HILL AIR FORCE BASE, Utah — The U.S. Air Force says it has grounded most of its F-35 Joint Strike Fighter fleet due to concerns over ejector seat safety.

Air Combat Command, the parent command over Hill Air Force Base, confirmed they have grounded F-35s at HAFB to “expedite the inspection process.”

“ACC’s F-35s have Martin-Baker ejection seats, and on July 19, began a Time Compliance Technical Directive to inspect all of the cartridges on the ejection seat within 90 days,” Air Force officials said. “Out of an abundance of caution, ACC units will execute a stand-down on July 29 to expedite the inspection process. Based on data gathered from those inspections, ACC will make a determination to resume operations.”

#BreakingNews: U.S. F-35 fleet GROUNDED due to safety concern – basically the entire fleet at HAFB. Tune in to @KSL5TV at noon with what we've learned from Air Force officials. pic.twitter.com/TelSUqfKj8

— Braden McElreath (@BradenKSL) July 29, 2022

The inspections come after the Navy and Marine Corps began replacing ejection seat parts in some fixed-wing aircraft after manufacturer Martin-Baker discovered a defect.

According to Business Insider, Martin-Baker first identified the potential defect in the cartridge actuated devices, or CADs, which are involved in the deployment of the parachute when pilots pull the ejection handle.

“Since CADs are used in the ejection process, a faulty CAD may not allow all the functions necessary to take place that would allow a complete and safe ejection,” Michael Cisek, a senior associate at the aviation consulting firm AeroDynamic Advisory, told Breaking Defense on Wednesday. “While the aircraft are flyable, I don’t think too many pilots would be willing to fly knowing they may not be able [to] eject.”

F-35s, which arrived at HAFB in 2015, currently make up the majority of aircraft at the base.

Nearly 300 trainer aircraft have also been grounded in Florida.