The U.S. Air Force recently fixed an F-35 maintenance and readiness problem it should not have had. This was all about failing to develop the infrastructure needed to perform scheduled depot-level maintenance or emergency upgrades for the new F135 engines, which were getting their first widespread and heavy use. The air force failed to assemble the skilled personnel, special tools and components needed to carry out the needed depot maintenance on the rapidly expanding fleet of F-35s entering service and flying more hours per aircraft. There were also problems with building enough new F-135 engines to provide the normal stockpile of additional engines to keep F-35s flying. The air force also had a shortage of trained technicians to do the depot level work as well as unexpected shortages in key engine components that wear out or require upgrades to perform reliably.
Lack of skilled manpower, special tools and spare engines is a common problem with nations using new or upgraded jet fighters. It is the reason why the Russian air force was unable to make use of its aircraft superiority (in numbers) over Ukraine in 2022. Many NATO air forces had similar problems after the Cold War ended and aircraft maintenance budgets were cut because keeping the jet fighters in shape to fight a major war was seen as less of a priority with the threat of a major war gone. That proved to be a bad decision because military pilots don’t get as many flight hours as commercial pilots. In airlines you make money keeping the aircraft flying about twelve hours a day carrying passengers or cargo. For air forces it is different and pilots require a certain number of flight hours, which is about 30 percent of that commercial pilots get, to maintain flying and combat skills. Cheaper (per hour) flight simulators do not completely replace actual hours in the air. When an unexpected crisis develops and those combat aircraft are expected to spend more time in the air, flown by skilled pilots, reality asserts itself and the aircraft and pilots cannot perform as expected or for as long as needed.
The F-35 was a new aircraft design that was much more capable than predecessors, which led to a lot of export orders but the manufacturer and air forces then failed to provide the needed resources to carry out routine depot maintenance on engines. Once the engine shortages kept so many F-35s grounded compared to older fighters, the problem was addressed as the air force worked with the manufacturer to get more engines built along with more replacement components and special tools. The engine manufacturer upgraded the engine design to make it more reliable while the air force assigned and trained more skilled personnel to handle the needed number of engines going through depot maintenance without being stalled because of a lack of personnel, parts and special tools. Over the last three years the manufacturer and air force have corrected most of the shortages and engine reliability problems. This led to a 60 percent reduction in the days F135 engines spend completing depot maintenance.
All aircraft engines, especially jet engines, need such periodic maintenance and that requires removal of the engine to carry out the inspections. In some cases this also requires partial disassembly of the engine to reach certain components. Some engine components are known to wear out after a certain number of flight hours and have to be replaced. As additional components are added to the “problem component list” it has to be inspected, which sometimes involves removing other components to get the one you want. These inspections also detect unexpected problems that require a component replacement or the installation of an improved component.
Engines require less frequent inspections and component replacement while still installed in the aircraft. This is called field maintenance because it is performed at the airbase. For commercial transports there are field maintenance facilities at major airports. Field maintenance stocks new engines or refurbished ones back from depot maintenance so aircraft are out of service for a few days to carry out an engine swap and then conduct tests on the newly installed engine before clearing the aircraft for regular service. Commercial airlines have this down to a science because their aircraft spend more time in the air than military combat aircraft do in peacetime. Modern jet fighters are also designed to remain operational during a surge, where each aircraft flies more hours per day, sometimes for several days, to support the need for more aircraft in the air. After a surge the field maintenance teams have to check engines for potential problems. Having the aircraft, pilots and maintainers that can effectively surge is a major combat advantage because many air forces cannot do it as effectively as others. Creating surge-capable aircraft is expensive but for the most capable and expensive fighters, like the F-35, surge capability is essential to justify the high cost of each aircraft.
The American F-35 stealth fighter is very popular with pilots, both American and foreign, who fly it. The manufacturer and the air force were aware of the importance of engine reliability and the ability to provide foreign users with accurate data on resources needed to carry out sufficient field maintenance. The manufacturer was also responsible for determining and providing the required number of replacement engines.
There were other reasons for the F-35 engine problems, and the most critical one was the air force decision to save money by only having one source for the engine, the F135. Early on the air force was urged to heed past experience and spend the extra money to have two engines available. The second engine, the F136, was developed by General Electric and Britain’s Rolls-Royce. Britain was a major export customer for the F-35 and contributed over $2 billion to F-35 development partly because of the Rolls-Royce involvement with the F136. The air force was facing larger problems with the escalating F-35 development costs and in 2007 decided to drop the F136 to help deal with that.
The air force made two other avoidable mistakes; introducing the new ALIS (Autonomic Logistics Information System), a spare parts management system that did not work as expected, and underestimating the difficulty of updating the complex F-35 software in a timely manner. These three bad decisions are now combining to keep F-35 readiness (mission capable) rates low while those for older aircraft, including the F-22 stealth fighter, increase.
The F135 engine got into trouble because the turbine rotor blades were wearing out much faster than expected. Nearly seven percent of the 665 F-35s delivered as of mid-2021 were out of service because of an engine shortage caused by so many engines needing repairs, many because of the turbine rotor blades. There was a fix for the problem; a special coating for the rotor blades that was being applied to engines that came through the maintenance depots for checkups and fixes to any problems found, as well as dealing with rotor blade failure. The engine shortages were the key reason the F-35 readiness fell from 74 percent in 2019 to 52 percent in 2021. The other reasons had to do with continuing problems with ALIS and managing the software update.
There was no simple solution for problems arising from defects in the only engine model available for the F-35. With two suppliers of engines, problems like F135 rotor blades are usually spotted by one of the engine suppliers early and the other engine supplier alerted. The Department of Defense, acting on U.S. Air Force advice, believed that such problems were not going to arise because engine technology had advanced to the point that this was no longer an issue. The air force was wrong.
Additional costs of fixing the readiness problems produced a cost per flight hour of over $35,000. This is substantially more than for the older F-16s and F-15. The F-35 manufacturer earlier said it was possible to reduce F-35 cost per flight hour to about $25,000 by the end of the decade. That is not very convincing because it will cost a lot to achieve that goal, which was supposed to be available early on at much less development cost.
The Department of Defense acceptance of the air force cancellation of the F136 alternative engine program turned out to be a perfect example of "penny wise and pound foolish". By trying to save money needed to develop and field the F136 it could cost our country billions down the road because of the lack of competition, and shrinking the knowledge and manufacturing base required to design and build military jet engines. By 2021 that proved to be correct.