What is GLS in Aviation? (Gbas Landing System)

The GBAS Landing System, also known as GLS (Ground-Based Augmentation System for Global Navigation Satellite System Landing System), is an advanced navigational aid used in aviation to provide precise guidance during the approach and landing phases of an aircraft. It enhances the accuracy and integrity of the existing satellite-based navigation systems, such as GPS (Global Positioning System) or GNSS (Global Navigation Satellite System), by augmenting their signals with ground-based components.

The GBAS Landing System utilizes a network of ground-based reference stations, a VHF (Very High-Frequency) data broadcast system, and specialized receivers installed on aircraft to provide real-time corrections and improved navigation information to the flight crew. By transmitting correction messages to the aircraft, the system compensates for errors introduced by atmospheric conditions, satellite orbit inaccuracies, and other factors that can affect the accuracy of satellite-based navigation.

How Does the GBAS Landing System Work?

The GBAS Landing System works by receiving signals from multiple satellites in space through onboard antennas installed on an aircraft. These signals are then processed by the onboard receivers to determine the aircraft’s position, velocity, and attitude. However, due to various factors, including signal degradation caused by atmospheric conditions or satellite orbit inaccuracies, the accuracy of the position information obtained solely from satellite-based navigation systems can be limited.

To enhance the accuracy and reliability of the navigation information, the GBAS Landing System uses a network of reference stations located on the ground. These reference stations receive the same satellite signals as the aircraft but with known positions. By comparing the received signals with the known positions, the reference stations calculate correction parameters that can be used to enhance the accuracy of the satellite-based navigation in real-time.

The calculated correction parameters are then transmitted from the reference stations to the aircraft through a VHF data broadcast system. This system utilizes a ground-based transmitter to broadcast the correction messages over a specific frequency. The onboard receivers installed on the aircraft receive these correction messages and apply them to the satellite navigation measurements, thereby improving the accuracy of the aircraft’s position, velocity, and attitude calculations.

The GBAS Landing System also provides integrity monitoring, which is essential for the safety of aircraft operations. In case the system detects any anomalies or discrepancies in the navigation data, it can alert the flight crew with appropriate warnings and indications. This ensures that any potential inaccuracies or hazards are identified, allowing the crew to take appropriate corrective actions and maintain a safe flight path.

Advantages of the GBAS Landing System

The GBAS Landing System offers several advantages over traditional satellite-based navigation systems:

1. Increased Precision

By incorporating ground-based corrections, the GBAS Landing System significantly enhances the precision of aircraft navigation during approach and landing. It can provide position accuracy of less than one meter, enabling pilots to fly more precise flight paths and execute smoother landings. This level of precision is especially crucial for airports with challenging terrain or in adverse weather conditions where precision approaches are required.

According to the Federal Aviation Administration (FAA), the GBAS Landing System allows for CAT I (Category I) precision approaches, which provide a lateral and vertical navigation performance equivalent to that of Instrument Landing System (ILS) Category I approaches. It can also support CAT II (Category II) and CAT III (Category III) approaches with the necessary equipment and operational procedures.

2. Increased Flexibility

The GBAS Landing System offers increased flexibility compared to traditional ground-based navigation aids like ILS. Unlike ILS, which requires extensive ground installations and infrastructure, the GBAS Landing System can be implemented at airports with minimal ground infrastructure requirements. This makes it a cost-effective solution for airports that do not have the necessary resources or space to install traditional ILS systems.

Furthermore, the GBAS Landing System supports multiple approach procedures, including curved approaches and segmented approaches. This flexibility allows for more efficient use of airspace and enables airports to optimize their approach and landing procedures based on their specific operational needs.

3. Increased Safety

The GBAS Landing System enhances the safety of aircraft operations through its integrity monitoring capabilities. The system continuously checks the quality of the navigation signals and provides warnings to the flight crew in case of any anomalies or potential hazards. This ensures that the flight crew is aware of any potential issues and can make informed decisions to maintain the safety of the flight.

Additionally, the GBAS Landing System reduces the dependency on ground-based infrastructure for navigation, which can be susceptible to damage or failures. By relying on satellite signals and ground-based corrections, the system offers redundancy and increased resilience, ensuring continued navigation guidance even in the event of ground-based infrastructure disruptions.

For More: What is HUD in Aviation? (Head-Up Display)