an RAF board of inquiry.

He said: "This cavalier approach must come to an end.

"In my view it was this very source of ignition that, on the balance of probability caused the loss of Nimrod XV230 with all souls on board."

He went on to detail failures of the so-called Cassandra Hazard Log.

Had failures been properly recorded in this log and dealt with, the design flaw in the Nimrod fleet would have been discovered.

He said "I simply do not understand" how it can be that the Cassandra system assumed that there was a fire detection and suppression system in Dry Bay 7 when there was clearly no such system, and never had been.

What that meant for the crew of XV 230 was that they could do nothing to prevent the fire that developed into an explosive ignition of fuel in Tank 7 in the wing root.

The aircraft broke up as the crew were trying desperately to make it back to Kandahar airport.

The coroner added in his final verdict that "the deaths were in part the result of failures... on the part of the aircraft manufacturer and those responsible for the safety of the aircraft".

Huge problem

Responding to a question from Michael Rawlinson, for 13 of the 14 families, Mr Walker said that he would be recommending to the defence secretary that the whole Nimrod fleet should not fly again until the risks thrown up by the inquest have been reduced to a level known as ALARP - as low as reasonably practicable.

The Nimrod Integrated Project Team Leader had already said in evidence that this was not expected to happen until the end of 2008.

This presents the MoD with a huge problem.

The job the Nimrods are doing in both Iraq and Afghanistan is absolutely vital to the forces on the ground - not just British forces, but the forces of all the other various coalition partners, including the Americans.

There is no immediately available replacement aircraft for this work.

Duty of care

That will be why the Armed Forces Minister Bob Ainsworth immediately announced that the Nimrod will fly on.

This has, of course, set this coroner on yet another collision course with the government.

And although the coroner has no direct control over what the MoD does, the next stage in this saga is already developing as the Nimrod Review, set up by Secretary of Defence Des Browne last year, and headed by Charles Haddon-Cave QC, takes up the story where the coroner leaves off.

The coroner has made mention of the duty of care that the RAF and the MoD has towards its personnel, and he clearly feels that this duty has not been discharged.

The Nimrod Review may well include this consideration, but it will surely also be examining whether the failures demonstrated so clearly in Oxford these past three weeks have further ramifications for the safety management of all of the Royal Air Force's aircraft.

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