A U.S. Air Force F-35 flies in afterburner thrust during an air show in Toronto in September 2022.

A U.S. Air Force F-35 flies in afterburner thrust during an air show in Toronto in September 2022. Rick Madonik/Toronto Star via Getty Images

Overheating F-35s May Get Service-Specific Cooling Upgrades, Likely Hiking Cost

The jets’ engines are running twice as hot as designed, boosting maintenance and capping performance.

Each of the three U.S. services that fly the F-35 can choose a bespoke cooling fix for their overheating planes, likely making the Joint Strike Fighter a bit less joint and a bit more expensive.

The Air Force, Navy, and Marine Corps may draft their own requirements for the cooling upgrade for the jets, whose Pratt & Whitney F135 engine is running twice as hot as designed, requiring earlier and more frequent maintenance, according to the F-35 Joint Program Office, or JPO.

The jet relies on a power and thermal management system, or PTMS, that pulls air from the engine to cool its radar and other electronic systems. But planemaker Lockheed Martin discovered in 2008 that cooling requires more “bleed air” than anticipated. 

Pentagon officials have hired Pratt for a long-planned engine upgrade, but they haven’t yet specified the cooling requirements—in part because each of the services may need different amounts. 

“The services will provide their cooling requirements to support their desired capabilities. They understand the risk associated with a unique PTMS solution, and that commonality is paramount to controlling costs, which is a key tenant of the F-35 program,” JPO spokesperson Russ Goemaere said in a statement Friday. 

If the services choose different paths, it could boost sustainment costs, according to a new Government Accountability Office report.

“We have a firm handle on engine and power thermal management system options that are needed for future cooling needs, based on the services’ requirements,” Goemaere said. 

GAO also estimated the cost of forgoing upgrades to the plane: $38 billion.

Since Pratt’s upgrade would eliminate the need for additional maintenance, “my guess is it would translate to eliminating all of those costs,” Jen Latka, vice president of Pratt’s F135 program, told reporters on Wednesday. Latka added that she couldn’t definitively say whether the engine core upgrade, or ECU, would bring $38 billion down to zero because she’s not privy to how GAO came to that figure.

But she said Pratt wants a decision on a solution for the cooling system “soon” so that they can “optimize” their engine design for that solution.

“We want to be designing the engine core upgrade in parallel with whatever decision is made or whatever changes are made to the PTMS solution,” she said. 

Latka also said an upgrade to the cooling system will be needed to power whatever new capabilities are added to the F-35 after the currently planned Block 4 addition of electronic warfare and other systems.

“There are capabilities that [they] want to come on to the jet beyond Block 4, and so to get to that point, you're going to have to do something to PTMS too. An engine alone—whether you upgrade it or put a new engine in—doesn't do it.”

Knowing when the jet will need these upgrades is “more of an art than science,” Latka said, because Pratt doesn’t exactly know when future technology will be needed on the jet. 

It’s “really important” to note that the JPO doesn’t have a plan for Block 4 “out to 2035,” Latka said. “They have increments of capabilities that are funded in the next few years that are coming on to the jet. And then they have some more thought-out ideas, let's say, of what could come on to the jet in the next set of years. And then there are dreams of what we could put on the jet way into the future.”

Latka couldn’t comment on just how DOD will want to update the cooling system, but said that the JPO is looking at everything from a clean-sheet design to various upgrades to the existing Honeywell system.

JPO’s Goemaere said, “The modernization effort (both ECU and PTMS) is expected to be fielded in the early 2030 timeframe. We are in the early design phase and the schedule is dependent upon the approved solution.”

The office has been working on an acquisition plan for the jet’s upgrades and expects that to be approved later this summer, Goemaere said. The plan will be deemed “controlled unclassified information,” and program officials do not plan to post a “comprehensive unclassified summary of the acquisition strategy. We do plan to provide an unclassified public statement with basic information about the strategy once it is approved,” he said. 

Latka said that Tuesday’s GAO report “actually validates” the Pentagon’s decision to pursue an upgrade for the existing F135, rather than a new, adaptive engine. The upgrade is “low-risk” because the engine is already in the plane, and the adaptive engine wouldn’t work across all three variants of the F-35, Latka said. 

Latka also denied GAO’s contention that the program has emptied its stockpiles of engines it delivers when the production line isn’t running fast enough. After an F-35B crashed in December and engine deliveries were paused because the Pentagon found a vibration in the F135 engine, GAO said the program’s “buffer” of engines was gone. 

However, Latka said, “Never once did Lockheed Martin's production line reach and pull for a ready-for-install engine and not have one. Never once did that occur—so it did not impact Lockheed’s production line the way it was kind of stated in the report.” 

After Pratt validated a fix for the engine, the company was able to get the delayed engines back to the warehouse, Latka said, where the stockpile resides.  

“All of the engines that we had been building in January and February, we delivered. So it's not an issue. We're back to having the same buffer,” she said.