Aeronautical database as a critical system element

Aircraft for over four decades have been using radionavigation aids to safely navigate in controlled airspace. Navigation was relative to the navigation aid´s broadcast signal consisting of distance to/from the navaid (navigation aid) and bearing from the radionavigation aid to the aircraft, known as a radial. The navigation aid is aligned to local magnetic North. Magnetic North drifts with time; the navigation aid is permitted to differ from 3-5 degrees from current magnetic North without realignment. The difference between magnetic north at the time of alignment and True North is known as magnetic declination or slaved magnetic variation. Navigation aids that broadcast erroneous signals are detected within 10 seconds by the ground monitor, which turns the broadcast signal off. The paths over the ground of the broadcast signals define the airways. Because the actual ground tracks of the signals define the airways, the impact of any errors in the latitude and longitude or magnetic declination of the navigation aid are negated. Area Navigation is computer based and uses a digital database to go via Great Circle from one latitude/longitude point to another. When one of the points is a TACAN station the radial and magnetic declination of the navigation aid are used to determine the path over the Earth required to be on the desired airway. Undetected errors in the data will provide misleading and hazardous information to the aircrews. This paper covers how systems engineering is being applied to the aeronautical digital database as part of the total systems solution. Specific areas addressed include changes proposed and adopted by the National Imagery and Mapping Agency in the production of the Digital Aeronautical Flight Information File