Performance Of Ground-based Augmentation System Research Articles

Impact of geometry sensitive satellites on the navigation performance of ground-based augmented GPS

This paper discussed the impact of geometry sensitive of satellites on the navigation performance of ground-based augmentation system (GBAS). The nominal number of satellites (space vehicles, or SVs), defined in RTCA/DO-229E, in the global positioning system (GPS) constellation was used in the analysis. In the quantification of GBAS navigation performance (i.e., the protection level or PL computed at aircraft), full constellation and one and two SV outage scenarios were applied through the search process within all combinations of healthy SV geometries (i.e., subsets of SVs in view). It was observed that some SV combinations, subset geometries obtained after depletion of constellation reduced GBAS navigation performances significantly. These geometries were treated as unsafe for an initiation of intended aircraft precision approach and landing. Further, SVs affecting the integrity and the availability of GBAS in this manner were identified as 'geometry sensitive'. The impact of geometry sensitive SVs on the GBAS navigation performance were quantified and ranked per outage cases.

Flight test evaluation of ILS and GBAS performance at Gimpo International Airport

We address the differences in the ways the Instrument Landing System (ILS) and Ground-Based Augmentation System (GBAS) offer approach guidance, and their principles and methods. We perform comparative analysis of the accuracy of deviation between the GBAS Landing System (GLS) and ILS by means of flight tests, using the flight inspection aircraft at Gimpo International Airport. Our results show that the ILS deviation error increases as the distance between the threshold of runway and the aircraft increases; on the other hand, the GLS deviation error is stable, within the range of ±0.5 to ±2 m lateral and vertical deviation, respectively. We also analyze the alignment accuracy of the ILS and GLS based on the evaluation criteria of Category I of the Federal Aviation Administration, and our analysis results confirm that both systems satisfy the requirements (lateral: ±0.1°, vertical: ±0.05°).

GBAS ground monitoring requirements from an airworthiness perspective

The ground-based augmentation system (GBAS) provides corrections for satellite navigation signals together with integrity parameters to aircraft and enables precision approach guidance. It will eventually replace the currently used instrument landing system. GBAS Approach Service Type C stations supporting CAT-I operations have been fully developed and certified, and first stations are operational. For the service type D, which is intended to support CAT-III operations including automatic approaches and landings, requirements have been drafted and are currently undergoing validation. One remaining issue is the requirement for monitoring of ionospheric anomalies in the ground subsystem. Large gradients in the concentration of free electrons in the ionosphere can lead to significant positioning errors when navigation is based on differential methods. We give a review of the derivation of currently proposed performance requirements for such a monitor. Next, we show that the required level of safety from an airworthiness perspective can be achieved even with relaxed monitoring requirements compared to the currently drafted standards. These relaxations result from satellite geometry assessments on the ground and actual approach characteristics toward a runway. We show that with this method, it is sufficient to monitor for gradients in the range of about 450–550 mm/km while current standards require detection already from 300 mm/km. A remote monitoring receiver near the touchdown point can monitor the post-correction differential range error and use it as test statistic for GBAS performance monitoring and protection against ionospheric disturbances.