Colonel Kevin Killea, who oversees aviation requirements for the Marine Corps, said the decision would allow officials to quickly resume flight tests of the F-35B, the Marines' version of the new warplane being built by Lockheed Martin Corp.

But he said the Navy and the F-35 program office had more work to do to resolve the manufacturing issues blamed for the grounding.

The Pentagon and the Navy grounded all 25 F-35B jets on Jan. 18 after a fuel line made by Stratoflex, a unit of Parker Hannifin Corp, detached just before a training flight in Florida on Jan. 16. The Pentagon later said the issue stemmed from a manufacturing defect, not maintenance or design issues.

Joe DellaVedova, spokesman for the Pentagon's F-35 program office, said all 25 F-35 B-model warplanes were cleared for flight as soon as any defective fuel lines had been replaced.  He said all the affected hoses had been inspected and those found to have problems would be replaced. The hose in question is part of the exhaust system on the F-35B, which can take off from short runways and land like a helicopter.

Stratoflex is a subcontractor to Britain's Rolls Royce Plc , but the prime contractor for the F-35B engine is Pratt & Whitney, a unit of United Technologies Corp.

Resumption of test and training flights of the F-35B is good news for the $396 billion F-35 program, which must complete an aggressive schedule of test flights this year to keep the program on track after earlier delays.

The Pentagon's F-35 program office lifted the flight restrictions on nine developmental test F-35B aircraft, and Vice Admiral David Dunaway, head of Naval Air Systems Command, followed suit later by approving flights by 16 additional F-35B jets that are being used for training, defense officials said.

Flights of the Air Force's A-model and the Navy's C-model of the F-35 were unaffected because they do not have the same fuel line involved in the incident that triggered the grounding.

Lockheed is building three variants of the F-35 for the United States and eight countries that funded its development: Britain, Canada, Australia, Norway, Denmark, Italy, Turkey and the Netherlands. Israel and Japan are also buying the planes.

Besides the Marine Corps, Britain and Italy also plan to buy the F-35B.

All the aircraft will have to undergo an initial checkout flight before they can resume testing or training flights, said a defense official who was not authorized to speak publicly.

The official said it was unclear how the grounding would impact the overall test program for the F-35B since that model had been a bit ahead of schedule with flights before the grounding. "There will be some impact for sure. Thirty days of testing is 30 days," said the official.

The Pentagon continues to analyze equipment made by Stratoflex and remains in discussions with Pratt & Whitney about the cost of the detailed inspections and repairs, the official said.

So far, 82 hoses from the F-35B aircraft have been shipped to an independent company in Minnesota for CT scans. Initial analysis showed 10 of 36 hoses were overcrimped and needed repairs, said the official, adding that five sets of hoses had been cleared for use.

Pentagon and Navy officials have adjusted the requirements for the hoses after studying the performance of a test engine, being used by Pratt & Whitney, that was found to have an overcrimped hose but logged 1,600 hours of use without a problem.