COMBINED GPS GLONASS LAAS FLIGHT TRIALS

The use of GPS in aviation is now accepted, with extensive work being undertaken on the technological, precision and infrastructure requirem ents. Work has focused on providing a service that is able to operate continuously in all areas. GPS alone, however, is seen as being unable to satisfy the stringent requirements for some phases of flight. Of t he many solutions proposed, the Russian GLONASS system has been regula rly overlooked. The research described in this paper aims to present G LONASS as a realistic and proven augmentation to CPS for aircraft posi tioning. During October 1996 the Civil Aviation Authority (CAA) Instit ute of Satellite Navigation (ISN) at the University of Leeds, in conju nction with the National Air Traffic Services Ltd (NATS UK) and the De fence Evaluation and Research Agency (DERA), performed a series of lan dmark differential GPS/GLONASS flight tests using the DERA BAC 1-11 fl ying laboratory. A real-time differential system was constructed using two GPS/GLONASS receivers developed by the ISN and a C-band data link for the RTCA corrections. Integration onboard the aircraft with avion ic sensors and flight management systems was achieved using the ARINC 429 protocol. Routes were designed and flown to evaluate the complete system over a variety of airborne dynamics for both en-route and appro ach situations. In total, over 16 h of flying time was recorded, inclu ding 30 runway approaches over nine flights. A thorough evaluation of the accuracy and integrity of the positioning system was performed. Em phasis was made in comparing the flight statistics with recognized Req uired Navigation Performance (RNP) figures. The paper describes in det ail the project development and the results achieved. An analysis of t he results, showing that aircraft positioning with GPS/GLONASS augment ation in a local area augmentation system (LAAS) scenario can achieve accuracies that are both comparable with GPS-alone solutions and can s atisfy up to CAT II precision approach criteria, is presented. Results are also given for position propagation using velocities derived from GPS and GLONASS carrier phase measurements. (C) 1997 John Wiley & Son s, Ltd.