Read the background and see the documents on Mick Smith's defence blog

The board of inquiry into the explosion that killed 14 crew of an RAF Nimrod has been reconvened, families of the dead servicemen were told last week.

The decision comes after a series of documents were passed to The Sunday Times describing how hundreds of gallons of fuel leaked from the aircraft during mid-air refuelling on a number of occasions.

The board of inquiry is believed to have blamed leaking fuel for the explosion over Afghanistan in September last year but was unable to specify the likely cause of ignition.

One of the documents, the report of an internal inquiry, warned that the aircraft were so old that they would suffer more“unexpected failures”. It described how a cooling duct in the bomb bay of another aircraft ruptured in November 2004.

A jet of superheated air was directed straight onto the fuel tank at the base of the starboard wing. But the incident occurred as the aircraft was returning to base at RAF Kinloss so the blast of air was not focused on the fuel tank for long.

Tests showed it would have been superheated to temperatures of 310?C to 424?C, well above the 260?C spontaneous ignition point of Avtur, the fuel used by the Nimrod.

The pilot of the aircraft that exploded over Afghanistan initially reported a fire in the bomb bay. In an attempt to reach Kandahar air base, he brought the aircraft down from 23,000 ft to 3,000 ft in 90 seconds.

A Harrier aircraft followed the aircraft down and saw the starboard wing explode first, followed a few seconds later by the rest of the aircraft. The base commander said in the inquiry report that more such incidents were likely to occur because the Nimrod was 10 years past its “out of service” date. “The unexpected failure should be ever at the forefront of our minds,” he said.

The families of the dead men were also told last week that all the recommendations made by the internal inquiry into the ruptured duct had now been implemented.

Yet in a parliamentary written answer Adam Ingram, armed forces minister until Gordon Brown’s reshuffle, said one recommendation for the introduction of a hot air leak warning system was rejected because the ruptured duct was “an isolated incident”. He was responding to a question put by Ian Liddell-Grainger, Conservative MP for Bridgwater in Somerset who is pursuing the interests of one of the families.

Ingram also said that while that specific duct had been replaced, a recommendation that all such ducts across the aircraft should be replaced had been delayed and replacement would not begin until December.

A draft board of inquiry report into the Afghanistan explosion has been circulating among senior officials at the Ministry of Defence and RAF officers since early May. The families were told they would see the report in June. This was later put back to September.

Officials said the board of inquiry had been ordered to look at one of the issues in the report again but would not say which and by whom.

An RAF spokesman said: “We need time to analyse all available evidence and this inevitably will mean that further work may be undertaken to ensure that all information and advice is considered.”

Despite a history of fuel leaks on the Nimrod fleet it has kept flying. Senior officers have also insisted it should continue the mid-air refuelling that caused the leaks.

The Nimrods, which are 35 years old on average, were due to have been upgraded by 2000 into a new aircraft, the MRA4, built using the old fuselages to save money.

The programme has been delayed to 2010 by a mix of procurement bungles and funding cuts.

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