The Pentagon’s F-35 program is facing new delays in the delivery of its Pratt & Whitney engines, a revelation that comes just days after a major new F-35 production contract was finalized with Lockheed Martin.
According to the F-35 Joint Program Office (JPO), contracts for Lots 18 and 19 of the Pratt & Whitney F135 engine will not be finalized until spring 2026, about six months later than planned. The JPO confirmed the revised schedule in a statement to Air & Space Forces Magazine. The change affects hundreds of engines destined for the next batch of F-35s ordered by the US and allied customers.
The F135 is built by Pratt & Whitney, a subsidiary of RTX. It powers all three versions of the F-35: the conventional F-35A, the short-takeoff and vertical-landing F-35B, and the carrier-capable F-35C.
The delay follows last week’s announcement that the Pentagon and Lockheed Martin had finalized a $24.3 billion contract for 296 F-35s, split between production Lots 18 and 19. Deliveries for that order are expected to begin in 2026 at Lockheed’s assembly line in Fort Worth, Texas.
The JPO hasn’t said if the engine delays will slow down F-35 deliveries. But since Pratt & Whitney builds the engines and then ships them to Lockheed for installation, any delays in engine deliveries could end up delaying the final aircraft.
Supply chain strain
A recent report from the US Government Accountability Office found that all 123 F135 engines delivered in 2024 arrived behind schedule, with an average delay of 238 days. The watchdog also raised concerns about the incentive-fee structure that allows Pratt & Whitney to receive partial performance payments even when deadlines are missed.
Pratt & Whitney has struggled with production and maintenance capacity as demand for the F-35 grows. The company is also developing a major Engine Core Upgrade (ECU), intended to extend engine life and provide additional power for advanced onboard systems in future F-35 variants. The ECU effort has itself been delayed, with the company recently missing its critical design review milestone.
RTX, Pratt & Whitney’s parent company, has cited ongoing supply-chain pressures, cost inflation, and workforce shortages across its commercial and defense divisions. The company is also managing a major recall in its geared turbofan engine program used on commercial airliners, which has strained its manufacturing network.
The JPO has not reported any safety or design defect in the F135. The delays seem to be caused by production slowdowns and parts shortages, not by a problem with the engine’s design. The engine has powered the F-35 since its first flight in 2006 and has accumulated more than 1.7 million flight hours.
In June, the Pentagon reaffirmed its decision to continue with Pratt & Whitney’s F135 rather than switch to a new adaptive-cycle design proposed by GE Aerospace. Lawmakers decided it would be less costly and disruptive to improve the current engine instead of starting over with a new engine.
Program pressure
The F-35 Lightning II remains the largest and most complex weapons program ever undertaken by the US Department of Defense. The lifetime cost, including procurement and sustainment, now exceeds $1.7 trillion. More than 1,230 aircraft have been delivered to date to the U.S. and 19 allied nations.
The new $24 billion order aims to keep production steady through the end of the decade, but engine bottlenecks could complicate those plans. The JPO said it is working closely with Pratt & Whitney “to maintain alignment of aircraft and engine deliveries.”
