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Identification, friend or foe (IFF) is a combat identification system designed for command and control. ... (12 bit) identification code for the aircraft, assigned by ...
Discrete 1200 series codes unless otherwise allocated (for example, 1255), designated for DVFR aircraft and only assigned by a flight service station. [3] 1255 US: Aircraft not in contact with an ATC facility while enroute to/from or within the designated fire fighting area(s). [3] [11] 1273–1275 US
A discrete transponder code (often called a squawk code) is assigned by air traffic controllers to identify an aircraft uniquely in a flight information region (FIR). This allows easy identification of aircraft on radar. [6] [7] Codes are made of four octal digits; the dials on a transponder read from zero to seven, inclusive. Four octal digits ...
Provides 2-digit 5-bit mission code (cockpit selectable) [1] 2: Provides 4-digit octal unit code (set on ground for fighters, can be changed in flight by transport aircraft) [1] 3: A: Provides a 4-digit octal identification code for the aircraft, set in the cockpit but assigned by the air traffic controller.
Mode 4 is used by military aircraft for the Identification Friend or Foe (IFF) system. Mode S is a discrete selective interrogation, rather than a general broadcast, that facilitates TCAS for civilian aircraft. Mode S transponders ignore interrogations not addressed with their unique identity code, reducing channel congestion.
The Gillham interface and code are an outgrowth of the 12-bit IFF Mark X system, which was introduced in the 1950s. The civil transponder interrogation modes A and C were defined in air traffic control (ATC) and secondary surveillance radar (SSR) in 1960. The code is named after Ronald Lionel Gillham, a signals officer at Air Navigational ...
To help identify individual aircraft, ground operators would tell the aircraft to set their IFF to a particular Mode, and then select a two-digit code on the SIF box. In Mode 3, all 64 responses (00 to 77) were possible, but in Mode 1, the second digit was only 0 to 3, for a total of 32 codes.
Secondary surveillance radar antenna (flat rectangle, top) mounted on an ASR-9 primary airport surveillance radar antenna (curved rectangle, bottom).. The need to be able to identify aircraft more easily and reliably led to another wartime radar development, the Identification Friend or Foe (IFF) system, which had been created as a means of positively identifying friendly aircraft from unknowns.