Steve Trimble Pratt & Whitney expects a multiyear recovery from a growing engine availability crisis that has grounded dozens of F-35As.
Steve Trimble
F135 engines continue to roll off Pratt & Whitney assembly lines as the shortage deepens. Credit: Pratt & Whitney
A shortage of Pratt & Whitney F135 engines that is already keeping more than four dozen Lockheed Martin F-35s grounded will continue to worsen. The year-old crisis has driven some lawmakers to call for replacing the F135 with an advanced new engine. And the bad news comes as the F135 program is within a year of a costly, first wave of scheduled, 2,000-hr. repair cycles.
But the road to a long recovery begins with a first step, and Pratt executives can point to a clear sign of progress: The only F135 Heavy Maintenance Center opened so far, in Oklahoma, has reduced turnaround times by more than half, to 120 days for each of the last “few” engines, says Jen Latka, Pratt’s vice president for the F135 program. A year after producing only 14 power modules, the depot is on track to deliver 45-50 this year, up to 25% more than forecast.
“They’ve just had a tremendous amount of progress this year,” Latka says.
The improved turnaround times are necessary but still insufficient. The F-35 engine shortage is the result of a complicated puzzle that includes the discovery of a critical design flaw, chronic underinvestment in global depot capacity, an early breakdown at the F-35’s only repair facility, an overreliance on a global spares pool and even laws restricting how the government pays for engines.
In a twist of fate and legal logic, the F-35’s engine shortage comes as the program experiences an unprecedented and growing surplus of production F135 engines. The Joint Program Office buys F-35 airframes and engines separately. Although Lockheed has adopted a “production smoothing” plan to defer dozens of planned annual aircraft deliveries due to the prolonged impact from COVID-19 pandemic-related supply chain shortages, Pratt continues to deliver engines according to the original delivery plan, Latka says.
As a result, 40-60 surplus production engines will pile up in warehouses over the next several years, even as operational F-35As remain grounded for lack of spares. If the Defense Department were a commercial airline, most of the engine shortage could be solved in the near-term by redirecting production engines to the spares pool. But budget laws prohibit the department from transferring engines paid for with production funding to serve as spares, which must be paid for with sustainment funding.
The shortage is partly due to a Pratt design mistake. The company had expected that a new coating applied to the turbine blades would improve resistance to corrosion, but deployments of the F-35A to the sand-flecked airspace in the Persian Gulf exposed a critical flaw. The “improved” coating degrades faster in such environments. A new coating adopted in the spring of 2020 has now been applied in about 25% of the engines and has been exposed to the same sandy conditions.
“It’s still early, but we are seeing the performance we expect with that coating design,” says Katherine Knapp Carney, Pratt’s F135 program chief engineer.
But the original coating flaw resulted in a wave of engines being sent to the depot for unscheduled repairs, starting at the end of 2019. The demand quickly overwhelmed the newly opened facility, which in many cases still lacked the technical data needed to make the repairs. The 120-day interval for each F135 now at the Heavy Maintenance Center means the program has hit a steady-state goal, so now the emphasis is on expanding capacity. Another work shift is being added at the existing center, and new F135 engine depots will be opened over the next few years.
Another factor in the engine shortage is a chronic lack of spares. In Pratt’s other fighter engine programs, customers typically allocate 25-30% of all engines to spares, Latka says. The ratio for the F135 program is 11%. The lower sparing ratio appears to have been partly driven by an optimistic forecast of savings from the use of a global spares pool. All F135 spares are shared among F-35 operators.
But Pratt has recommended that the Joint Program Office adopt a more conservative sparing ratio for the next several years, as early operational deployments expose the F135 to new environments and the repair depot capacity remains limited, Latka says. The message seems to have been heard. Earlier this year, the U.S. Air Force submitted an unfunded request to Congress for 20 more F135 power modules to use as spares.
