The Navy and Air Force have grounded the entire fleet of F-35 Joint Strike Fighters because they don't know the cause of an engine fire that occurred on June 23.
"The root cause of the incident remains under investigation," Rear Admiral John Kirby, the Pentagon's chief spokesman, said in a statement. "Additional inspections of F-35 engines have been ordered, and return to flight will be determined based on inspection results and analysis of engineering data."
A U.S. Air Force pilot safely escaped from an F-35 fighter jet after it caught fire during takeoff on June 23 at Eglin Air Force Base in Florida.
The pilot, who wasn't identified, was preparing to conduct a routine training mission around 9:15 a.m., but aborted the exercise due to a fire in the back end of the Lockheed Martin Corp.-made F-35A Lightning II, according to a statement from the service.
The pilot was able to shut down the engine and escape from the plane unharmed. Emergency responders extinguished the fire with foam. The test plane was assigned to the 33rd Fighter Wing, which trains F-35 pilots for U.S. and international forces.
"We take all ground emergencies seriously," Navy Capt. Paul Haas, vice commander of the 33rd Fighter Wing, said in the statement. "In this case, the pilot followed the appropriate procedures which allowed for the safe abort of the mission, engine shutdown, and egress."
He added, "We have a robust and extensive training program in which every pilot and aircraft crew member is trained, in order to respond quickly and correctly in the event emergencies occur."
What caused the fire, where exactly it originated or how badly it damaged the aircraft, which cost more than $100 million apiece remains unknown.
The F-35 Joint Strike Fighter Program is the Defense Department's most expensive weapons acquisition program, estimated to cost almost $400 billion for a total of 2,457 aircraft for the Air Force, Navy and Marine Corps.
Developmental problems have kept the planes from flying in the past. Last year, the entire fleet was grounded after a crack was found on an engine turbine blade. More recently, test flights were reportedly stopped due to an engine valve fitting.
Operational flights of the aircraft are scheduled to begin next year. The Marine Corps' version of the jet, called the F-35B, which can take off like a helicopter and fly like a plane, is set to reach the milestone by December 2015; the Air Force's by December 2016 and the Navy's by February 2019.
The aircraft was scheduled to perform at the upcoming Farnborough Air Show in England as a way to convince the international buyers that the program was on-track, however that plan is now in jeopardy.
"Preparations continue for F-35 participation in international air shows in the United Kingdom, however a final decision will come early next week," Kirby said.