The U.S. Air Force’s fiscal 2024 budget asks for $245 million for Raytheon Technologies‘ [RTX] F135 Engine Core Upgrade (ECU) for the Lockheed Martin [LMT] F-35 and cancels a new adaptive cycle engine for the fighter, but DoD has yet to determine what power and thermal management system (PTMS) it will use for ECU, according to a new GAO report, F-35 Joint Strike Fighter: More Actions Needed to Explain Cost Growth and Support Engine Modernization Decision (GAO-23-106047).
The F135 will need an improved PTMS, “as bleed air and power extraction to support the current PTMS is nearly double the specification value and is preventing F135 engines from achieving their designed overhaul intervals,” the F-35 Joint Program Office (JPO) said. The F-35 program is holding a PTMS industry day on June 12-14 in Crystal City, Va. “With engine and thermal management modernization on the horizon, DoD, the military services, and Congress are at a critical juncture,” GAO said in the new report. “While the DoD has proposed moving forward with the engine core upgrade, it has not determined what PTMS option it will select and the other power and cooling related components that it will need to modernize.” Honeywell [HON] builds the current PTMS for Raytheon’s Pratt & Whitney F135.
The F-35 program wants to field an enhanced PTMS by 2029 to accommodate dozens of new weapons and sensors in Block 4 aircraft.

GAO has questioned the F-35 program’s Business Case Analysis’ consideration of engine and power and thermal management system options and said that the analysis “did not follow any particular DoD guidance related to business case analysis [BCA] or analysis of alternatives” (Defense Daily, March 29).

GAO’s comments may lend support to lawmakers who want to keep the new adaptive cycle engine option open for the F-35. General Electric [GE] has developed its XA100 adaptive cycle engine under the Air Force’s Advanced Engine Transition Program (AETP), while Pratt & Whitney developed a counterpart, XA101, under AETP.

The new GAO report advised DoD to perform further analysis.

“Completing the additional analysis typically included in business case analyses would provide DoD, service leaders, and Congress with better information as they continue to make decisions related to engine and thermal management modernization,” GAO said. “Without this type of information on technical risk, technology maturity, and costs, the military services may risk warfighters receiving less capability than anticipated while taking more time and resources than the military services can afford.”
Late deliveries of the F135 have been a significant problem, per GAO.
“In 2022, the engine contractor—Pratt & Whitney—delivered four of 127 F135 engines on time even with multiyear efforts to address this long-standing issue,” the report said. “Since 2017, Pratt & Whitney has continually faced challenges delivering engines on time…Program officials attributed late engine deliveries over the past year to quality issues and contractor supply chain challenges, among other things. We previously reported that DoD requested that Pratt & Whitney address issues with late deliveries and quality control. In response, the contractor submitted a corrective action plan and implemented steps to enhance delivery performance. DoD agreed and accepted the corrective action plan in September 2022, but late deliveries persist.”
Last December, Lockheed Martin and Pratt & Whitney halted deliveries of the F-35 and the F135 engine after the pilot of a Lockheed Martin-owned F-35B ejected on the runway at Naval Air Station Joint Reserve Base Fort Worth, Texas on Dec. 15. Lockheed Martin said that it resumed flight acceptance testing on March 6 after a fleetwide retrofit to mitigate engine harmonic resonance–higher than normal engine vibration–that the program cited in a low number of fighters with relatively new F135s (Defense Daily, March 6).
The F-35 program had maintained a so-called “engine buffer”–a standing supply of F135 engines at government warehouses–to ameliorate the late engine deliveries, but the new GAO report said that last December’s delivery pause eliminated that buffer.
“As of February 2023…the program reported there is no longer a buffer, but officials are working on a recovery plan,” GAO said. “Specifically, after an F-35B crashed in December 2022, program officials stated that they implemented an engine delivery pause while DoD and the contractors could identify the root cause of the accident. Due to this pause in deliveries and the use of the engines that had remained in the buffer to support sustainment needs and the production line, there is no longer a buffer of engines. According to DoD officials, while engine deliveries resumed in mid-February 2023, program officials stated that they are still working through a recovery plan to restore the buffer and ensure Pratt & Whitney delivers engines on time.”

The new report also touched upon F-35 deliveries.

“In 2022, Lockheed Martin delivered 50 percent of aircraft late, which represents the highest level of late deliveries over the past 6 years and three times worse than the percentage in 2021,” GAO said. “According to program officials, these late deliveries were, in part, due to longstanding supply chain issues. We found in April 2022 that the program office modified the contracted delivery date for aircraft scheduled for delivery in 2020 through 2023. The program moved delivery dates for some of these aircraft to later dates to help Lockheed Martin and the production line recover from issues with ongoing supply chain challenges exacerbated by the COVID-19 pandemic. As a result, some aircraft initially considered late were determined to be on time. Regardless of this relief, Lockheed Martin is continuing to deliver aircraft late in part due to ongoing manufacturing issues and parts shortages, which were exacerbated by the COVID-19 pandemic, according to contractor representatives.”

In addition, GAO said that parts shortages “increased significantly in 2022, and Lockheed Martin is taking steps to address late parts that affect the production line.”

The modified delivery schedule established by the F-35 program “reduced parts shortages to the production line by 79 percent in 2021,” GAO said. “During the fall of 2021, the weekly average of parts shortages was down to 11 parts at its lowest. However, as of December 2022, the weekly average of parts shortages increased to 169, the highest they have been since the contract modification.”