A file picture of a pre-production model of the new stealth F-35 fighter. (AP)

Feb. 23: The Pentagon said yesterday that it had grounded all its new stealth F-35 fighter jets after an inspection found a crack in a turbine blade in the engine of one of the planes.

The suspension of flights comes at an awkward time for the military, which is facing automatic budget cuts that could slow its purchases of the planes. The Pentagon grounded all three versions of the jets — for the Air Force, the Navy and the Marines — on Thursday while it investigated the problem.

Lockheed Martin, which makes the high-tech plane, said 64 of the jets would be affected. The Pentagon estimates that it could spend as much as $396 billion to buy 2,456 of the jets by the late 2030s. But the programme, the most expensive in military history, has been plagued by cost overruns and delays, and it could easily become a target for budget cutters.

The Marines also had to suspend operation of their version from January 18 to February 13 because of a problem with a crimped hose in the fuel system.

The Pentagon office that runs the programme said the crack in the turbine blade was discovered on Tuesday in a routine inspection. The crack occurred on a test plane at Edwards Air Force Base in California. The blade is being shipped to a plant in Connecticut, where the engine manufacturer, Pratt & Whitney, will inspect it and look for the problem’s cause.

Matthew C. Bates, a spokesman for Pratt & Whitney, said none of the other F-35s had suffered any cracks. The F-35 programme office in the Pentagon said in a statement that it had suspended the flights as a precaution until the investigation was completed and the cause of the cracking was fully understood.

The turbine problem, first reported by Politico Pro, arose as the Pentagon has sought to persuade Congress to cancel the automatic cuts, which could force the military to reduce its budgets by about $500 billion over the next 10 years.

The first instalment of the cuts is scheduled to start on Friday, and it may force the Pentagon to delay buying three of the approximately 30 F-35 planes it had planned to order this year.

“We don’t know the severity of the problem with the turbine blade,” said Richard L. Aboulafia, an aviation analyst at the Teal Group in Fairfax, Virginia. “It could be a one-off or it could be something that needs more attention. But either way, given the political scrutiny and the concerns about the plane’s cost and performance, this is a very bad time to have a problem.”

The F-35 was conceived as the Pentagon’s silver bullet in the sky — a state-of-the art aircraft with advances that would easily overcome the defences of most foes.

The radar-evading jets would dodge sophisticated anti-aircraft missiles and give pilots a better picture of enemy threats while enabling allies, who want the planes, too, to fight more closely with American forces.

But the ambitious aircraft instead illustrates how the Pentagon can let huge and complex programmes veer out of control. The programme has run into other technical problems and nearly doubled in cost as Lockheed and the military’s own bureaucracy failed to deliver on the most basic promise of a three-in-one jet that would save taxpayers money and be delivered speedily.

Behind the scenes, the Pentagon and Lockheed Martin had also engaged in a conflict of their own over the costs, though both sides now say that the relationship has improved and that the programme is making progress. The number of test flights had picked up, and the Marines said before the grounding this week that they were about to shift from simply testing the planes to starting to fly them operationally.

The Pentagon had also reached new contracts recently with Lockheed and Pratt & Whitney that lowered the cost of each aircraft body and engine. Bates, the Pratt & Whitney spokesman, said a similar turbine blade in an engine built for testing purposes also cracked in 2007. But he said the blade was redesigned after that, and this week’s failure did not appear to be related.