The F-35 Joint Program Office (JPO) said that it is addressing a higher than desired non-mission capable (NMC) rate for maintenance of the Lockheed Martin [LMT] fighter’s F135 engine by RTX‘s [RTX] Pratt & Whitney.
A Government Accountability Office (GAO) report in July last year said that “the F-35 program has not met the 1 percent goal for non-mission capable due to engine maintenance (i.e., the engine is undergoing or awaiting organizational-level maintenance and the aircraft is not able to fly).”
In a Sept. 6 email, the F-35 JPO said that “the overall propulsion system NMC requirement is 6 percent, of which 1 percent is allotted for maintenance down time.”
“As stated in the GAO report, the [F135] NMC for maintenance has been above the 1 percent and is being addressed as part of normal process improvements to the propulsion system,” the F-35 program said.
The July, 2022 GAO report said that Pratt & Whitney officials had said that the 1 percent NMC rate due to engine maintenance goal had not been met “in part because of reliability issues with line replaceable components, which has resulted in the engine needing more maintenance than planned.”
“For example, a speed sensor on the engine has a difficult installation path that often causes damage to the sensor, resulting in an oil leak and replacement of the sensor,” GAO said. “Additionally, the sensor has been difficult to thread into its location, causing damage to the sensor. Therefore, this sensor had been the subject of 33 maintenance malfunction reports, making it a major driver of line replaceable component reliability metrics and increased non-mission capable maintenance rates.”
Yet, the F-35 program said this week that, for U.S. Air Force, Navy, and Marine Corps’ F-35s there have been 29 speed sensor-related maintenance malfunction reports and 20 line replaceable unit (LRU) speed sensor replacements over 465,000 flying hours–rates of .062 and .043, respectively, per 1,000 flying hours.
“Over the thirteen months since the referenced GAO report was published in July, 2022, the F135 NMC rate has averaged 4.1 percent, well below the government’s objective of 6 percent,” Jennifer Latka, Pratt & Whitney’s vice president for the F135 program, wrote in an email from Pratt & Whitney’s press office. “The most recently published F135 NMC rate for June, 2023, was 2.5 percent. Although speed sensors have never been a main driver of F135 maintenance and are not currently, improvements have been implemented.”
The GAO report in July last year said that “none of the three F-35 variants have met their goals” for line replaceable component removals for the F135–a metric gauging the mean flight hours between unscheduled component replacements on F135s installed on the fighters.
“For example, the F-35A has fallen short of its 410 mean flight hour goal by about 60 hours (or 14 percent),” GAO said. “This performance means that line replaceable components are failing more often than desired, requiring them to be removed and replaced by maintainers more frequently than planned.”
The F-35 program said this week that “the LRU information in the GAO report is correct.”
“The Propulsion Management Office continues to improve reliability and maintainability in the system through proven propulsion processes, such as the Component Improvement Program [CIP],” the F-35 JPO said. “We anticipate the newest production [F-35] CTOL (conventional takeoff and landing) and CV (carrier variant) models to meet specifications.”
Between 2020 and 2022, Congress provided about $70 million annually for the overall Air Force engine CIP, which is to devise engineering solutions to ensure flight safety, correct deficiencies and improve readiness. In fiscal 2023, Congress funded Air Force CIP at nearly $97 million. Separately, Congress funded F135 CIP at nearly $40 million in fiscal 2022 and 2023. Since 2021, F135 CIP efforts have included improving the design of the engine’s speed sensor to be more reliable, GAO said.
“Improvements to the reliability and maintainability of the line replaceable components, such as the speed sensor, reduce the number of parts needed to sustain the engine as well as the time for conducting field maintenance,” GAO said in its report in July last year.