Pilot/Controller Glossary

D-ATIS-
(See DIGITAL-AUTOMATIC TERMINAL
INFORMATION SERVICE.)

D-ATIS [ICAO]-
(See ICAO Term DATA LINK AUTOMATIC
TERMINAL INFORMATION SERVICE.)

DA [ICAO]-
(See ICAO Term DECISION
ALTITUDE/DECISION HEIGHT.)

DAIR-
(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.

DAS-
(See DELAY ASSIGNMENT.)

DATA BLOCK-
(See ALPHANUMERIC DISPLAY.)

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.)

DATA LINK AUTOMATIC TERMINAL INFORMATION SERVICE (D-ATIS) [ICAO]- The
provision of ATIS via data link.

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.

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.

DEFENSE VISUAL FLIGHT RULES- Rules
applicable to flights within an ADIZ conducted under
the visual flight rules in 14 CFR Part 91.

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 minimre 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 minim DH.

(See AIR DEFENSE IDENTIFICATION ZONE.)
(Refer to 14 CFR Part 91.)
(Refer to 14 CFR Part 99.)

DELAY ASSIGNMENT (DAS)- Delays are distributed 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