A Ground-Based Augmentation System (GBAS) provides localized augmentation of GNSS to support precision approach and landing operations. Its architecture combines ground infrastructure, airborne equipment and a VHF data link to deliver high-integrity corrections and guidance for GNSS Landing System (GLS) approaches.
This page summarizes the main GBAS architecture elements, how they interact, the data flows involved, and key design and implementation considerations.
At a high level, a GBAS installation:
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Receives GNSS signals via multiple ground reference receivers
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Generates differential corrections, integrity parameters and approach-specific data in a Ground Facility
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Broadcasts this information via a VHF Data Broadcast (VDB) to nearby aircraft
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Enables airborne receivers to compute a precision approach solution for GLS procedures aligned with specific runways
The architecture is designed so that integrity monitoring, fault detection and exclusion (FDE) are primarily handled on the ground, while airborne equipment focuses on applying broadcast corrections and generating guidance within defined protection levels.
1. Reference Receiver Network
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Multiple GNSS antennas and receivers strategically located on the airfield
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Provide measurements for all satellites in view (and all supported constellations/frequencies)
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Enable detection of local anomalies such as multipath, interference or ionospheric gradients
2. Ground Facility / Processing Unit
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Central processing system that:
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Computes differential corrections and integrity parameters
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Performs fault detection and exclusion on reference receivers and satellites
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Manages configuration, monitoring, and logging for certification and maintenance
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3. VHF Data Broadcast (VDB) Subsystem
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One or more VHF transmitters and antennas
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Broadcasts GBAS messages containing:
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Pseudorange corrections
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Integrity and protection information
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GLS approach data (path, geometry, reference path identifiers)
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Designed for high availability and low latency within the coverage area around the airport
4. Monitoring and Control Interfaces
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Local or remote monitoring workstations for:
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System health and alarm status
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Configuration and maintenance activities
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Data recording for performance analysis and regulatory compliance
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1. GBAS-Capable GNSS Receiver
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Receives GNSS signals and the GBAS VDB broadcast
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Applies differential corrections and integrity data
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Computes position, protection levels and deviation signals suitable for precision approach guidance
2. Flight Management and Guidance Integration
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Interfaces to Flight Management System (FMS), autopilot, and flight director
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Provides localizer-like and glideslope-like guidance for GLS approaches
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For CAT II/III and autoland capability, integrates with certified autoland systems and redundancy paths
3. Flight Deck Indications
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Displays GLS approaches in a manner consistent with other precision approaches (e.g. ILS)
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Supports standardised naming conventions and annunciations so that pilots can select and fly GLS procedures with minimal additional workload
Because GBAS supports safety-critical operations, its architecture incorporates multiple layers of protection:
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Multiple Reference Receivers
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Used to cross-check measurements and detect failures or anomalies at a single antenna/receiver site.
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Diverse Monitoring Algorithms
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Parallel integrity checks to guard against different threat types (e.g. satellite faults, ionospheric gradients, local interference).
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Redundant Ground Subsystems
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In higher levels of service, multiple processors, power supplies, VDB transmitters and communication paths can be included.
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Designed so that a single failure does not immediately interrupt service or compromise integrity.
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Fail-Safe Behaviour
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In case of detected anomalies or failures, the system transitions to a safe state, which may include reducing the available service or shutting down broadcasts to prevent misleading information.
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