On Monday, August 24, 2026, US corporation RTX announced that its Collins Aerospace subsidiary had completed altitude testing of the new EPACS (Enhanced Power and Cooling System) for Lockheed Martin F-35 Lightning II family multirole combat aircraft.
Photo: RTX
EPACS, designed to improve power and thermal management as a successor to Honeywell’s current PTMS (Power and Thermal Management System), will provide significantly increased cooling capacity to meet current and future requirements. By providing the critical thermal margin needed to support planned technology upgrades, EPACS will ensure that the F-35 remains at the forefront of performance throughout its service life.
“Successful altitude testing validates system performance in real-world flight conditions,” says Ira Grimmett, vice president, Environmental & Airframe Control Systems for Power & Controls at Collins Aerospace. “Completing this phase of testing advances EPACS maturity and reinforces confidence in the system’s capability and performance.”
Altitude testing is a key element of early development and risk reduction for the new PTMS. The system was tested over several days at power levels reflecting mission requirements. It was pushed to the limits of its operating envelope at various altitudes to collect performance data and demonstrate that EPACS can provide the expected emergency power during operation. The testing also validated the system’s performance models.
This latest milestone follows Collins Aerospace’s February 28, 2025 announcement that EPACS had met aircraft integration requirements. Earlier, on June 30, 2024, the company reported that a prototype of the system had demonstrated 80 kW of cooling capacity. The first laboratory tests were announced on June 19, 2023.
EPACS is part of the ongoing modernization of the F-35. It is directly linked to the Pratt & Whitney F135 turbofan engines through the auxiliary power unit (APU). In March 2025, the F135 fleet surpassed one million flight hours. At the time, engine readiness was reported at 94%. The engines are now undergoing the ECU (Engine Core Upgrade) modernization, intended to improve durability and performance and enable full use of F-35 aircraft in the latest Block 4 configuration with Technical Refresh 3 (TR3), as well as support further capability growth across all three F-35 variants worldwide. The upgrade package will also be applied to Polish F-35A Husarz aircraft. Meanwhile, on March 30 this year, the US Department of Defense awarded RTX a contract worth 3,813,591,875 USD for production of another batch of F135-PW-100/400/600 engines.
#NEWS: Collins Aerospace completed altitude testing of its Enhanced Power and Cooling System (EPACS), a next-generation Power and Thermal Management System. Designed for the F-35, EPACS delivers increased cooling capacity to support planned upgrades. More: https://t.co/ifGHCPqpaT pic.twitter.com/Ei2k9Zs9TM
— RTX (@RTX_News) August 24, 2026
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