GBAS Systems

Fundamentals
Title	GBAS Systems
Author(s)	GMV
Level	Basic
Year of Publication	2011

A Ground-Based Augmentation System (GBAS) is a civil-aviation safety-critical system that supports local augmentation – at airport level – of the primary GNSS constellation(s) by providing enhanced levels of service that support all phases of approach, landing, departure and surface operations.

The pioneering and reference GBAS system is the United States one:

-The Local Area Augmentation System (LAAS)

Local Area Augmentation System (LAAS)

The Local Area Augmentation System (LAAS) is designed to correct some of the errors inherent to GPS. One problem is the lack of a real-time, rapid-response monitoring system. Category I equipment will normally alert the user of the problem within ten seconds of detecting a problem. GPS has no such rapid-warning system. For example, if a develops a clock problem, there is no way to rapidly warn the user not to use that satellite. WAAS, LAAS and other differential solutions fix this problem and provide GPS system integrity. Another problem is positional accuracy. Sources of error such as satellite or ionospheric delays can introduce several meters of error in an aircraft's position. These errors must be corrected in real time for a precision approach where there is little or no visibility.

Honeywell has developed a Non-Federal CAT-1 LAAS which received System Design Approval (SDA) from the Federal Aviation Administration (FAA) in September 2009 Current proposed installations include: airports in Newark, NJ; Memphis, TN; Atlantic City, NJ; and Olathe, KS.

One of the primary benefits of LAAS is that a single installation at a major airport can be used for multiple precision approaches within the local area. For example, if Chicago O'Hare has 12 runway ends each with a separate ILS, all 12 ILS facilities can be replaced with a single LAAS system. This represents a significant cost savings in maintenance and upkeep of the existing ILS equipment. Another benefit is the potential for approaches that are not straight- in. Aircraft equipped with LAAS technology can utilize curved or complex approaches such that they could be flown on to avoid obstacles or to decrease noise levels in areas surrounding an airport.

The FAA also contends that only a single set of navigational equipment will be needed on an aircraft for both LAAS and WAAS capability. This lowers initial cost and maintenance per aircraft

Other GBAS implementations

The Honeywell’s SmartPath is the most commonly used GBAS solution to increase airport capacity, decrease air traffic noise, and reduce weather-related delays.

Future

The FAA’s National Airspace System (NAS) Enterprise Architecture is the blueprint for transforming the current NAS to the Next Generation Air Transportation System (NextGen). The NAS Service Roadmaps lay out the strategic activities for service delivery to improve NAS operations and move towards the NextGen vision. They show the evolution of major FAA investments/programs in today's NAS services to meet the future demand. The GBAS Precision Approaches is one of the investment programs that provide solution to “Increase Flexibility n the Terminal Environment” in the NextGen Implementation Plan.

The FAA plans to replace legacy navigation systems with satellite based navigation technology. The FAA has determined that GBAS is the only cost effective alternative to the existing Instrument Landing Systems (ILS) by providing terminal, non-precision, and CAT I/II/III precision approach capabilities in the NAS. Some of these existing ILS systems will be phased out over time as GBAS are installed. A number of ILS facilities are expected to remain operational, to continue to provide precision approach service as a backup in the event of unavailability of GBAS services. This plan has been also envisaged by Eurocontrol’s Single European Sky ATM Research Programme as a critical enabler for improving air traffic capacity.