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[7] ICAO: Non-discrete mode A code reserved use in mode S radar/ADS-B environment where the aircraft identification will be used to correlate the flight plan instead of the mode A code. [1] US: Used exclusively by ADS-B aircraft to inhibit mode 3A transmission. [3] US: Non-discrete code assignments in accordance with FAA Order JO 7110.65, 5-2.
The aircraft emergency frequency (also known in the USA as Guard) is a frequency used on the aircraft band reserved for emergency communications for aircraft in distress.The frequencies are 121.5 MHz for civilian, also known as International Air Distress (IAD), International Aeronautical Emergency Frequency, [1] or VHF Guard, [1] and 243.0 MHz—the second harmonic of VHF guard—for military ...
Mode 1: military only; provides 2-digit octal (6 bit) "mission code" that identifies the aircraft type or mission. [21] Mode 2: military only; provides 4-digit octal (12 bit) unit code or tail number. [22] Mode 3/A: military/civilian; provides a 4-digit octal (12 bit) identification code for the aircraft, assigned by the air traffic controller.
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 ...
Military mode Civilian mode Description 1: 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 ...
Usually these other frequency bands are only used in oceanic and remote areas, though they work over wider areas or even globally. Military aircraft also use a dedicated UHF-AM band from 225.0 to 399.95 MHz for air-to-air and air-to-ground, including air traffic control communication.
Mode C uses a spacing of 21 μs, and requests the aircraft's pressure altitude, provided by the altitude encoder. Mode 2 uses a spacing of 5 μs and requests the aircraft to transmit its Military identification code. The latter is only assigned to Military aircraft and so only a small percentage of aircraft actually reply to a mode 2 interrogation.
IFF Mark X was the NATO standard military identification friend or foe transponder system from the early 1950s until it was slowly replaced by the IFF Mark XII in the 1970s. It was also adopted by ICAO, with some modifications, as the civilian air traffic control (ATC) secondary radar (SSR) transponder.