GBAS not dead, despite FAA reversal
Boeing’s delivery in May of a 737-800 airliner certified for the global navigation satellite landing system (GLS) marked the culmination of a 10-year development effort. It also served as a reminder that the ground-based augmentation system (GBAS) still has a future, despite a U.S. Federal Aviation Administration (FAA) decision last year to cancel production contracts for ground stations and reclassify the activity as a research and development project.
Switzerland’s Skyguide air traffic control service had considered a GBAS installation at Zurich after authorities downgraded the Category III instrument landing system (ILS) there because of interference caused by a crane used for construction work. However, the Swiss program follows a “delta certification” process under which the FAA would accept certification of the ground equipment and independently certify items such as maintenance and ATC interfaces. The FAA’s move away from implementation led Skyguide to opt for two ILS installations with end-fire antennas for the Zurich Runways 34 and 28.
The most ambitious program is in Germany, where air navigation services provider Deutsche Flugsicherung (DFS) started implementing satellite-based approaches in the mid-1990s. By mid-1999 it had published stand-alone GPS approach procedures for all the country’s airports. In mid-March the company received budget approval to embark on the development of GBAS-based Category I precision approaches, and ultimately Category II and III procedures. The project is due for completion by 2008.
The DFS has been using a Honeywell ground station for trials at Frankfurt for some time and hopes it can update that system to comply with ICAO Annex 10 standards and recommended practices. If no upgrade is available, the DFS would likely seek a new ground station from Honeywell or Thales. It has selected Bremen airport for development of the approach procedures. An international airport with a Category III ILS, it functions under the aegis of the DFS and hosts operations by Lufthansa. Spain’s AENA uses another prototype Honeywell GBAS ground station for trials at Malaga.
Both Boeing and Airbus want to see GBAS technology put into use in time for service entry of the 787 and A380. The GLS-capable Boeing 737-800 carries a Rockwell Collins GLU-925 multi-mode receiver. Certified last August for Category I approaches and capable of supporting future Category III operations, a version of the GLU-925 that supports Airbus’ non-precision FMS landing system (FLS) is also available for all that company’s aircraft. The FLS generates a pseudo guidance beam to provide ILS look-alike guidance.
The FAA, meanwhile, has continued making progress with some of the main technical challenges of LAAS. With Honeywell and Stanford University it has succeeded in modeling the worst-case ionospheric threat and proposed methods of monitoring ionospheric interferences. With those partners and Ohio State University it has established a method to monitor and counteract ground errors, a necessary step in providing adequate continuity and integrity.