National Harbor, Md. —  The 15 operational F-35A joint strike fighters grounded by a recent fuel line issue will likely be fixed and able to fly again by the end of the year, the program's director said today.

However, the program office is still assessing how long it will take for a group of 42 jets, in various stages of production, to be repaired — among them the first two Israeli F-35A models, scheduled for delivery in December.

Lt. Gen. Chris Bogdan, the head of the F-35 Joint Program Office, said at the Air Force Association's annual conference that contractor Lockheed Martin is preparing to test a potential fix on a ground-test aircraft next week. If that fix works, Lockheed will send a set of eight teams out to the field the following week to start repairing the jets.

Click here for our coverage of the 2016 Air Force Association conference. 

Thirteen F-35A models used by the US Air Force, as well as two for the Norwegian Air Force, were grounded last week due to the coolant line issue. The design of the plane has the coolant lines traveling through where fuel is stored, although only on the outer tip of the wing. The insulation placed around that coolant line to keep it from being affected by the warm fuel was found to be decomposing into the fuel.

The issue was limited to the A models and does not impact the Marine Corps' F-35B model or the Navy's F-35C models.

The solution involves cutting holes in the wings of the jets and removing the bad insulation, as well as cleaning out the potential damage from those pieces floating around. Bogdan downplayed the challenge of cutting into the wing despite the stealthy coating and composite design of the plane, saying there are a number of access panels near the entry point that can also be used.

The Pentagon is working with the supplier to correct the issue, and plans to continue using the supplier in the future because of the number of jets expected to come online in the coming years. And Lockheed will be covering the costs, something Bogdan emphasized to reporters.

"To Lockheed’s credit — write this down, this is important — to Lockheed’s credit, at the highest levels of the corporation, they have committed to doing the right thing, and the definition of doing the right thing is they will pay for all of the engineering and all of the modification for all 52 airplane," Bogdan said.

The general also hit at those who would characterize the insulation issue as part of the long history of issues that have cropped up with the joint strike fighter, saying this was "not a technical issue, it is not a design issue. It is a quality escape from a supplier that supplied us with installation."

International Production Impact

In addition to the operational jets, there are 42 production models which had the flawed lines installed. While getting the operational jets up and flying again is the priority, the JPO plans to start working on those repairs as quickly as possible.

Jets for Italy, Japan, Norway and. perhaps most critically, Israeli planes — including the first two F-35As that the Israeli government expects to have delivered to them in December — are affected.

Those two Israeli jets are the priority fix among the production models, Bogdan said, adding that the JPO still expects to deliver those planes on time. However, he could not give a timeline for when the production models would e fixed, in part because the planes are in various states of assembly.

"Some of them just had their wings put on. Some of them, the wings aren’t even on there yet. So the procedure for fixing those airplanes runs the gauntlet from virtually very little to having to cut holes in wings," Bogdan said. "So we’ll take care of fielded airplanes first, and then the production airplanes."

Given that the Israeli jets are so close to being handed over, it is likely they will require the more intensive fixes of the production jets.

As to the operational jets, Bogdan said Lockheed and the JPO is working on an assessment of the danger for the operational jets to fly, and left open the possibility those jets could begin flying again before the fixes are in if the risk is found to be negligible.