The Pentagon said in a statement Thursday that the U.S. military and its international partners, which have also purchased F-35 fighter jets from contractor Lockheed Martin, would be suspending flight operations to inspect the fuel tubes out of caution.

“If suspect fuel tubes are installed, the part will be removed and replaced,” the Pentagon said in a statement. “If known good fuel tubes are already installed, then those aircraft will be returned to flight status. Inspections are expected to be completed within the next 24 to 48 hours.”

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The engines in question are made by aerospace manufacturer Pratt & Whitney, a secondary contractor on the F-35. “We’re fully supporting our customers in helping them to identify the problem parts and come up with a proper solution for replacement,” said John Thomas, a company spokesman.

By the end of the day on Thursday, the U.S. military and some foreign partners had already put planes back into service without the suspect fuel tube back. Only planes with a fuel tube from a certain supplier require replacement, and so far officials believe that number is limited to about half the roughly 340 aircraft in service.

According to the Pentagon, the decision to temporarily suspend operations for the fleet is the result of initial data that investigators gathered in their probe of last month’s crash.

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During the incident, a Marine Corps variant of the F-35 joint strike fighter, known as the F-35B, went down in the vicinity of Marine Corps Air Station Beaufort. The pilot ejected safely.

The accident marked the first crash of an F-35 in the 17 years since Lockheed Martin won the competition for the fighter jet in October 2001 and teamed up with other contractors to begin production of the high-profile plane.

The fighter jet has experienced other issues over the years, including concerns about pilots receiving enough oxygen while flying and engine fires on the ground. But last month’s incident was the first time the plane had crashed.

“The primary goal following any mishap is the prevention of future incidents,” the Pentagon statement added. “We will take every measure to ensure safe operations while we deliver, sustain and modernize the F-35 for the warfighter and our defense partners.”

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The United States and other nations that have bought the joint strike fighter are flying more than 340 of the jets but plan to purchase thousands of the planes in the coming years.

The F-35 has attracted attention not only for its capabilities but also for its cost, after delays and overruns helped make the fighter jet program the most expensive in the Pentagon’s history.

Last month, the Pentagon said the latest batch of F-35s would cost the military $89 million per unit for the most common variant, the first time the plane’s price tag had dropped below $90 million. The more complex Navy and Marine Corps variants remained above $100 million.

The fighter jet’s high cost attracted President Trump’s attention in the month before he entered office and prompted him to suggest that he would scrap the plane in favor of a different one from Boeing. The military, however, has stuck with production of the joint strike fighter.