The Pentagon grounded the global fleet of F-35 stealth fighters Thursday so that engineers could conduct urgent inspections following the first ever crash of the costliest plane in history.
Preliminary data from a Marine Corps F-35B that was completely destroyed in a South Carolina crash last month showed a potential problem with a fuel tube, officials said.
"The US services and international partners have temporarily suspended F-35 flight operations while the enterprise conducts a fleet-wide inspection of a fuel tube within the engine on all F-35 aircraft," said Joe DellaVedova, a spokesman for the F-35 program.
He added that suspect fuel tubes would be removed and replaced. If good tubes are already installed, then those planes will be returned to operational status.
Inspections were expected to be completed within 24 to 48 hours.
According to Pentagon figures, 320 F-35s have been delivered globally, mainly to the US but also Israel and Britain, as well as other partner countries.
Britain said the Pentagon measure did not affect all of its F-35s, and that some flying missions had been "paused," not grounded.
"F-35 flight trials from the aircraft carrier HMS Queen Elizabeth are continuing and the program remains on schedule to provide our armed forces with a game-changing capability," a British defense ministry spokesman said.
The Israeli military said it was taking additional precautions and conducting tests on its version of the F-35, known as the F-35I.
But if the planes are "required for operational action, the F-35I aircraft are ready and prepared," a statement read.
On September 28, a Marine Corps F-35 crashed in South Carolina. The pilot survived after ejecting.
The incident occurred only one day after the US military first used the F-35 in combat, when Marine Corps jets hit Taliban targets in Afghanistan.
On Wednesday, Defense News reported that Defense Secretary Jim Mattis had ordered the Air Force and Navy to make 80 percent of the fleet of key fighters, including the F-35, mission capable within a year.
The order sent ripples through the Pentagon, where officials have for years bemoaned a general lack of readiness for key equipment.
Launched in the early 1990s, the F-35 program is considered the most expensive weapons system in US history, with an estimated cost of some $400 billion and a goal to produce 2,500 aircraft in the coming years.
Once servicing and maintenance costs for the F-35 are factored in over the aircraft's lifespan through 2070, overall program costs are expected to rise to $1.5 trillion.
Proponents tout the F-35's radar-dodging stealth technology, supersonic speeds, close air support capabilities, airborne agility and a massive array of sensors giving pilots unparalleled access to information.
But the program has faced numerous delays, cost overruns and setbacks, including a mysterious engine fire in 2014 that led commanders to temporarily ground the planes.