Aircraft Systems

8Global Navigation Satellite System (GNSS)

Satellite navigation has become the mainstay of all global navigation systems and is an indispensable tool in modern aviation. The convenience of use and relatively low cost of the user equipment has led to the installation of GNSS navigation receivers in virtually all aircraft from gliders to commercial jet transport. Increasingly, procedures are being implemented for aircraft to approach and land using GNSS as well as navigate enroute so that in the near future it is likely that most flights can be conducted under IMC conditions using only satellite navigation. The important requirement for redundancy, however, means that the onboard equipment and infrastructure for all other navigation systems will be maintained including inertial navigation and the radio beacons described in Chapter 7. In practice, in a commercial airliner, the navigational information from all sources is combined using Kalman filtering to produce an instantaneous three‐dimensional position fix as described in Chapter 9. In this chapter the infrastructure, signals, and cockpit equipment required for navigation by satellite will be described.

8.1 Basic Principle of Satellite Navigation

A GNSS system employs a constellation of satellites orbiting the Earth so that a vehicle always has line of sight with several of them. Each satellite has an atomic clock on board that is synchronized to the clocks on the other satellites and to atomic clocks on the ground that ...