By Caroline Wyatt and Stuart Hughes
The defence secretary has ordered a safety review of the RAF's fleet of Nimrod reconnaissance spy planes following an inquiry into a September 2006 crash in Afghanistan in which 14 people died. But the fleet is still considered safe enough to continue flying.
Concerns have been raised about fuel leaks on board Nimrods
The Ministry of Defence's Board of Inquiry was unable to examine the wreckage of Nimrod XV230 or the area near Kandahar where the aircraft came down because it was a Taleban stronghold and there were not enough troops to hold the site.
Much of the aircraft was destroyed or removed from the area and as a result the exact cause of the accident may never be known with certainty.
The sequence of events which led up to the crash was pieced together from the aircraft's flight recorder, air traffic control recordings, photographs taken at the crash site, the small amount of wreckage found and eyewitness testimony.
The Board of Inquiry (BOI) concluded that fuel probably escaped following air-to-air refuelling.
It said it leaked either from the main fuel tank or a fuel coupling.
The fuel made contact with a hot air pipe near tank seven after entering a gap between the insulation and ignited in under a minute.
A fire started and within five minutes the fuel in tank seven began to boil. It was then ignited by the fire and the plane exploded.
The BOI does not apportion blame but it does identify several factors that could have contributed to the disaster.
These include the age of some of the Nimrod's components, the RAF's maintenance of the fleet's fuel and hot air systems, and the lack of fire detectors and extinguishers within the area where the fire started.
But despite the problems highlighted by the report, Chief of Air Staff Sir Glenn Torpy has insisted the Nimrod fleet is still safe enough to continue flying.
Based on the world's first jet airliner, the Comet, the Nimrod was built at the height of the Cold War to track Soviet submarines.
HOW THE NIMROD CRASHED
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 underfloor by sensitive wiring.
The Nimrod XV230, the oldest aircraft in the ageing Nimrod fleet, was built to the so-called MR2 standard.
It was the first Nimrod to enter operational service with the RAF and had been flying since 1969.
The Nimrod was due to have been retired some years ago and a £2.2bn contract was agreed in 1996 to upgrade 21 Nimrod MR2 aircraft to Maritime Reconnaissance Attack 4 (MRA4) standard.
The programme involved the complete replacement of the aircraft's systems and more than 80% of its airframe, creating a virtually new aircraft.
However, rising costs and long delays have meant that the Nimrod MR2 will remain in service until at least mid-2010.
"The replacement Nimrod was originally called Nimrod 2000 - that tells you something," said Sean Maffett, an aviation commentator.
"All 21 MRA4s had been due to be in service by last year. Now the RAF is going to get 12 starting in 2010.
"There has just been one problem after another. It has been deeply disappointing and it has caused these old MR2 aircraft to be soldiering on much longer than they should have been."
'Eye in sky'
The Nimrod's capabilities in the field, however, are considered so vital that British forces simply can't afford to lose them.
Even though Britain is now using one unmanned drone to supplement the five remaining Nimrods in Afghanistan, no other aircraft is seen as having the same ability to deliver real-time battlefield video and information to British troops on the ground.
Without their "eye in the sky", troops taking on the Taleban would be fighting blind.
So the decision has been taken to keep Nimrods in the air.
"I can see no possibility of them being grounded because of their urgent operational tasks," said John Blakeley, a retired senior RAF engineer.
"In an ideal world, the Nimrod would be grounded. But we don't live in an ideal world so the Nimrod will carry on flying."