Professor Umran Inan

Winter 2001-2002

Date: Wednesday, February 20, 2002
Time: 4:15-5:30 PM; Refreshments at 4:00 PM
Location: Bldg. 320, Rm #221

Landing Airplanes Using Satellite Signals

Professor Per Enge
Aeronautics and Astronautics, Stanford University


These days, the aviation community is steadily increasing its reliance on the Global Navigation Satellite Systems (GNSS) as the primary means of navigation for all phases of flight. The most advanced of the GNSS is the Global Positioning System (GPS). GPS is already used as a supplemental aid for flight over oceanic routes, enroute through our domestic airspace, and in crowded metropolitan airspaces. GPS is also used for a growing number of airport approach operations. During non-precision approach, it is used solely for horizontal positioning. Together with inertial and air data measurements, GPS supports precision approach at Juneau as well as several other Alaskan cities. In differential mode, it has been installed to provide vertical guidance at Newark, Minneapolis, and Chicago O¹Hare airports.

To facilitate this important trend, the international aviation community is deploying two differential GPS systems called the Wide Area Augmentation System (WAAS) and the Local Area Augmentation System (LAAS). Both systems use high-quality receivers at known locations to develop corrections to the signals from the satellites and to bound the error of the corrected signal. The corrections improve the nominal accuracy (95%) of stand-alone service, and the error bounds guarantee the integrity (10-7) of the approach. LAAS provides the very high accuracy and integrity required to support precision approach operations at our busiest airports. WAAS supports operations over continental areas including precision approach operations at small and medium airports.

At Stanford, we have supported the development of both WAAS and LAAS with research and tests directed at the fundamental error sources, algorithms, safety and operational benefits. In collaboration with the FAA Technical Center (FAATC), we have developed complete prototypes of both systems.

This talk will describe some exciting current applications of GPS to aviation. It will also provide a brief report on the development of WAAS and LAAS in the United States. Next, it will discuss the current challenges that face GPS use for aviation. These include safety analyses and radio frequency interference. Finally, it will describe the long and short term strategies to overcome these challenges.