Introduction

Ground-based augmentation system (GBAS) is a navigation system that supports aircraft precision approaches even in poor weather conditions, but conditions in the earth’s upper atmosphere (ionosphere) can interfere with the system’s signalling and overall performance. So, while a GBAS landing system (GLS) helps to maintain safety and capacity performance using just one ground station for multiple runway operations, the performance of the system and category of approach depends upon integrity levels. 

This SESAR Solution relies on the existing GBAS approach service type (GAST) equipment and satellite-based augmentation system (SBAS) messages to better monitor signalling and GBAS service integrity.

About the Solution 

The GBAS approach service type (GAST) describes the level of service provided by a specific GBAS facility. Standard GAST-C does not monitor whether conditions in the upper earth atmosphere are influencing the performance of the system. If the system cannot assure integrity requirements, the service ‘defaults’ to a lower level, and only CAT I operations are supported. 

To address this, the enhanced GAST-C ground station makes use of SBAS messages to monitor unusual conditions in the upper earth atmosphere. Then, when the navigation position is properly bounded, CAT II operations can be performed. 

Key features include:

• Supports CAT-II operations - a precision instrument approach with a decision height below 200ft but not less than 100ft and with a runway visual range (RVR) of 300m (1000ft).
• Applies aircraft separation and latest point of landing clearance.
• Availability is broadcast in the automatic terminal information service (ATIS), as is the service level.
• If the ATIS has not been updated after a change in GAST-C service level, controllers will inform pilots directly over the radio.
• For GAST-C, air traffic control is the sole source of information for pilots regarding service level degradation, there is no onboard alert.

The Solution delivers increased runway capacity in poor weather conditions since it is unaffected by interference from previous landing aircraft or other obstacles. There is also sustained accuracy in aircraft guidance on final approach.

Benefits 

   • GBAS GAST-C / CAT I equipment is sufficient
   • One GBAS ground station can be used for multiple runway operations
   • The instrument landing system (ILS) critical and sensitive areas are no longer restricted
   • Reduced interference from previous landing aircraft or other obstacles
   • Sustained accuracy in aircraft guidance on final approach
   • Increased runway capacity in poor weather conditions 
 

Datapack

CN Solution #119 GLS CAT II operation using GBAS GAST-C 
SESAR 2020 AAL2 DEMO Report  
Appendix A to SESAR 2020 AAL2 DEMO Report 
Appendix B to SESAR 2020 AAL2 DEMO Report 
Appendix C and D to SESAR 2020 AAL2 DEMO Report 
Appendix E to SESAR 2020 AAL2 DEMO Report 
Appendix F G H and I to SESAR 2020 AAL2 DEMO Report 
Appendix J K and L to SESAR 2020 AAL2 DEMO Report