Pilot/Controller Glossary

4/3/14

PCG A−10

ALERFA (Alert Phase) [ICAO]− A situation wherein

apprehension exists as to the safety of an aircraft and

its occupants.
ALERT− A notification to a position that there

is an aircraft-to-aircraft or aircraft-to-airspace

conflict, as detected by Automated Problem

Detection (APD).
ALERT AREA−

(See SPECIAL USE AIRSPACE.)

ALERT NOTICE− A request originated by a flight

service station (FSS) or an air route traffic control

center (ARTCC) for an extensive communication

search for overdue, unreported, or missing aircraft.
ALERTING SERVICE− A service provided to notify

appropriate organizations regarding aircraft in need

of search and rescue aid and assist such organizations

as required.
ALNOT−

(See ALERT NOTICE.)

ALONG−TRACK DISTANCE (ATD)− The distance

measured from a point-in-space by systems using

area navigation reference capabilities that are not

subject to slant range errors.
ALPHANUMERIC DISPLAY− Letters and numer-

als used to show identification, altitude, beacon code,

and other information concerning a target on a radar

display.

(See AUTOMATED RADAR TERMINAL

SYSTEMS.)

ALTERNATE AERODROME [ICAO]− An aero-

drome 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.

Note: The aerodrome from which a flight departs

may also be an en-route or a destination alternate
aerodrome for the flight.

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.)

a.

MSL Altitude− Altitude expressed in feet

measured from mean sea level.

b.

AGL Altitude− Altitude expressed in feet

measured above ground level.

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− Airspace utilization

under prescribed conditions normally employed for

the mass movement of aircraft or other special user

requirements which cannot otherwise be

accomplished. ALTRVs are approved by the

appropriate FAA facility.

(See AIR TRAFFIC CONTROL SYSTEM

COMMAND CENTER.)

ALTITUDE RESTRICTION− An altitude or alti-

tudes, 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.
ALTITUDE RESTRICTIONS ARE CANCELED

−

Adherence to previously imposed altitude restric-

tions 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.)