Pilot/Controller Glossary Pilot/Controller Glossary  8/15/19 1/30/20  I  I SAY AGAIN- The message will be repeated.  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).  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:  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.  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.)  PCG I-1  IAF- IAP- ICAO- ICAO 3LD- (See INITIAL APPROACH FIX.)  (See INSTRUMENT APPROACH  PROCEDURE.)  IAWP- Initial Approach Waypoint  (See ICAO Term INTERNATIONAL CIVIL  AVIATION ORGANIZATION.)  (See ICAO Term ICAO Three-Letter Designator) 