ABSTRACTAttitude determination using GPS carrier phase has been applied successfully to aircraft in experiments by a number of researchers. In an effort to formally characterize its accuracy and bandwidth performance, a GPS attitude determination system was flight tested against an inertial navigation unit (INU). Based on completely separate physical principles, this testing provides an independent means of evaluating overall performance.For the flight experiments, a twin‐engine turboprop transport aircraft was outfitted with a specially designed attitude determination receiver. A strapdown ring laser gyro INU was operated in the main cabin as the independent reference. For system evaluation, a number of test maneuvers were executed, including pitch angles to ± 30 deg and bank angles to ± 60 deg. Performance in moderate turbulence was measured. The impact of structural flexure during aircraft maneuvering was evalua