An overview of GBAS integrity monitoring with a focus on ionospheric spatial anomalies

Abstract

The Local Area Augmentation System (LAAS) or, more generally, the Ground Based Augmentation System (GBAS), has been developed over the past decade to meet the accuracy, integrity, continuity and availability needs of civil aviation users. The GBAS utilizes a single reference station (with multiple GNSS receivers and antennas) within an airport and provides differential corrections via VHF data broadcast (VDB) within a 50-km region around that airport. This paper provides an overview of GBAS integrity verification, explaining how integrity risk is allocated to various potential safety threats and how monitors are used to meet these allocations. In order to illustrate GBAS integrity monitoring in detail, this paper examines the potential threat of ionospheric spatial anomalies (e.g., during ionospheric “storms”) to GBAS and how GBAS protects users against this threat. In practice, the need to mitigate potential ionospheric anomalies is what dictates CAT I GBAS availability.