The F-35A that caught fire June 23 was a recent delivery from low-rate initial production lot 5 of the stealthy fighter.

Ninety-five F-35s have been delivered to date.

All F-35s remain barred from flight operations as investigators continue to explore the cause of the fire in the aft end of an F-35A as it prepared for takeoff at Eglin AFB, Florida.

Some test aircraft were flying as of June 25 at Edwards AFB, California, and NAS Patuxent River, Maryland, says Kyra Hawn, a program spokeswoman. But as of June 26, flights are suspended for safety reasons. Some test assets, however, have been cleared for ground use at the test centers.

The single-engine aircraft are in a "cautionary suspension of flight," Hawn says. Lockheed Martin manufactures the F-35, which costs nearly $100 million apiece.

A determination has not yet been made on the cost of the damage to the aircraft that caught fire, but it is likely to be the first F-35 class A mishap. A class A mishap occurs when an aircraft sustains more than $2 million in damage or results in a fatality; in this case the pilot safely egressed before foam was used to extinguish the fire. But the fire is thought to have badly damaged the Pratt & Whitney F135 engine.

No military airworthiness authority has yet issued a grounding order. Decisions to stand-down flight are being made by local commanders, according to military officials.

"Safety of our personnel, community, and aircraft are our key concern in all flight-test operations. Following the June 23 F-35A incident, some local operators opted to temporarily suspend F-35B and C operations as a precaution," says Lt. Jackie Pau, a Navy spokeswoman. "The [Marine and Navy] airworthiness authorities are awaiting initial assessment results from the investigating authorities to enable decision-making with regards to flight operations of F-35B and C. This initial assessment and subsequent decision by the airworthiness authorities will not compromise the safety/mishap investigation proceedings."

Likewise, the U.S. Air Force has now suspended all F-35A flying operations; wing commanders previously issued the order to halt flights. "The wing commander temporarily suspended flying operations, while Air Education and Training Command initiated a safety investigation. As a precautionary measure, the Air Force has decided to temporarily suspend all F-35A operations until it is determined that flights can resume safely," says Maj. Natasha Waggoner, an Air Force spokeswoman. "This is not an uncommon practice following a mishap. It ensures the safety of our crews and our aircraft so we can determine there is no fleet-wide issue that needs to be addressed."

Hawn says the halt to flight operations is still not expected to impede the Marine Corps’ ability to launch four F-35Bs from Patuxent River in advance of their international debut at the Royal International Air Tattoo outside London the week of July 7. However, officials are keeping an eye on storms predicted in the North Atlantic Ocean this weekend that could delay the launch by 24 hr.

Editor's Note: This article incorrectly stated the Class A mishap damage cost threshold. It was updated in 2009 to be $2 million.