The RAF's Nimrod surveillance planes are to be withdrawn from operations overseas until the early summer to undergo safety modifications, defence minister Bob Ainsworth announced today.
An inquiry into the 2006 Nimrod crash in Afghanistan, which killed 14 people, recommended the replacement of fuel seals and engine bay hot-air ducts to improve the safety of the fleet.
The modification work was due to be completed by 31 March, but has been delayed, said Mr Ainsworth.
Technical experts advised that Nimrods should not fly after the end of March unless they have had their hot-air ducts replaced.
The temporary halt to overseas operations has been ordered to speed the modification programme.
Meanwhile, routine UK-based flights will be reduced because of the reallocation of engineers from the Nimrods' home bases at RAF Kinloss in Moray and RAF Waddington in Lincolnshire to the modification programme.
In a written statement to the House of Commons, Mr Ainsworth said the delay was caused by problems with the provision of replacement fuel seals.
The temporary suspension of overseas operations "will allow us to free up the maximum number of aircraft for the modification programme while also allowing Nimrod to continue with its critical homeland security tasks", he said.During this period, we will use other UK and coalition assets to maintain an effective surveillance capability overseas."
He added that the reallocation of engineering personnel "will cause a temporary reduction in routine UK-based Nimrod flying but will not affect our ability to protect UK interests at home".
Mr Ainsworth said: "We have reassessed the situation in the light of these developments and concluded that the Nimrod fleet remains airworthy and safe to fly, subject to the measures outlined above."
A new report by defence technology company QinetiQ does not identify any significant airworthiness issues and does not alter previous assessments that the Nimrod remains safe to fly, said Mr Ainsworth.
The Nimrod initially entered service in 1969 and was upgraded in the 1970s. The Nimrod MR2 is due to continue in service until it is replaced by the MRA4 version of the craft, which is expected to enter service around 2011.
The Afghanistan crash, which caused the biggest loss of life among British forces in a single incident since the Falklands War, was only the fourth involving a Nimrod in 36 years of operations.
A Ministry of Defence inquiry found that the accident was probably caused by a mid-air fuel leak.
The Liberal Democrat defence spokesman Nick Harvey said: "This is in effect an admission by the Government that the Nimrod fleet is not safe to fly, and has not been for years.
"It is disgraceful that it has taken so long for ministers to take action to ground unsafe aircraft which have already claimed the lives of our service personnel and are still putting others at risk.
"RAF personnel and the coroner in the Nimrod inquest have been saying for months, if not years, that these planes are not airworthy. Why has it taken so long for the Government to listen?
"It also must be asked why it is deemed safe for these aircraft to continue to fly for a moment longer, let alone another three weeks, without the necessary replacement of their hot air ducts.
"It is shameful that MoD complacency and penny-pinching has put the lives of our servicemen and women at risk for so long."
Sergeant Ben Knight, 25, was one of the 14 servicemen killed in the 2006 Nimrod crash.
His father, Graham Knight, described today's Government announcement as a "vindication" of what Coroner Andrew Walker and the families of victims demanded at the end of the inquest last May.
Mr Knight, from Bridgwater, Somerset, said: "This is what we were asking for back after the inquest.
"We all said that we would like these repairs and modifications to be carried out before they flew again.
"They said 'No, they're safe to fly'. It now appears they have been withdrawn.
"Have they been flying them since June without these safety modifications being done?
"Well, obviously the answer is 'yes'. Safety has been compromised since the inquest."
He added: "I think it is a vindication of what we said after the inquest and what Andrew Walker said."Reuse content