The United States Air Force has temporarily halted some US operations due to concerns over defects in pilot eject systems on three well-known US military aircraft.

Pilot seat of an F-35

Alexi Worley, a spokeswoman for the Air Force’s Air Combat Command, said the halt is over concern that explosive cartridges in the F-35, T-38, and T-6 aircraft will not propel the seat from the plane properly during an emergency.

US Air Force F-35

US Air Force T-38

Worley said “On July 19, we began a Time Compliance Technical Directive to inspect all of the cartridges on the ejection seat within 90 days. Out of an abundance of caution, air combat command 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.”

The Air Force says that it suspects ” approximately 203 T-38 and 76 T-6 aircraft may be affected by this issue.” Those numbers represent roughly 40% of the US Air Forces T-38 fleet and 15% of the T-6 fleet.

The Air Force held off disclosing how many F-35s could be affected by the issue. Martin-Baker, the company that manufactures the ejection seats in the three aircraft, has declined to comment.