The performance, such as coverage and accuracy, of the conventional air navigation systems are about to reach their limits. Therefore, International Civil Aviation Organization (ICAO) has decided to introduce Global Navigation Satellite System (GNSS), such as GPS, etc, as a navigation system, which solely enables the guidance anytime, anywhere in the world, in other words, from oceanic airspace to landing including airport surface. However, in order to use the current GPS and other satellite navigation systems for aviation purpose, their performance, such as reliability, positioning accuracy, etc, must be improved. Satellite Based Augmentation System (SBAS) and Ground Based Augmentation System (GBAS) are designed to satisfy such requirements. The application of GNSS to landing systems enables flexible approach paths with high precision and high reliability, which enables efficient approaches in congested airports and landing into runway without ILS.

    SBAS uses geostationary satellites to broadcast the differential type augmentation information of wide area generated from GPS data collected at the ground monitoring stations located over the wide area. GBAS broadcasts highly accurate and reliable augmentation information to the aircraft around the airport using VHF data broadcast system from the ground station.

    At present, SBAS and GBAS are under development in many countries for use as aircraft landing systems. To put them into practical use in Japan, where ionospheric activity is severe, further improvement of augmentation performance and adequate safety analysis considering actual geographic conditions are indispensable. ENRI is carrying out the researches to improve the performance of SBAS and is conducting a safety analysis of GBAS in order to apply GNSS to landing systems.