F-35 F135 Engine Hits 1 Million Hours, but Challenges Loom Large
On March 3, U.S. aircraft engine manufacturer Pratt & Whitney announced that the F135 engine had passed the 1 million flight hours marker. The F135, a derivative of the F-22A’s F119 engine, has been the sole power plant for the F-35 Lightning II fighter aircraft since that program’s inception.
Pratt & Whitney boasted in a press release that this milestone is proof that the F135 “has established itself as the safest, most capable and reliable fighter engine, delivering superior performance and advanced low-observable technologies for the fifth-generation fighter.”
“The engine has powered every F-35 since the fighter’s first flight in 2006, providing exceptional safety and readiness rates,” Jill Albertelli, president of Military Engines at Pratt & Whitney, stated in the press release. “Accomplishing this milestone in under two decades demonstrates how critical the F-35 remains and highlights Pratt & Whitney’s commitment to our customer and the warfighter.”
More than 1,300 of the engines have been produced since the program began, with Pratt & Whitney claiming a full mission capability rate of 94 percent.
“The F135 engine plays a critical role in maintaining global air superiority for the U.S. and its allies, as it enables the F-35 mission in even the most contested environments,” said Albertelli.
F-35: Struggling With Upgrades
But in recent years, repeated upgrades of the F-35 have increased the performance requirements placed on the F-135 engine.
Upgrades have been implemented in steps as part of the Block 4 modernization program, which was initiated as a response to the many new threats to the aircraft that have emerged in the two decades since its original requirements were defined.
Flight trials and operational data from the aircraft in service have revealed how the Block 4 upgrade has placed significant demands on the F135 engine. Specifically, the aircraft now requires more power for its on-board systems, as well as more cooling than original design parameters were measured for.
Modernization needs, and the fact that the F135 is derivative of a late-1980s design, have combined to produce a situation in which the engine is overworked. Because of this, the Department of Defense has authorized funding to modernize the engine.
Among the funding line items, the DoD authorized $497 million for an F135 engine core upgrade (ECU) as part of the defense appropriations bill for Fiscal Year 2024.
According to repeated concerns expressed by the U.S. Government Accountability Office in two reports published in 2023, the Block 4 upgrade for the entire F-35, including the ECU, was supposed to be completed in 2026 at an estimated cost of $10.6 billion—but the cost of the upgrade increased to $16.5 billion, and it is now estimated that it will not be completed until 2029.
The Legacy of the F-22
Aviation specialists familiar with the history of the F135’s development reach back to the engine’s genesis during the competitive flight trials of the YF-22 and YF-23 to explain today’s shortcomings.
Back then, the Pratt & Whitney F119 was selected over the General Electric F120 engine by the U.S. Air Force.
This was not because the F119 was superior in performance, but because it was considered to be a lower-risk design than the more technologically sophisticated GE engine.
This was considered a smart choice at the time. But in the years since, it has become obvious that the less advanced design of the Pratt & Whitney engine, which became the basis for the F-135, has been a less than ideal match for the F-35.
“These engine problems for the F-35 program are only going to increase with time,” said one former DoD official who is very familiar with aircraft.
“The F135 engine is the product of a competition in which there was never a true ‘fifth-generation’ engine that was the winner,” he explained.
“So, we are running a supposedly a fifth-generation program with a substandard engine – almost like a repeat of the mistakes that were made on the B-29 program back in World War II.
“Until the [F135] engine receives a real upgrade—or even better is replaced by a completely new engine—the aircraft is going to suffer with the availability rates and other reliability problems that keep increasing all the time.”
About the Author: Reuben F. Johnson
Reuben F. Johnson is a survivor of the February 2022 Russian invasion of Ukraine and is now an Expert on Foreign Military Affairs with the Fundacja im. Kazimierza Pułaskiego in Warsaw. He has been a consultant to the Pentagon, several NATO governments and the Australian government in the fields of defense technology and weapon systems design. Over the past 30 years he has resided in and reported from Russia, Ukraine, Poland, Brazil, the People’s Republic of China and Australia.
