F-35 engine upgrade clears key design review, Pratt says

NATIONAL HARBOR, Md. — An upgrade for the F-35 stealth fighter’s engine has passed a crucial design review, teeing up the program to move into subsequent testing and eventually production, according to a top executive at manufacturer Pratt & Whitney.

“It means that we’ve been working integration work with the airframe. It means that the design is solid. It means that we’re ready to move forward from an industrial base as well,” Jill Albertelli, president of Pratt’s military engines business, said of the design review in an interview with Breaking Defense on Monday. (Today, Pratt’s parent company RTX announced that Albertelli has been promoted to serve as Pratt’s president, effective Jan. 1, 2027.)

The enhancement, known as the Engine Core Upgrade (ECU) for the stealth fighter’s F135 powerplant, specifically passed what’s known as a risk reduction design review. Albertelli explained on the sidelines of the Air and Space Forces Association conference here that the milestone is essentially the same as a critical design review — Pentagon parlance for analysis that confirms a system design will perform as expected, among other criteria. 

About one-third of unique hardware for the first engine to test in the upgrade program is “in process,” Albertelli said. 

Among the next steps is the first engine test, according to Albertelli. She declined to comment directly on when specific milestones are planned and referred questions to the F-35 Joint Program Office. A top Air Force official, however, previously told reporters that ground testing will kick off in 2027, followed by flight testing around 2030. 

When Pratt pushed the ECU plan several years ago, officials projected the program could be ready to enter service by 2028. But according to a review by the Government Accountability Office last year, ECU production isn’t slated to begin until 2031. 

Asked about Pratt’s assumptions for fielding ECU, Albertelli said, “We always want to make sure we are giving the customer what they’re prioritizing,” noting as well that “funding isn’t unlimited, so we have to balance those equations on what the need is.” Pratt, she emphasized, is “meeting [the government’s] milestones.” 

Military officials say the engine program will deliver greater thrust and fuel efficiency. The upgrade is also meant to restore expected engine life and support a suite of forthcoming upgrades known as Block 4. 

The engine upgrade — which officials selected after passing over a whole new, so-called “adaptive” propulsion system for the F-35 — will save “tens of billions” of dollars in maintenance costs compared to foregoing an enhancement for the F135, Albertelli said. 

All three variants of the F-35 are expected to benefit from the ECU, which is planned to be retrofitted into existing jets. The Pentagon recently awarded a roughly $240.8 million modification for ECU work, following a $1.3 billion base contract issued in September 2024.