The F-35 Joint Program Office (JPO) considers the planned Engine Core Upgrade for the Raytheon Technologies‘ [RTX] Pratt & Whitney F135 engine and a new or upgraded Power and Thermal Management System (PTMS) as a single effort.

Honeywell [HON] builds the PTMS as a subcontractor to Lockheed Martin [LMT], the F-35 prime. The PTMS uses air pressure from the engine to cool aircraft subsystems and enables main engine start, emergency power, cockpit conditioning, equipment cooling, and some electrical power.

A new Government Accountability Office (GAO) report says that the F135 will need a new or improved PTMS to accomodate future weapons and sensors on the aircraft (Defense Daily, May 30). The question appears to be when.

The report said that the F135’s cooling system “is overtasked, requiring the engine to operate beyond its design parameters” and that “the extra heat is increasing the wear on the engine, reducing its life, and adding $38 billion in maintenance costs.”

“There are multiple PTMS options under review; selection will be based on the requirements specified by the services,” the F-35 JPO said on May 31. “The modernization effort (both ECU and PTMS) is expected to be fielded in the early 2030 timeframe.  We are in the early design phase and the schedule is dependent upon the approved solution.”

The F-35 program is to hold a PTMS industry day in Crystal City, Va., on June 12-14.

“The JPO is already very confident we can minimize the $38 billion impact simply with ECU,” the F-35 program said on May 31. “The ECU will restore engine life, and the PTMS solution will ensure that the air vehicle can support future capability growth. We are treating the ECU and PTMS as a single modernization effort because they must be designed together to work with the greatest efficiency.”

The F-35 program has said that 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.”

Jen Latka, Pratt & Whitney’s vice president for F135 programs, told reporters in a virtual forum on May 31 that the F135 ECU “alone could fully enable Block 4.”

“We just know that there are capabilities beyond Block 4, but to get to that point you’re gonna have to do something to PTMS too,” she said. “An engine alone, whether you upgrade it or put a new engine in, doesn’t do it.”

The GAO report, however, calls into question whether the F135 ECU will provide enough cooling to accomodate Block 4 or whether the F135 ECU will need a new or upgraded PTMS as well to allow Block 4

“Modernization capabilities—including Block 4 capabilities already installed and future ones planned for through 2035—require even more cooling capacity and air pressure than the PTMS and the engine can support, respectively,” the study said. “Program officials noted that Lockheed Martin did not anticipate needing more cooling from the PTMS when it proposed Block 4. However, the addition of Block 4 will require more cooling capacity.”

The GAO report said that the F-35 program “determined that it must upgrade the PTMS by 2029 to enable capabilities planned through 2035 and upgrade the engine to reduce life-cycle costs.”

The study said that, 15 years ago, Lockheed Martin discovered that the Honeywell PTMS would need more air pressure from the F135 to cool F-35 subsystems and that, “in 2013, Lockheed Martin requested to change the F135’s design to provide more air pressure to the PTMS, but program officials determined that it was too late to redesign the engine given the cost and schedule effects of such a change at that stage of the overall program.”

“Program officials decided to continue with the F135 engine’s original design with the understanding that there would be increased wear and tear, more maintenance, and reduced life on the engine because it would need to provide more air pressure to the PTMS than its design intended,” the report said.