In a serious setback for the most advanced fifth generation of United States, the F 35 was suspended from flying as Pentagon detects a serious crack in one of the fighter’s engine.

The Pentagon on Friday suspended the flights of all F-35 fighter planes after a routine inspection revealed a crack on a turbine blade in the jet engine of an F-35 test aircraft in California.

It was the second grounding of the warplane in two months. The fault was detected during a routine inspection of an air force version of the jet (F-35A) at Edwards Air Force Base in California, said the Pentagon.

Different versions are flown by the navy and the marine corps. All have been grounded.

The F-35 is the Pentagon’s most expensive weapons programme. with a cost of nearly $400bn (£260bn).

The Pentagon said flight operations would remain suspended until the root cause is established.

Friday’s order was the second time in two months planes from the F-35 range have been grounded.

The F-35 program office said it was too early to know if this was a fleet-wide issue, but it was suspending all flights until an investigation was completed.

It said it was working closely with Pratt & Whitney, the United Technologies Corp unit that builds the engine, and Lockheed Martin Corp, the prime contractor for the radar-evading warplane, to ensure the integrity of the engine and return the F-35 fleet to flight as soon as possible.

The Pentagon’s F-35 program office began notifying the chiefs of the U.S. Air Force, Navy and Marine Corps late on Thursday about the engine issue and decision to ground the planes, said Kyra Hawn, a spokeswoman for the Pentagon’s F-35 program office.

She said that during a routine inspection at Edwards Air Force Base in California on February 19 inspectors found a crack on a low pressure turbine blade that is part of the F-35′s F135 engine. The blade was on F-35 A-model, or Air Force variant, which takes off and lands from conventional runways.

Engineering teams would remove the blade and ship it to Pratt’s engine facility in Middletown, Connecticut, for more thorough evaluation and root cause analysis. An initial analysis was expected next week, she said.

The grounding comes on the heels of a nearly month-long grounding of the Marine Corps variant of the new warplane after a manufacturing defect caused a fuel line to detach just before a training flight in Florida.

The Marine Corps variant of the F-35, which takes off from shorter runways and lands like a helicopter, was grounded for nearly a month after a fuel line detached just before a training flight at Eglin Air Force Base in January.

That issue was later found to be caused by a manufacturing defect. The Pentagon and the U.S. Navy lifted flight restrictions on the B-model of the plane on February 13.