Environmental control system improvements planned for a radar equipped AV-8B aircraft are presented. The aircraft, designated the Harrier II Plus, is a joint venture by McDonnell Aircraft Company and British Aerospace Corporation with the USMC and several foreign customers in mind. The principle aircraft change is the addition of the AN/APG-65 multi-mode radar. This radar, along with other Harrier II Plus cooling requirements, imposes a nine-fold increase in the aircraft's avionics cooling requirement. Extensive changes to the aircraft's two environmental control systems resulted and are presented herein. Topics covered include: 1) Current AV-8B ECS configuration, 2) Harrier II Plus design requirements, 3) Bleed circuit changes, 4) Heat sinks, 5) ECS packages, 6) Avionics cooling control, 7) Liquid cooling system, and 8) Ground cooling provisions. The changes identified will increase the aircraft's cooling capacity from 12 kw to 21 kw.