While Pratt & Whitney works to incorporate a new approach to engine maintenance across the F-22 fighter fleet, the company is eyeing opportunities to expand the effort to the F-35 and commercial customers, executives told Inside Defense this week.
Known as Usage Based Lifing, the process aims to leverage available full-flight data to more accurately calculate the usage rates of a given engine component, said Julie Ireland, Pratt’s F119 program manager. The process, she said, allows customers like the Air Force to exhaust the full potential of a part, extending time-on-wing rates and reducing overall lifecycle costs.
First announced early last month, the UBL program has already been activated at two F-22 Air Force bases: Nellis AFB, NV, and Langley AFB, VA, Ireland said in a Tuesday interview. The rest of the fleet is expected to follow in the coming months.
Unlike predictive maintenance, in which officials rely on data and proactive measures to project when certain equipment may experience issues, Ireland noted Pratt’s approach is “looking at the actual life consumed” on a part-by-part, life capability basis.
Pratt executives likened the change in approach to new advances in car oil change interval technology; rather than assuming an oil change would be needed after every few thousand miles regardless of how the car is driven, new technology tells drivers the percentage of the oil’s lifetime remaining before replacement is needed.
“Nowadays, the engine parameters will tell you how much life is taken out of the oil so when you finally do change the oil, there’s no life left -- you capture all the value as the driver,” said Tom Prete, engineering vice president of military engines.
A similar philosophy applies to UBL; rather than assuming certain aircraft life-limited parts will need maintenance based on a near-worst-case usage scenario, Scott Ackroyd, F119 chief engineer, explained the company can instead run data from the jet through an algorithm and “actually account for the damage that was done” on a specific flight. That value is then totaled up and applied to the life limit of a part.
That means, Prete said, that those calculations are based on real time information gathered from how a pilot flew the fighter, where it was flown, the number of excursions that were completed and more.
“When you finally pull the engine, it’s because there’s actually no life left, not because you’re having to limit the life to the worst case flight conditions, then you leave a bunch of life that you never reach because you replaced the parts,” he said.
Ireland said because the F-22 engine “was already calculating all those parameters and dumping it,” all executives had to do was create a lifing algorithm to embed in Lockheed Martin’s maintenance system and transition to that new technology. The information, she said, then feeds into the government’s engine management database charged with tracking fielded power modules and their life limits.
From there, Ireland said the data allows the company to forecast expected future damage across the fleet and have parts ready to go for subsequent engine overhauls.
Pratt projects the program will save the Air Force more than $800 million tied to the F119 engine fleet, largely by reducing maintenance in the overhaul shop, which Ireland said is “the biggest driver of costs for any engine program.”
Going forward, company executives plan to send a team out to Elmendorf AFB, AK, in June, to transfer the management system of the fighters there from the earlier lifing technology to the new one before continuing with the rest of the F-22 fleet through the summer and fall.
While Ireland said the original plan had been to head to Eglin AFB, FL, in May, the service’s planned retirement of 33 F-22 Block 20s in its fiscal year 2023 budget request means the base was pushed “to the end of the line, waiting to understand what happens with the potential divestiture.”
If approved by Congress, the move would drop the current fleet of 186 F-22s down to 153. In all, 36 aircraft make up the Block 20 fleet, which are primarily used for training and not currently operationally capable.
“Depending on what happens there, we may or may not change those over,” she said.
Beyond the F-22s, Prete, engineering vice president of military engines, said the company's “plan is absolutely to continue to extend UBL” to other engine models, including commercial and the F135, which is the F-35 Joint Strike Fighter’s engine.
The F119 essentially served as the foundation for the design of the F135, and Prete said many of the algorithms that enable UBL are already in the F135. He added the vision for the F-35 engine is that parts of it “will be under a UBL-type approach” that involves measuring all the life and usage of components within that power module.
Regardless of whether the Air Force opts to move forward with plans to incrementally upgrade the current F135 engine or replace it with advanced engine technology developed through the Air Force’s Adaptive Engine Transition Program, Prete said executives are able to leverage their advanced algorithms through either engine model.
Though Pratt favors the incremental upgrade approach, the company also has developed an XA101 through AETP to fit the F-35A conventional variant -- a program in which General Electric is also involved.
“We’re excited to have options,” Prete said. “Either way, we will be positioned to bring that learning -- things like UBL and the digital thread -- to that engine model.”