Fifteen Percent Of U.S. Air Force F-35s Don’t Have Working Engines

Marine Corps, Navy, and foreign F-35s are also being impacted by ongoing problems with the jets’ engines.

byThomas Newdick|
F-35 photo


A total of 46 F-35 stealth fighters are currently without functioning engines due to an ongoing problem with the heat-protective coating on their turbine rotor blades becoming worn out faster than was expected. With the engine maintenance center now facing a backlog on repair work, frontline F-35 fleets have been hit, with the U.S. Air Force’s fleet facing the most significant availability shortfall.

At a hearing before the U.S. House Committee on Armed Services’ Subcommittee on Tactical Air and Land Forces yesterday, Air Force Lieutenant General Eric T. Fick, director of the F-35 Joint Program Office, confirmed that 41 U.S. Air Force F-35s, as well as one Joint Strike Fighter belonging to the U.S. Marine Corps, another from the U.S. Navy, and three that had been delivered to foreign air forces were grounded without engines. Those figures were as of July 8. 

An F-35A assigned to the 61st Fighter Squadron at Luke Air Force Base, Arizona, takes off as the sun sets, during corrosion testing of the F135 engine., U.S. Air Force/Staff Sgt. Staci Miller

The exact breakdown of how many of each F-35 variant lack engines is unclear. The Air Force and the Navy only fly the F-35A and F-35C, respectively, but the Marines operate both F-35Bs and F-35Cs and various models are in service with other military forces around the world.

With regards to the Air Force specifically, as of May 8 this year, the service had received 283 F-35As, which means that around a little under 15 percent of the service’s Joint Strike Fighters can’t be flown due to this engine shortage.

"They had a rush on the depot due to unexpected Calcium-Magnesium-Alumino-Silicate (CMAS) degradation on deployed F-35As," Steve Trimble, Aviation Week’s Defense Editor and a friend of The War Zone, wrote on Twitter. "And the depot itself has been a bottleneck, with turn times at two-times planned rates earlier this year.”

The depot in question is the F135 Heavy Maintenance Center at Tinker Air Force Base, Oklahoma, which looks after the F-35’s turbofan engines, which are produced by Pratt & Whitney. The Heavy Maintenance Center is the primary repair depot for all F135 engines, including those operated by the Navy and Marine Corps units, and some of the foreign partners in the F-35 program.

While Trimble noted that those depot rates “are coming down now,” this is not good news for a program that has suffered its fair share of setbacks in recent months, with criticism of its operating costs, in particular, extending all the way to the top of the Air Force.

It’s also noteworthy that this particular engine problem has been rumbling on for some time now. Shortages of F135 powerplants were reported back in February when it emerged that the Tinker Air Force Base facility was unable to complete scheduled depot maintenance on the engines as quickly as required.

The ribbon-cutting ceremony for the F135 Engine Heavy Maintenance Center at Tinker Air Force Base in 2014. , U.S. Air Force/Kelly White

Contributing to the backlog was the discovery of “premature distress of rotor blade coatings,” Defense News

reported at the time, meaning the depot was having to add unscheduled engine repairs to its worklist. Back then, an unnamed defense official confirmed to the same publication that the worn-out blades had led to a “serious readiness problem.”

That problem now seems to have gotten worse. As of February, it was predicted that 5-6 percent of the F-35 fleet might be left without engines by 2022, providing that planned fixes worked as hoped. If they didn’t, the same official told Defense News, then the figure could leap to 20 percent of Air Force F-35s being grounded.

The figures for last May suggest that while the effects of a fix may now be in kicking in, to some degree, the number of F-35s without engines is worse than was projected.

Prior to the details of the turbine rotor blades emerging, senior Pentagon officials were concerned that issues with the F-35’s engines were impacting mission capable rates — one of the metrics used to gauge how many of the Air Force’s aircraft are actually ready to conduct their assigned mission at any one time.

One of the results of those engine problems was the decision to reduce the number of air show appearances scheduled for the F-35A Demonstration Team, which is provided by the 388th Fighter Wing at Hill Air Force Base, Utah. That measure was hoped to reduce the burden on the engine depot.

Captain Kristin Wolfe, F-35 Lightning II Demonstration Team commander and pilot, performs at the 2020 Fort Lauderdale Air Show last November., U.S. Air Force/Capt. Kip Sumner

Exactly when it became apparent that the work needed to address the CMAS blade coatings — coupled with the slower progress on F135 scheduled depot maintenance — is unclear. However, even in early 2020, the Pentagon had publicly flagged an engine shortage issue.

A second shift should have been introduced at the F135 Heavy Maintenance Center last month, Defense News reported, which should help mitigate the problem as the depot seeks to bring reduce the time it takes to process an engine from over 200 days to around 122 days.

For its part, Pratt & Whitney said it introduced a hardware modification to the engine blades last year and that the same treatment is being made to engines as they pass through the overhaul process.

It is worth remembering too, of course, that the F-35 enterprise almost had an alternative engine to the F135. However, the General Electric/Rolls-Royce F136 turbofan was deemed to be an unnecessary expense and was eventually canceled in 2011, when the project was over 80 percent complete. With the benefit of hindsight, it can well be imagined that an alternative source of engines would be very valuable right now.

A General Electric/Rolls-Royce F136 engine, the alternate powerplant for the F-35 Lightning II Joint Strike Fighter, is tested at maximum thrust conditions., Rick Goodfriend

While the engine issues regarding the F135 may well prove to be more temporary in nature, the latest revelation does come amid growing concerns about the sustainment costs associated with these jets, more generally. There were also reports about F135 cost growth as a result of Turkey being ejected from the Joint Strike Fighter program, although this hasn’t been linked in any way to the maintenance issues currently ongoing.

Looking further ahead, there is the potential to upgrade the powerplant for the F-35 as part of the long-term roadmap for the jet. An adaptive-cycle engine, designed to modulate the airflow, improving fuel efficiency, and boosting range, is one of the options. Pratt & Whitney and General Electric are both working on designs under the Air Force Research Laboratory’s Adaptive Engine Transition Program, or AETP. In the shorter term, technology that emerges from AETP could end up providing the basis for an F135 upgrade, too.

Meanwhile, in an event that seems unlikely to have been entirely coincidental, the F-35A Demonstration Team on May 25 paid a visit to Tinker Air Force Base “as a show of appreciation for the men and women who perform depot-level maintenance on the F-35’s engine and related components,” in the words of an Air Force press release.

Members of the Oklahoma City Air Logistics Complex Heavy Maintenance Center pose for a group photo with the Air Force’s F-35A Demonstration Team during their visit to Tinker Air Force Base, Oklahoma, on May 25, 2021., U.S. Air Force/Paul Shirk

“The commander of Air Combat Command [General Mark Kelly] said he wanted to do something to motivate the forces that are powering the F-35,” said Brigadier General Jeff King, Oklahoma City Air Logistics Complex commander, at the time.

Among the other items on show on the maintenance side were “new, more advanced, borescopes, a flexible camera used to inspect internal engine components.”

After the flight demonstration, F-35 Demo pilot Major Kristin “Beo” Wolfe said: “We would not be combat-ready without all the hard work of the F135 engine team.”

With that in mind, it must be hoped that the efforts that have been taken to smooth the process of engine maintenance, and fix the problem of excess wear and tear on turbine rotor blades, will finally address the engine backlog and put those 46 F-35s back on a combat-ready status.

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