F-35 fighter jet fleet grounded by Pentagon

Different versions of the most advanced US fighter jet are flown by the navy and the marine corps

The US has grounded its entire fleet of 51 F-35 fighter jets after the discovery of a cracked engine blade.

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 Marine Corps variant (F-35B), a short take-off and vertical landing variant (STOVL), was grounded for nearly a month after a manufacturing defect caused a fuel line to detach just before a training flight in January.

The Air Force version takes off from, and lands on, conventional runways while the STOVL version takes off from shorter runways and lands like a helicopter.

The UK is buying the STOVL variant for its future aircraft carriers.

It is replacing the scrapped Harrier jet which had a range of 300 nautical miles, compared with the F-35's 450 nautical miles.

With a top speed of 1,200mph (1,930km/h), the F-35 can fly almost twice as fast as the Harrier, while it also has radar transparency and stealth capabilities - the Harrier had neither.