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12/2/21 

Pilot/Controller Glossary 

I SAY AGAIN

 The message will be repeated. 

IAF

 

(See INITIAL APPROACH FIX.) 

IAP

 

(See INSTRUMENT APPROACH 

PROCEDURE.) 

IAWP

 Initial Approach Waypoint 

ICAO

 

(See ICAO Term INTERNATIONAL CIVIL 

AVIATION ORGANIZATION.) 

ICAO 3LD

 

(See ICAO Term ICAO Three

Letter Designator) 

ICAO Three

Letter Designator (3LD)

 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

 The accumulation of airframe ice. 

Types of icing are: 

a. 

Rime Ice

 Rough, milky, opaque ice formed by 

the instantaneous freezing of small supercooled 
water droplets. 

b. 

Clear Ice

 A glossy, clear, or translucent ice 

formed by the relatively slow freezing of large 
supercooled water droplets. 

c. 

Mixed

 A mixture of clear ice and rime ice. 

Intensity of icing: 

a. 

Trace

 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

  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

 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

 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. 

IDAC

 

(See INTEGRATED DEPARTURE/ARRIVAL 

CAPABILITY.) 

IDENT

 A request for a pilot to activate the aircraft 

transponder identification feature. This will help the 
controller to confirm an aircraft identity or to identify 
an aircraft. 

(Refer to AIM.) 

IDENT FEATURE

 The special feature in the Air 

Traffic Control Radar Beacon System (ATCRBS) 
equipment. It is used to immediately distinguish one 
displayed beacon target from other beacon targets. 

(See IDENT.) 

PCG I