GNSS Frequently Asked Questions – LAAS

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What is GBAS?

The Ground Based Augmentation System (GBAS) is a satellite navigation system being developed by the FAA. GBAS uses signals from the Global Positioning System (GPS) to develop an extremely accurate navigation signal that focuses its service on the airport area (approximately a 20-30 mile radius).

How is GBAS different than WAAS?

Like the Wide Area Augmentation System (WAAS), GBAS relies on GPS for basic navigation signals. However, with WAAS, GPS-corrected navigation signals come from space, broadcast from WAAS geostationary satellites. With GBAS, the GPS-corrected navigation signal is broadcast from a GBAS VHF data broadcast transmitter at or near the airport. Although GBAS and WAAS will operate independently, GBAS will complement WAAS by providing GNSS Landing System (GLS) landing service for Category II/III precision approach operations. GBAS will also provide GLS Category-I capability at locations where WAAS service may not be available. Other differences between WAAS and GBAS include the manner in which the availability of the systems are computed, the manner in which avionics receive information on approach procedures, and the vertical alert limits (VAL) associated with each system.

Is GBAS Still In Development?

Yes. GBAS was directed back to a research & development program in February 2004 to lower overall program risk and resolve integrity issues. The U.S. air carrier/cargo users want a seamless worldwide navigation capability and continue to support GBAS. The preferred instrument approach procedure types in the terminal area for air carriers are Performance Based Navigation or Required Navigation Performance (RNP) and GLS precision approach provided by GBAS. GBAS also supports the FAA strategic plans to transition to satellite navigation.

What are the next steps for GBAS?

The FAA is pursuing a Non-Federal Category I GBAS system. The FAA currently has a contract with Honeywell for the development of GBAS. Additionally, Honeywell has entered into an agreement with Airservices Australia (ASA) to complete the development, certification and joint commercialization of a Ground-Based Augmentation System (GBAS). [GBAS is the international term for GBAS.] ASA will develop a certifiable system to be installed at Sydney under a separate Honeywell contract.

This GBAS development will be a jointly-sponsored FAA and ASA effort. The FAA will sponsor new processor redesign, GPS reference receiver hardware development (DO-254, Level B), and operating system upgrades. ASA will sponsor everything else.

The goal is to get the Memphis system approved as an ICAO Non-Federal Standards and Recommended Practices (SARPs) compliant Category I system in late 2008, the same time the ASA system would be approved in Sydney.

Honeywell will apply for regulatory approval of the SLS-4000 GBAS ground facility at Memphis. The FAA will conduct test & evaluation activities at the FAA Technical Center. FedEx will submit an application for specials approval at Memphis.

The FAA will also complete facility and service approval plans to ensure the operational and user requirements are in place. FAA�s Aviation Systems Standards organization (AVN) is designing and flight inspecting 8 straight-in Category I Instrument Landing System (ILS) overlay approaches at Memphis. The FAA is also doing research on developing Terminal Area Path (TAP) procedures using existing RNP and RNAV criteria. A TAP is a curved path procedure that can begin at the fringes of the terminal area and end in a Category I GBAS approach, while maintaining the most stringent RNP equivalent values. The FAA will determine the feasibility of TAP as a potential implementation of RNP/RNAV and conduct flight testing at the FAA Technical Center and in Memphis to validate performance.

What can GBAS do for my Airport?

GBAS can provide Category I precision landing to all runway ends with one system while eliminating most ILS critical areas. The eventual goal for GBAS is Category II/III service.

What is the benefit of a GBAS Category I system vs. an ILS Category I system?

One GBAS system supports multiple runway ends. GBAS eliminates ILS critical areas. GBAS can support curved path approaches. GBAS provides guided missed approaches and departures.

What is the status of GBAS CAT II/III?

The FAA Technical Center, in conjunction with Boeing and other FAA entities, are developing the high level requirements for a Category II/III GBAS. In addition, the FAA is examining the possibility of using advanced navigation and landing technologies onboard newer digital aircraft to augment existing Category I GBAS technology to attain Category II/III functionality for these specific aircraft.

What is the status of GBAS avionics development?

Rockwell Collins recently received FAA certification approval for their multimode receiver (MMR). Boeing has incorporated this GBAS/GLS functionality on their 737-800 NG series aircraft. Qantas Airlines has purchased several of these GBAS capable Boeing aircraft in anticipation of a future GBAS ground station at Sydney. Continental Airlines has retrofitted nine of its 737-NG with GLS in anticipation of a GBAS System being installed in Guam and a German Air Carrier recently purchased a new GBAS equipped Boeing 737-NG to fly against a new GBAS system in Bremen, Germany. Airbus plans to offer GLS functionality on several of its airframe types to include the new Airbus A380.

How current does my airport�s last survey have to be to meet GBAS survey requirements?

The most important part about the survey is that the runway ends have been surveyed in accordance with FAA No. 405, �Standards for Aeronautic Surveys and Related Products�, which describes the accuracy of the runway coordinates. If a survey was done to support WAAS or other precision NAVAID installations, it should be OK.

Will we have to have a new airport survey just for GBAS?

A new airport survey won�t be needed to support GBAS if it is replacing an ILS, but where a new service or approach is being introduced, a new obstacle survey may be needed. The GBAS installer will need to survey the GBAS reference locations, but it should be possible to do that from existing benchmarks.