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12/2/21 

Pilot/Controller Glossary 

minimum and with runway visual range of not less 
than 150 feet. 

c. 

IIIC.

An ILS approach procedure which 

provides for approach without a decision height 
minimum and without runway visual range 
minimum. 

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 5 
NM separation. 3 NM separation, 1 

½

 NM 

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 self­contained 
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 

PCG I