4/20/23 

Pilot/Controller Glossary 

I 

I SAY AGAIN

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The message will be repeated. 

IAF

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(See INITIAL APPROACH FIX.) 

IAP

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(See INSTRUMENT APPROACH PROCEDURE.) 

IAWP

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 Initial Approach Waypoint 

ICAO

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(See ICAO Term INTERNATIONAL CIVIL AVIATION ORGANIZATION.) 

ICAO 3LD

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(See ICAO Term ICAO Three

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Letter Designator) 

ICAO Three

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Letter Designator (3LD)

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 An ICAO 3LD is an exclusive designator that, when used together with 

a flight number, becomes the aircraft call sign and provides distinct aircraft identification to air traffic control 

(ATC). ICAO approves 3LDs to enhance the safety and security of the air traffic system. An ICAO 3LD may 

be assigned to a company, agency, or organization and is used instead of the aircraft registration number for ATC 

operational and security purposes. An ICAO 3LD is also used for aircraft identification in the flight plan and 

associated messages and can be used for domestic and international flights. A telephony associated with an 

ICAO 3LD is used for radio communication. 
ICING

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 The accumulation of airframe ice. 

Types of icing are: 

a. 

Rime Ice

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Rough, milky, opaque ice formed by the instantaneous freezing of small supercooled water 

droplets. 

b. 

Clear Ice

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 A glossy, clear, or translucent ice formed by the relatively slow freezing of large supercooled 

water droplets. 

c. 

Mixed

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 A mixture of clear ice and rime ice. 

Intensity of icing: 

a. 

Trace

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 Ice becomes noticeable. The rate of accumulation is slightly greater than the rate of sublimation. 

A representative accretion rate for reference purposes is less than 

¼

 inch (6 mm) per hour on the outer wing. The 

pilot should consider exiting the icing conditions before they become worse. 

b. 

Light

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 The rate of ice accumulation requires occasional cycling of manual deicing systems to minimize 

ice accretions on the airframe. A representative accretion rate for reference purposes is 

¼

 inch to 1 inch (0.6 to 

2.5 cm) per hour on the unprotected part of the outer wing. The pilot should consider exiting the icing condition. 

c. 

Moderate

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 The rate of ice accumulation requires frequent cycling of manual deicing systems to minimize 

ice accretions on the airframe. A representative accretion rate for reference purposes is 1 to 3 inches (2.5 to 7.5 

cm) per hour on the unprotected part of the outer wing. The pilot should consider exiting the icing condition as 

soon as possible. 

d. 

Severe

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 The rate of ice accumulation is such that ice protection systems fail to remove the accumulation 

of ice and ice accumulates in locations not normally prone to icing, such as areas aft of protected surfaces and 

any other areas identified by the manufacturer. A representative accretion rate for reference purposes is more than 

3 inches (7.5 cm) per hour on the unprotected part of the outer wing. By regulation, immediate exit is required. 

Note: 

Severe icing is aircraft dependent, as are the other categories of icing intensity. Severe icing may occur at 

any ice accumulation rate when the icing rate or ice accumulations exceed the tolerance of the aircraft. 

PCG I

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