Defence conglomerate Raytheon has conducted laboratory tests on a new power and cooling system for the Lockheed Martin F-35 fighter jet, which the company says can more-than-double the capacity of the current Honeywell power and thermal management system (PTMS).

Raytheon subsidiary Collins Aerospace is developing the Enhanced Power and Cooling System (EPACS), which is intended to support the planned Block 4 suite of upgrades to the F-35.

F-35 germany

Source: US Air Force photos by Airman 1st Class Jovante Johnson and Airman 1st Class Valerie Seelye |

US Air Force F-35As taxi on the flight line at Spangdahlem Air Base, Germany in 2019. While the Pentagon is planning an engine upgrade for its F-35 fleet, government auditors say the advanced jets will also need a more capable power and cooling system

Speaking at the 2023 Paris air show in Le Bourget, Collins’ president of power and controls Henry Brooks says based on initial test results, EPACS will provide more than twice the cooling capacity of the F-35’s Honeywell PTMS.

“This development can really carry improvements for the F-35,” Brooks says. “That is expected to support the cooling needs for the remainder of the F-35 life cycle.”

The F-35 PTMS works in tandem with the jet’s single Pratt & Whitney (P&W) F135 engine. Siphoning so-called bleed air from the engine, the PTMS provides electrical power and cooling to the fighter’s radar and advanced sensor package.

However, as capability improvements have been made to those systems since the jet’s debut, the onboard power and cooling requirements have grown. That requires diverting additional bleed air to the PTMS, reducing engine performance and increasing degradation.

While P&W maintains the F135 can operate under such conditions, it comes at the cost of longevity. A recent report from auditors at the US Government Accountability Office (GAO) found overtaxing the F-35’s engine has racked up $38 billion in extra maintenance costs.

“It’s operating beyond two times the specification of what it was originally operating at,” Jill Albertelli, P&W president of military engines, says of the F135.

The cooling problem will soon become even worse, as Lockheed and the Pentagon prepare to launch the Block 4 series of upgrades – a modernisation package of some 50 improvements that will dramatically expand the F-35’s power and cooling needs.

“[The engine] could keep going supporting Block 4,” Albertelli says. “But it will bring a maintenance cost, that I would say the US and the partner countries in the services across NATO would not want to see.”

Currently, P&W is focused on delivering an engine core upgrade (ECU) package for the F135 that will address the short-term cooling and engine degradation issue ahead of the Block 4 rollout.

However, the recent GAO report found the Pentagon will need to develop a plan for upgrading the current Honeywell PTMS to support any F-35 capability improvements beyond Block 4.

“All of that requires a different level of level of cooling than we’ve seen before,” Brooks notes.

While the Pentagon has not yet established a formal programme for addressing the shortcomings of the F-35 PTMS, Collins and Raytheon are positioning the EPACS as the successor to the current Honeywell system.

Just as P&W is building the ECU to be a so-called “drop in system” requiring no structural modification to be compatible with all three F-35 variants, Collins has a similar goal for EPACS.

Albertelli says P&W will be ready to start installing ECU packages in 2028.