AIRPASS was a British aircraft interception radar and fire-control radar system developed by Ferranti. It was the world's first airborne monopulse radar system and fed data to the world's first head-up display. The name is an acronym for "Aircraft Interception Radar and Pilot's Attack Sight System". In the Royal Air Force (RAF) it was given the official name Radar, Aircraft Interception, Mark 23, normally shortened to AI.23.[1] AIRPASS was used on the English Electric Lightning throughout its lifetime.
The basic AIRPASS electronics system was later adapted as the basis for a terrain-following radar for navigation and targeting for air-to-ground attacks. This AIRPASS II was originally intended for the BAC TSR.2, but when that aircraft was cancelled in 1965, it was subsequently used in the Blackburn Buccaneer. Elements of the AIRPASS design were used on many subsequent radars from Ferranti, while its head-up display was licensed for use in the United States, where it was quickly adopted for many aircraft.