Pilot/Controller Glossary 

10/5/23 

IFWP

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 Intermediate Fix Waypoint 

ILS

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(See INSTRUMENT LANDING SYSTEM.) 

ILS CATEGORIES

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 1. Category I. An ILS approach procedure which provides for approach to a height above 

touchdown of not less than 200 feet and with runway visual range of not less than 1,800 feet.

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 2. Special 

Authorization Category I. An ILS approach procedure which provides for approach to a height above touchdown 

of not less than 150 feet and with runway visual range of not less than 1,400 feet, HUD to DH. 3. Category II. 

An ILS approach procedure which provides for approach to a height above touchdown of not less than 100 feet 

and with runway visual range of not less than 1,200 feet (with autoland or HUD to touchdown and noted on 

authorization, RVR 1,000 feet).

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 4. Special Authorization Category II with Reduced Lighting. An ILS approach 

procedure which provides for approach to a height above touchdown of not less than 100 feet and with runway 

visual range of not less than 1,200 feet with autoland or HUD to touchdown and noted on authorization (no 

touchdown zone and centerline lighting are required).

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 5. Category III: 

a. 

IIIA.

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An ILS approach procedure which provides for approach without a decision height minimum and 

with runway visual range of not less than 700 feet. 

b. 

IIIB.

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An ILS approach procedure which provides for approach without a decision height minimum and 

with runway visual range of not less than 150 feet. 

c. 

IIIC.

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An ILS approach procedure which provides for approach without a decision height minimum and 

without runway visual range minimum. 
IM

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(See INNER MARKER.

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IMC

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(See INSTRUMENT METEOROLOGICAL CONDITIONS.) 

IMMEDIATELY

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Used by ATC or pilots when such action compliance is required to avoid an imminent 

situation. 
INCERFA (Uncertainty Phase) [ICAO]

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 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)

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(See SPEED ADJUSTMENT.) 

INERTIAL NAVIGATION SYSTEM (INS)

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 An RNAV system which is a form of self-contained navigation. 

(See Area Navigation/RNAV.) 

INFLIGHT REFUELING

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(See AERIAL REFUELING.) 

INFLIGHT SERVICES [FSS]– Services provided to or affecting aircraft inflight or otherwise operating on the 

airport surface. This includes services to airborne aircraft, such as the delivery of ATC clearances, advisories or 

requests, issuance of military flight advisory messages, NOTAM delivery, search and rescue communications 

searches, flight plan handling, transcribed or live broadcasts, weather observations, PIREPs, and pilot briefings. 
INFLIGHT WEATHER ADVISORY

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(See WEATHER ADVISORY.) 

INFORMATION REQUEST (INREQ)

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 A request originated by an FSS for information concerning an overdue 

VFR aircraft. 
INITIAL APPROACH FIX (IAF)

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 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.) 

PCG I

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