ABSTRACT
The task of navigation (“Nav”) interacts with multiple avionics functions. To clarify the focus here, this chapter will not discuss tight formations, guidance, steering, minimization of fuel/noise/pollution, or managing time of arrival. The accent instead is on determining position and velocity (plus, where applicable, other variables such as acceleration, verticality, heading) with maximum accuracy reachable from whatever combination of sensor outputs are available at any time. Position can be expressed as a vector displacement from a designated point or in terms of latitude/longitude/altitude above mean sea level, above the geoid-or both. Velocity can be expressed in a locally level coordinate frame with various choices for an azimuth reference (e.g., geodetic North, Universal Transverse Mercator [UTM] grid North, runway centerline, wander azimuth with or without Earth sidereal rate torquing). In principle any set of axes could be used — such as an Earth Centered Earth Fixed (ECEF) frame for defining position by a Cartesian vector; or velocity in Cartesian coordinates or in terms of groundspeed, flight path angle, and ground track angle — in either case it is advisable to use accepted conventions.
