LONDON - The likely cause of the F-35A engine fire June 23 that eventually resulted in a fleetwide grounding is excessive rubbing between the turbine blades and the cowling, says Frank Kendall, Pentagon procurement chief.

Inspections of other F-35 engines indicate the problem is not endemic to the fleet, he told reporters during a July 13 roundtable here prior to the Farnborough air show, which starts tomorrow. Pratt & Whitney makes the F135 engine; Lockheed Martin leads the airframe team for the F-35.

“The evidence we have so far - we do not see at this point what I call a systemic problem,” Kendall said. “We understand to a degree what happened here. The question is why did it happen.”

The rubbing between the blades in the low-pressure turbine and the cowl surrounding them put increased stress on the blades; one failed catastrophically, prompting an engine fire. The pilot safely egressed and investigators have sequestered the aircraft for review.

A limited degree of this rubbing is expected and acceptable, Kendall said, but in this case it far exceeded expectations.

Pratt & Whitney spokesman Matthew Bates declined to provide any further detail pending the investigation.

The fire prompted local commanders to each put flights on a safety hold, followed by a full “red stripe” grounding for the entire F-35A, B and C fleet issued July 3 by the Navy. That remains in effect as air worthiness authorities in the Air Force and Navy review data to assess when the single-engine, stealthy jets can fly again. Meanwhile, the U.K. jet BK-3 remains at Eglin AFB, Florida, awaiting that decision before it can fly to join three Marine Corps F-35Bs at Naval Air Station Patuxent River, Maryland. They were slated to make the historic Atlantic Ocean crossing as early as two weeks ago for a flying display at the Royal International Air Tattoo last week and Farnborough this week. It is unclear whether they will make it to Farnborough.

“Before we put the airplane in the air, we’d like to know exactly what happened and why,” Kendall said.