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 or large supercooled water droplets. 

c. Mixed- A mixture of clear ice and rime ice. 

Intensity of icing: 

a. Trace- Ice becomes perceptible. Rate of accumulation is slightly greater than the rate of sublimation. Deicing/anti-icing equipment is not utilized unless encountered for an extended period of time (over 1 hour). 

## I 

b. Light- The rate of accumulation may create a problem if flight is prolonged in this environment (over 1 hour). Occasional use of deicing/anti-icing equipment removes/prevents accumulation. It does not present a problem if the deicing/anti-icing equipment is used. 

c. Moderate- The rate of accumulation is such that even short encounters become potentially hazardous and use of deicing/anti-icing equipment or flight diversion is necessary. 

d. Severe- The rate of ice accumulation is such that ice protection systems fail to remove the accumulation of ice, or ice accumulates in locations not normally prone to icing, such as areas aft of protected surfaces and any other areas identified by the manufacturer. Immediate exit from the condition is necessary. 

Note: 

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.) 

IDENTIFICATION [ICAO]- The situation which exists when the position indication of a particular aircraft is seen on a situation display and positively identified. 

## IF- 

(See INTERMEDIATE FIX.) 

IF NO TRANSMISSION RECEIVED FOR (TIME)- Used by ATC in radar approaches to prefix procedures which should be followed by the pilot in event of lost communications. 

(See LOST COMMUNICATIONS.) 

## IFR- 

(See INSTRUMENT FLIGHT RULES.) 

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. 

