INFORMATION CODING IN AIRCRAFT TRANSPONDERS

Prepared byBildiukevych Aleksandr

IAN 309

TRANSPONDER

A transponder (short-for transmitter-responder and sometimes abbreviated to XPDR, XPNDR, TPDR or TP) is an electronic device that produces a response when it receives a radio-frequency interrogation. Aircraft have transponders to assist in identifying them on air traffic control radar; and collision avoidance systems have been developed to use transponder transmissions as a means of detecting aircraft at risk of colliding with each other.

Cessna ARC RT-359A transponder and Bendix/King KY197 VHF communication

radio

SQUAWK

Air traffic control units use the term "squawk" when they are assigning an aircraft a transponder code, e.g., "Squawk 7421". Squawk thus can be said to mean "select transponder code" or "squawking" to mean "I have selected transponder code xxxx“.

The use of the word "squawk" comes from the system's origin in the World War II identification, friend or foe (IFF) system, which was code-named "Parrot".

TRANSPONDER CODES Transponder codes are four digit numbers

transmitted by the transponder in an aircraft in response to a secondary surveillance radar interrogation signal to assist air traffic controllers in traffic separation. A discrete transponder code (often called a squawk code) is assigned by air traffic controllers to uniquely identify an aircraft. This allows easy identification of aircraft on radar.

Squawk codes are four-digit octal numbers; the dials on a transponder read from zero to seven, inclusive. Thus the lowest possible squawk is 0000 and the highest is 7777. Four octal digits can represent up to 4096 different codes.

EMERGENCY CODES

There are three worldwide codes, which used for notification of ATC about emergency situation on board.7700 – Emergency (SOS, MAYDAY);7600 – Radio Failure (Lost Communications);7500 – Aircraft hijacking;

SECONDARY SURVEILLANCE RADAR Secondary surveillance radar (SSR) is referred to as "secondary", to

distinguish it from the "primary radar" that works by passively reflecting a radio signal off the skin of the aircraft. Primary radar determines range and bearing to a target with reasonably high fidelity, but it cannot determine target elevation (altitude) reliably except at close range. SSR uses an active transponder (beacon) to transmit a response to an interrogation by a secondary radar. This response most often includes the aircraft's pressure altitude and a 4-digit octal identifier.

AVIATION TRANSPONDER INTERROGATION MODES In its simplest form, a "Mode" or interrogation

type, is generally determined by pulse spacing between two or more interrogation pulses. Various modes exist from Mode 1 to 5 for military use, to Mode A, C and Mode S for civilian use.

ADS-B TRANSPONDER Automatic dependent surveillance –

broadcast (ADS–B) is a cooperative surveillance technology in which an aircraft determines its position via satellite navigation and periodically broadcasts it, enabling it to be tracked. The information can be received by air traffic control ground stations as a replacement for secondary radar. It can also be received by other aircraft to provide situational awareness and allow self separation.

ADS–B is "automatic" in that it requires no pilot or external input. It is "dependent" in that it depends on data from the aircraft's navigation system.

THEORY OF ADS-B OPERATION

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