F-35 fighter jets grounded while investigation into engine fire is carried out

The aircraft was to make its debut at Farnborough Airshow, but is now being examined by the US military

The world's most advanced fighter jet has been grounded by US military investigators following an engine fire, it was revealed yesterday.

Hopes of seeing the world's most advanced fighter jet make its debut in Britain faded last week faded after the US military refused to allow it to fly while its investigation continued. The US F-35 joint strike fighter, in which Britain has a stake, had been expected to be the star attraction at this weekend's Royal International Air Tattoo at RAF Fairford, which ends today. It was also expected to star at this week's Farnborough Air Show, opening tomorrow.

But an aborted take-off in which part of the engine ripped out through the top of the plane and caused a fire, as an F-35 was preparing to take to the skies from an air base in Florida last month, resulted in the entire fleet being grounded.

"At this time, I do not have sufficient information to return the F-35B and F-35C fleet to flight," Vice Admiral David Dunaway, who heads the US Navy's air systems command, said in a memorandum obtained by Reuters news agency. He claimed there was "no discernible event that represents a root cause".

As for the chances of the fighter coming to Britain this week, he said: "There are specific additional evaluation conditions required to support the Farnborough Air Show in the UK, including the ferry flight across the Atlantic and performance in the air show itself."

Investigations by the US military are continuing, and an update is expected by Wednesday.

British defence officials admitted yesterday that the F-35's appearance at Farnborough Air Show is in doubt. In a statement, a Ministry of Defence (MoD) spokesperson said: "The safety of pilots and aircraft has to be our priority. We fully support the decision not to grant clearance for the aircraft to make their first transatlantic flight to the UK until the technical investigations are complete. Should clearance be granted in the coming days, we will work with the US marine corps to facilitate the aircraft's participation in the Farnborough International Air Show."

The F-35 fleet grounding is "not expected to have a significant impact on the programme and we are on track for the UK's aircraft to achieve their initial operating capability in 2018", the spokesperson said.

But this is the latest in a series of setbacks for the F-35, whose Lightning II variant is the state-of-the-art replacement for Britain's retired Harrier jump-jet fleet. Years of delays and technical problems have caused the cost of each plane to soar to £100m. Earlier this year, Michael Gilmore, the US military's chief weapons tester, called the software performance of the advanced stealth fighter "unacceptable".

Production was also disrupted after it was discovered last year that the fuel tank could explode if struck by lightning, along with a design fault which hindered the fighter from being able to descend rapidly to low altitude. Tests by the United States air force and Lockheed Martin, the aircraft's manufacturer, also discovered cracks in parts of the plane.

The number of fighters Britain is likely to end up buying has already been slashed from the 138 envisaged by the last government to about 48, and an order will not be placed until after next year's strategic defence and security review. In the meantime, Britain's new aircraft carriers will have to wait until the end of the decade before the planes they need are ready.

Responding to the news yesterday General Lord Dannatt, former chief of defence staff, said: "Where matters of safety are involved, rushing procedures just to be able to appear at Farnborough would be very unwise. Like all leading-edge technology, a programme like the F-35 is bound to be prone to delays and cost overruns. I hope the MoD has made sensible provision for this."