ABSTRACTAn interferometric GPS flight reference system (IGPS FRS) has been implemented and flight tested on a transport category aircraft. The underlying principle of operation is similar to that used for kinematic surveying, and is also referred to as differential carrier‐phase tracking. The objectives of the IGPS FRS include 0.1 m accuracy RMS (each axis); one or more updates per second; UTC time synchronization better than 0.1 ms; real‐time, all‐weather operation; and repeatable flight paths. The latter requirement calls for full aircraft integration and coupled flight.This paper discusses the IGPS FRS architecture, its principles of operation, the aircraft integration, and the initial static calibration and flight test performance results. These are the first reported results for an interferometric GPS flight reference/autoland system that resolves carrier‐phase ambiguities in flight while simultaneously providing high‐precision guidance to a transport category aircraft through direct coupling to its flight contro