DIGITAL‐AUTOMATIC TERMINAL INFORMA-TION SERVICE (D‐ATIS)- The service provides text messages to aircraft, airlines, and other users outside the standard reception range of conventional ATIS via landline and data link communications to the cockpit. Also, the service provides a computer-synthesized voice message that can be transmitted to all aircraft within range of existing transmitters. The Terminal Data Link System (TDLS) D‐ATIS application uses weather inputs from local automated weather sources or manually entered meteorological data together with preprogrammed menus to provide standard information to users. Airports with D‐ATIS capability are listed in the Airport/Facility Directory.
DIGITAL TARGET- A computer-generated symbol representing an aircraft's position, based on a primary return or radar beacon reply, shown on a digital display.
DIGITAL TERMINAL AUTOMATION SYSTEM (DTAS)- A system where digital radar and beacon data is presented on digital displays and the operational program monitors the system perfor-mance on a real-time basis.
DIGITIZED TARGET- A computer-generated indication shown on an analog radar display resulting from a primary radar return or a radar beacon reply.
DIRECT-Straight line flight between two naviga-tional aids, fixes, points, or any combination thereof. When used by pilots in describing off‐airway routes, points defining direct route segments become compulsory reporting points unless the aircraft is under radar contact.
DIRECT ALTITUDE AND IDENTITY READ‐OUT-The DAIR System is a modification to the AN/TPX‐42 Interrogator System. The Navy has two adaptations of the DAIR System‐Carrier Air Traffic Control Direct Altitude and Identification Readout System for Aircraft Carriers and Radar Air Traffic Control Facility Direct Altitude and Identity Readout System for land‐based terminal operations. The DAIR detects, tracks, and predicts secondary radar aircraft targets. Targets are displayed by means of computer‐generated symbols and alphanumeric characters depicting flight identification, altitude, ground speed, and flight plan data. The DAIR System is capable of interfacing with ARTCCs.

DIRECTION FINDER- A radio receiver equipped with a directional sensing antenna used to take bearings on a radio transmitter. Specialized radio direction finders are used in aircraft as air navigation aids. Others are ground‐based, primarily to obtain a “fix” on a pilot requesting orientation assistance or to locate downed aircraft. A location “fix” is established by the intersection of two or more bearing lines plotted on a navigational chart using either two separately located Direction Finders to obtain a fix on an aircraft or by a pilot plotting the bearing indications of his/her DF on two separately located ground‐based transmitters, both of which can be identified on his/her chart. UDFs receive signals in the ultra high frequency radio broadcast band; VDFs in the very high frequency band; and UVDFs in both bands. ATC provides DF service at those air traffic control towers and flight service stations listed in the Airport/Facility Directory and the DOD FLIP IFR En Route Supplement.