Pilot/Controller Glossary

ALTERNATE AERODROME [ICAO]- An aerodrome to which an aircraft may proceed when it
becomes either impossible or inadvisable to proceed
to or to land at the aerodrome of intended landing.

accomplished. ALTRVs are approved by the
appropriate FAA facility.

Note: The aerodrome from which a flight departs
may also be an en-route or a destination alternate
aerodrome for the flight.

ALTITUDE RESTRICTION- An altitude or altitudes, stated in the order flown, which are to be
maintained until reaching a specific point or time.
Altitude restrictions may be issued by ATC due to
traffic, terrain, or other airspace considerations.

ALTERNATE AIRPORT- An airport at which an
aircraft may land if a landing at the intended airport
becomes inadvisable.
(See ICAO term ALTERNATE AERODROME.)

ALTIMETER SETTING- The barometric pressure
reading used to adjust a pressure altimeter for
variations in existing atmospheric pressure or to the
standard altimeter setting (29.92).
(Refer to 14 CFR Part 91.)
(Refer to AIM.)

ALTITUDE- The height of a level, point, or object
measured in feet Above Ground Level (AGL) or from
Mean Sea Level (MSL).
(See FLIGHT LEVEL.)

(See AIR TRAFFIC CONTROL SYSTEM
COMMAND CENTER.)

ALTITUDE RESTRICTIONS ARE CANCELED-
Adherence to previously imposed altitude restrictions is no longer required during a climb or descent.
ALTRV-
(See ALTITUDE RESERVATION.)

AMVER-
(See AUTOMATED MUTUAL-ASSISTANCE
VESSEL RESCUE SYSTEM.)

APB-
(See AUTOMATED PROBLEM DETECTION
BOUNDARY.)

a. MSL Altitude- Altitude expressed in feet
measured from mean sea level.

APD-

b. AGL Altitude- Altitude expressed in feet
measured above ground level.

APDIA-

c. Indicated Altitude- The altitude as shown by an
altimeter. On a pressure or barometric altimeter it is
altitude as shown uncorrected for instrument error
and uncompensated for variation from standard
atmospheric conditions.
(See ICAO term ALTITUDE.)

ALTITUDE [ICAO]- The vertical distance of a level,
a point or an object considered as a point, measured
from mean sea level (MSL).
ALTITUDE READOUT- An aircraft"s altitude,
transmitted via the Mode C transponder feature, that
is visually displayed in 100-foot increments on a
radar scope having readout capability.
(See ALPHANUMERIC DISPLAY.)
(See AUTOMATED RADAR TERMINAL
SYSTEMS.)
(Refer to AIM.)

ALTITUDE RESERVATION (ALTRV)- Airspace
utilization under prescribed conditions normally
employed for the mass movement of aircraft or other
special user requirements which cannot otherwise be

(See AUTOMATED PROBLEM DETECTION.)
(See AUTOMATED PROBLEM DETECTION
INHIBITED AREA.)

APPROACH CLEARANCE- Authorization by
ATC for a pilot to conduct an instrument approach.
The type of instrument approach for which a
clearance and other pertinent information is provided
in the approach clearance when required.
(See CLEARED APPROACH.)
(See INSTRUMENT APPROACH
PROCEDURE.)
(Refer to AIM.)
(Refer to 14 CFR Part 91.)

APPROACH CONTROL FACILITY- A terminal
ATC facility that provides approach control service in
a terminal area.
(See APPROACH CONTROL SERVICE.)
(See RADAR APPROACH CONTROL
FACILITY.)

APPROACH CONTROL SERVICE- Air traffic
control service provided by an approach control
facility for arriving and departing VFR/IFR aircraft
and, on occasion, en route aircraft. At some airports