Boeing's GPS Landing System Certified

Aviation Week & Space Technology 09/20/04
author: Michael Mecham

1-Meter Touchdown

Boeing has received FAA and JAA certification of a satellite-based automatic landing system that has demonstrated a runway centerline accuracy of 1 meter. A single system works for all runways at a host airport, can be applied regionally and has proved itself in equatorial regions, where signal consistency is a concern.

The Global Landing System (GLS) demonstrator aircraft was a 737-900 equipped with a Rockwell Collins GLU-925 multimode receiver (MMR). The GLU-925 is the first to include functionality for a Local Area Augmentation System (LAAS) and GLS, in addition to the more common instrument landing system (ILS) and Global Navigation Satellite System modes. The LAAS was developed by Honeywell.

Boeing's interest in GLS is part of a broad-range Technology Demonstrator effort the company launched two years ago aimed at reducing airport noise, improving pilots' awareness of terrain and increasing operational safety. The safety effort includes enhanced vision tools for darkness and inclement weather, a surface guidance system for taxiing aircraft and head-up displays. In fact, a GLS acting as a sensor instrument for an HUD in an A-3 mode was demonstrated successfully during the FAA and JAA certification trials both in landings and in low-altitude go-arounds.

THE CERTIFICATION is for Category 1 visual flight rules landings. Tom Imrich, Boeing's chief pilot for research, says airlines will want to build an experience base before proceeding to Cat. 2 and 3 reduced weather minimums operations.

Rockwell Collins has been able to enhance its standard 737NG MMR systems for more than a year to support auto-landings. However, certification was delayed until Collins had a production model available. The company will begin offering the GLU-925 as an update for its MMRs this autumn. The GLU-925 with an auto-land functionality for its Flight Management System will be offerable for Airbus platforms in late 2005, according to Rockwell Collins.

LAAS is regarded as a cost-effective advance over an ILS because a single system can provide landing control for multiple runways at a single airport, as well as runways at nearby airports. Its functionality includes an ability to provide multiple final approach paths, glideslope angles and missed approach paths for a given runway. In each case, the approach is given a unique identifier for a final approach segment that is transmitted to the aircraft with the same VHF Data Broadcast data link used for the satellite system.

In contrast, an ILS requires a separate system for each runway that is assigned its own frequency.
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The FAA/JAA certification was achieved at five airports in Washington. Two hubs were selected, Seattle/Tacoma International Airport and Moses Lake in central Washington, where Boeing conducts much of its flight testing. In the Seattle area, the reach of the LAAS was demonstrated with auto-landings at Boeing Field north of SeaTac and Paine Field at its wide-body assembly facilities at Everett. Besides demonstrating the reach of the LAAS, Imrich notes that Boeing Field is 400-ft. lower than SeaTac.

THE LAAS SIGNAL strength was also demonstrated with auto-landings at the Lake Ephrata airport near Moses Lake.

Flight tests in Brazil provided a more challenging test because the Boeing/ Collins/Honeywell system had to overcome concerns that ionospheric interference in such an equatorial region would affect signal propagation for estimates of the system's differential correction. The tests included auto-landings at Galeao International Airport in Rio de Janeiro and the Santodumont airport at 1,400 ft. at the base of Sugarloaf Mountain 7-8 mi. away.

The proximity of Santodumont's 4,300-ft. runway to the mountain requires a 180-deg. banking maneuver. Despite that, the GLS' LAAS facility was able to compensate well enough to provide auto-land corrections that put the 737 within 1 meter of the centerline.

This stuff is amazing. The accuracy they achieve with this system is incredible. The system give a much more accurate indication of aircraft position than the old ILS system, plus the total system costs will be reduced. Now we just need to certify the other aircraft and get some experience before we can move on to CAT III. The guys in Seattle, and Rockwell Collins are doing a great job with this technology!