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Pratt and Whitney's F135 engine powers all three variants of the F-35 strike fighter. Air Force photo by Alex R. Lloyd.

Farnborough, UK—After 15 years, Pratt & Whitney is about to complete System Design and Demonstration of the F135 engine, which powers the F-35 family of fighters, company military engines president Bennett Croswell said Tuesday. "Development ends this month … with fewer than [10] issues outstanding after fulfilling 350 propulsion requirements and more than 26,000 components," he said in an interview with Air Force Magazine. "We will continue to support" F-35 flight testing under a separate contract through January, he said. Most of the outstanding issues are "a matter of timing," meaning they can't be closed out until the F135 is assessed "at maturity," which in some cases will be 2020. The required mission readiness rate at that point will be "threshhold 90 percent and goal 94 percent," he said, but the engine is already running at about a mission readiness rate of 95-96 percent, so no trouble is expected even though that criterion will be considered "open" until the maturity point.

The F135 is also supposed to be the same price as the F119 engine, which powers the F-22 fighter and was the basis of the F135, at the 300th engine delivered, even though it's 1,500 pounds heavier and delivers 20 percent more thrust. Croswell said Pratt is on track to make that goal, having delivered 288 F135 engines so far. In Lot 9 and Lot 10, Pratt was able to reduce the F135 cost by 3.4 percent for the conventional take off version and 6.4 percent for the short takeoff/vertical landing version. The company is joining the Lockheed Martin-led "blueprint for affordability" and will invest in further cost reductions through design, process, or materials improvements. The company is also pushing to reduce sustainment costs by tapping the world market and using partner facilities overseas for overhaul and maintenance, Croswell said.