Reuters

The second production model F-35A Lightning II aircraft flies above the compass rose of Rogers Dry Lakebed at Edwards Air Force Base, Calif., in this image distributed by the U.S. Air Force dated May 13, 2011.

The Pentagon said on Thursday it would resume flights of its F-35 fighter jets, which were grounded a week ago after a crack was discovered in an engine blade during a routine inspection.

The cautionary flight suspension began on Feb. 21 after a 0.6 inch crack was found on a turbine blade of a test aircraft at the Edwards Air Force Base F-35 Integrated Test Facility.

Comprehensive tests on the blade were later conducted at the Pratt & Whitney facility in Middletown, Conn., where prolonged exposure to high levels of heat and other operational stressors were determined to be the cause of the crack, a statement from the F-35 Joint Program Office read.

No additional cracks were found during inspections of the remaining inventory, the statement added.

It was the second time F-35s have been grounded in recent weeks. The Pentagon grounded its 25 F-35B jets, used by the Marine corps, on Jan. 18 after a fuel line detached during a training flight.

The F-35B — one of three varieties used by the U.S. — was cleared to resume testing two weeks ago.

The Defense Department touts the Joint Strike Fighter — its most expensive military hardware program, at roughly $400 billion — its "next-generation strike aircraft weapon systems," offering "cutting-edge technologies to the battlespace of the future."

Military planners envision the F-35 as taking a lead role in so-called "first day of war" operations, eventually replacing a range of workhorse jets, including the F-16, the A-10 and the F/A-18. Current plans call for the U.S. to buy 2,443 aircraft under a contract with Lockheed Martin.

NBC News' Courtney Kube and M. Alex Johnson contributed to this report.

Related:

Pentagon grounds all F-35 strike fighters over crack in engine blade

U.S. Air Force via Reuters file

The crack was discovered in an engine blade of an F35A at Edwards Air Force Base, Calif..

The Defense Department grounded all 51 of its F-35 Joint Strike Fighters, the U.S. military's most expensive project, after a crack was discovered in an engine blade during a routine inspection, it said Friday.

It's the second time F-35s have been grounded in recent weeks. The Pentagon grounded its 25 F-35B jets, used by the Marine corps, on Jan. 18 after a fuel line detached during a training flight. The F-35B — one of three varieties used by the U.S. — was cleared to resume testing only last week.

Unlike that suspension, the action announced Friday affects all of the U.S. military's F-35s.

The crack was discovered in an engine blade of an Air Force F-35A Edwards Air Force Base, Calif., the Defense Department said in a statement. The engine, manufactured by Pratt & Whitney, was being shipped to the company's facility in Middletown, Conn., for more evaluation, it said.

"It is too early to know the fleet-wide impact of the recent finding," the statement said.

Matthew Bates, a spokesman for Pratt & Whitney, told The Army Times that the engine analysis should take "roughly" a week.

The Defense Department touts the Joint Strike Fighter — its most expensive military hardware program, at roughly $400 billion — its "next-generation strike aircraft weapon systems," offering "cutting-edge technologies to the battlespace of the future."

Military planners envision the F-35 as taking a lead role in "first day of war" operations, eventually replacing a range of workhorse jets, including the F-16, the A-10 and the F/A-18. Current plans call for the U.S. to buy 2,443 aircraft under a contract with Lockheed Martin.

Follow M. Alex Johnson on Twitter and Facebook.

Watch US News videos on NBCNews.com