Ranking U.S. Air Force officers delivered a robust defense of the F-35 Lightning II on September 20, even as a limited number of A-model fighters remained grounded because of a fuel-tank insulation problem while others on the assembly line must be fixed. The service and manufacturer Lockheed Martin plan to repair the 15 grounded fighters by December.

“I’m hopeful that as we continue to grow this fleet, we all take the opportunity to form opinions on this airplane from experts, and the only experts in the F-35 business are those that fix, maintain and fly the F-35 on a day-to-day basis,” Brig. Gen. Scott Pleus, director of the Air Force F-35 Integration Office, told the Air Force Association Air, Space and Cyber conference in National Harbor, Md. “If you are forming your opinions by somebody who has not fixed or flown the airplane, I would tell you you’re wrong. I’m here to tell you that this aircraft is performing very well and getting better each and every day.”

On September 16, the Air Force suspended the flight operations of 15 operational F-35As, including two Norwegian air force fighters currently stationed at Luke Air Force in Arizona, after inspections revealed that insulating material around avionics coolant lines was eroding into the wing fuel tanks. The problem also affects 42 A-model fighters on Lockheed Martin’s assembly line in Fort Worth, Texas, the service found. Marine Corps’ F-35Bs and Navy F-35Cs are not affected.

“The most recent issue that we’re dealing with right now is not a technical issue, it is not a design issue, it is a quality escape from a supplier,” Lt. Gen. Christopher Bogdan, program executive officer with the Pentagon’s F-35 Joint Program Office (JPO), told the conference. The JPO, Lockheed Martin, the Air Force Life Cycle Management Center and the Naval Air Systems Command “have come up with an engineering solution in which we will go in by cutting holes in the wings—and there are access panels we can go through also—and remove that insulation and FOD [foreign object damage)] and close the airplane up and allow it to get back into flight.”

The Air Force was in the process of writing a maintenance procedure for the fix, Bogdan said, and Lockheed Martin has assembled eight teams to begin repairing the fielded jets in the next two weeks. The service expects that effort will take until December to complete.

“Our first priority is the 15 airplanes in the field and then we will work our way back to resolving the 42 airplanes on the production line,” Bogdan said. “We will spend most of October and November ‘modding’ those airplanes and getting them back into a flyable condition and then we will work on the production airplanes.”

Pleus moved from flying the F-16 Fighting Falcon to the F-35 in 2015 as wing commander at Luke AFB. Seated behind an F-35 helmet-mounted display system, he predicted the Lightning II will exceed all other fighters in performance once it receives its Block 3F full mission systems software release.

“Once we get to 3F software and full warfighting capability on this airplane, I’m confident it’s going to deliver an awesome combat capability,” Pleus said. “In terms of lethality and survivability, the aircraft is absolutely head and shoulders above our legacy fleet of fighters currently fielded.”