Pilot/Controller Glossary

conduct these approaches. ATC utilizes an enhanced
display with alerting and, with certain runway
spacing, a high update rate PRM surveillance sensor.
Use of a secondary monitor frequency, pilot PRM
training, and publication of an Attention All Users
Page are also required for all PRM approaches.
(Refer to AIM)

IM-
(See INNER MARKER.)

IMC-
(See INSTRUMENT METEOROLOGICAL
CONDITIONS.)

IMMEDIATELY- Used by ATC or pilots when such
action compliance is required to avoid an imminent
situation.
INCERFA (Uncertainty Phase) [ICAO]- A situation
wherein uncertainty exists as to the safety of an
aircraft and its occupants.
INCREASED SEPARATION REQUIRED (ISR)"
Indicates the confidence level of the track requires
5NM separation. 3NM separation, 1 1/2NM
separation, and target resolution cannot be used.
INCREASE SPEED TO (SPEED)-
(See SPEED ADJUSTMENT.)

INERTIAL NAVIGATION SYSTEM (INS)- An
RNAV system which is a form of self-contained
navigation.
(See Area Navigation/RNAV.)

INFLIGHT REFUELING-
(See AERIAL REFUELING.)

INFLIGHT WEATHER ADVISORY-
(See WEATHER ADVISORY.)

INFORMATION REQUEST (INREQ)- A request
originated by an FSS for information concerning an
overdue VFR aircraft.
INITIAL APPROACH FIX (IAF)- The fixes
depicted on instrument approach procedure charts
that identify the beginning of the initial approach
segment(s).
(See FIX.)
(See SEGMENTS OF AN INSTRUMENT
APPROACH PROCEDURE.)

INITIAL APPROACH SEGMENT-
(See SEGMENTS OF AN INSTRUMENT
APPROACH PROCEDURE.)

INITIAL APPROACH SEGMENT [ICAO]- That
segment of an instrument approach procedure
between the initial approach fix and the intermediate
approach fix or, where applicable, the final approach
fix or point.
INLAND NAVIGATION FACILITY- A navigation
aid on a North American Route at which the common
route and/or the noncommon route begins or ends.
INNER MARKER- A marker beacon used with an
ILS (CAT II) precision approach located between the
middle marker and the end of the ILS runway,
transmitting a radiation pattern keyed at six dots per
second and indicating to the pilot, both aurally and
visually, that he/she is at the designated decision
height (DH), normally 100 feet above the touchdown
zone elevation, on the ILS CAT II approach. It also
marks progress during a CAT III approach.
(See INSTRUMENT LANDING SYSTEM.)
(Refer to AIM.)

INNER MARKER BEACON-
(See INNER MARKER.)

INREQ-
(See INFORMATION REQUEST.)

INS-
(See INERTIAL NAVIGATION SYSTEM.)

INSTRUMENT APPROACH-
(See INSTRUMENT APPROACH
PROCEDURE.)

INSTRUMENT APPROACH OPERATIONS
[ICAO]- An approach and landing using instruments
for navigation guidance based on an instrument
approach procedure. There are two methods for
executing instrument approach operations:
a. A two-dimensional (2D) instrument approach
operation, using lateral navigation guidance only;
and
b. A three-dimensional (3D) instrument approach
operation, using both lateral and vertical navigation
guidance.
Note: Lateral and vertical navigation guidance
refers to the guidance provided either by:
a) a ground-based radio navigation aid; or
b) computer-generated navigation data from
ground-based, space-based, self-contained
navigation aids or a combination of these.
(See ICAO term INSTRUMENT APPROACH
PROCEDURE.)

INSTRUMENT APPROACH PROCEDURE- A
series of predetermined maneuvers for the orderly