Pratt & Whitney completes design review for F135 engine core upgrade

Pratt & Whitney has completed the Risk Reduction Design Review for the Engine Core Upgrade of the F135 engine that powers the F-35, parent company RTX said on Sep. 15, 2026. The review, announced by the engine maker, validates the maturity of the upgrade design before the program moves toward production.

The ECU is meant to supply the extra electrical power and cooling that the F-35's Block 4 hardware will need. Those upgrades span a new radar, displays, sensors, avionics and advanced computing equipment. RTX said the review covered detailed design elements, propulsion technologies, integration considerations and risk-reduction work, which it described as necessary to deliver full engine life and the added power and thermal management capacity the Block 4 systems require.

The assessment looked at whether the ECU can meet those power and cooling demands across all three variants of the F-35 Lightning II. According to RTX, the design keeps a high degree of commonality with the existing F135 architecture and is intended as a drop-in upgrade for newly built and already fielded aircraft, with retrofit work to be carried out at F135 depot facilities.

Earlier material from Pratt & Whitney and Collins said that pairing the ECU with the EPACS power-and-cooling system could yield a 7% increase in range and thrust and double the available cooling capacity. RTX characterized the design review as a major program milestone that confirms the maturity of the ECU design and moves the effort closer to production.