Pilot/Controller Glossary  8/15/19  D  D-ATIS- D-ATIS [ICAO]- DA [ICAO]- DAIR- (See DIGITAL-AUTOMATIC TERMINAL  INFORMATION SERVICE.)  (See ICAO Term DATA LINK AUTOMATIC  TERMINAL INFORMATION SERVICE.)  (See ICAO Term DECISION  ALTITUDE/DECISION HEIGHT.)  (See DIRECT ALTITUDE AND IDENTITY  READOUT.)  DANGER AREA [ICAO]- An airspace of defined  dimensions within which activities dangerous to the  flight of aircraft may exist at specified times.  Note: The term “Danger Area” is not used in  reference to areas within the United States or any  of its possessions or territories.  (See  DELAY ASSIGNMENT .)  (See ALPHANUMERIC DISPLAY.)  DAS- DATA BLOCK- DATA LINK AUTOMATIC TERMINAL INFOR- MATION SERVICE (D-ATIS) [ICAO]- The  provision of ATIS via data link.  DEAD RECKONING- Dead reckoning, as applied  to flying, is the navigation of an airplane solely by  means of computations based on airspeed, course,  heading, wind direction, and speed, groundspeed,  and elapsed time.  DECISION ALTITUDE/DECISION HEIGHT  [ICAO Annex 6]- A specified altitude or height (A/H)  in the precision approach at which a missed approach  must be initiated if the required visual reference to  continue the approach has not been established.  1. Decision altitude (DA) is referenced to mean sea  level and decision height (DH) is referenced to the  threshold elevation.  2. Category II and III minima are expressed as a DH  and not a DA. Minima is assessed by reference to a  radio altimeter and not a barometric altimeter, which  makes the minima a DH.  3. The required visual reference means that section of  the visual aids or of the approach area which should  have been in view for sufficient time for the pilot to  have made an assessment of the aircraft position and  rate of change of position, in relation to the desired  flight path.  DECISION ALTITUDE (DA)- A specified altitude  (mean sea level (MSL)) on an instrument approach  procedure (ILS, GLS, vertically guided RNAV) at  which the pilot must decide whether to continue the  approach or initiate an immediate missed approach if  the pilot does not see the required visual references.  DECISION HEIGHT (DH)- With respect to the  operation of aircraft, means the height at which a  decision must be made during an ILS or PAR  instrument approach to either continue the approach  or to execute a missed approach.  (See ICAO term DECISION  ALTITUDE/DECISION HEIGHT.)  DECODER- The device used to decipher signals  received from ATCRBS transponders to effect their  display as select codes.  (See CODES.)  (See RADAR.)  DEFENSE AREA– Any airspace of the contiguous  United States that is not an ADIZ in which the control  of aircraft is required for reasons of national security.  DEFENSE VISUAL FLIGHT RULES- Rules  applicable to flights within an ADIZ conducted under  the visual flight rules in 14 CFR Part 91.  (See AIR DEFENSE IDENTIFICATION ZONE.)  (Refer to 14 CFR Part 91.)  (Refer to 14 CFR Part 99.)  DELAY ASSIGNMENT (DAS)- Delays are distrib- uted to aircraft based on the traffic management  program parameters. The delay assignment is  calculated in 15-minute increments and appears as a  table in Traffic Flow Management System (TFMS) .  DELAY INDEFINITE (REASON IF KNOWN)  EXPECT FURTHER CLEARANCE (TIME) - Used by ATC to inform a pilot when an accurate  estimate of the delay time and the reason for the delay  cannot immediately be determined; e.g., a disabled  PCG D-1 