GBAS

GBAS, or Ground-Based Augmentation System, is an aviation navigation aid that enhances GNSS signals to support precision approach and landing operations around an airport. It provides differential corrections for satellite orbit and clock errors, atmospheric delays, and a robust integrity monitor, enabling a GPS/GNSS-based landing system (GBAS Landing System, GLS).

Operational concept: A GBAS ground facility, containing multiple GNSS receivers and a processor, tracks GNSS signals and generates real-time corrections and integrity data. This information is transmitted to aircraft in the approach area via a dedicated VHF data link. Equipped aircraft apply the corrections to construct a precise navigation solution and guidance path to the runway, delivering lateral and vertical guidance comparable to ILS—often termed GLS.

Capabilities and scope: GBAS supports precision approaches with vertical guidance, typically Cat I and above, with the potential for multiple approaches for different runway ends within the coverage area, usually a few kilometers from the airport. It is designed as an alternative to ILS and complements satellite-based augmentation systems such as SBAS.

Regulatory and deployment context: GBAS was developed under ICAO standards and is described in Annex 10 and PANS-OPS; installations are becoming common at major airports worldwide. The FAA's LAAS is a related system in the United States; while similar in purpose, it uses a slightly different broadcast approach.

Limitations and considerations: GBAS depends on GNSS availability and integrity, and can be affected by GNSS outages, ionospheric activity, and radio-frequency interference. Airborne GBAS receivers and ground equipment must be certified to meet rigorous performance and integrity requirements.