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Tech specifications of ADS-B

What are the requirements for ADS-B?

Two core avionics components on board the aircraft.

Aircraft Avionics System

Environmental and operational sensors feed into onboard avionics systems

ADS-B enabled Transponder

Pilot controlled computer connected to an ADS-B transmitter/receiver

What is Mode S?

All aircraft carry units within their avionics system called transponders (transmitter and responder). These transponders, at the most basic level, emit a four digit signal that can be controlled via a panel on the instrument panel.

These four digits are assigned by air traffic control. On the radar screen, the controller can see the four digit code alongside the radar return of the aircraft. This enables them to identify the aircraft. The signal is received and ‘interrogates’ the transponder. That number is then returned and known as a ‘Squawk’.

Short for ‘selective’ mode, Mode S transponders allow more information to be sent when the air traffic control radar interrogates the transponder. It sends information on altitude, callsign and squawk code which also enables the Airborne Collision Avoidance System (ACAS) and ADS-B systems to function.

Mode S Extended Squitter (1090ES)

Mode S Extended Squitter extends the functionality of Mode S to include satellite derived GPS coordinates within the outbound transmission. The 1090 refers to the broadcast frequency of 1090MHz.

Typically when regulators mandate for ADS-B equipage this refers to outbound 1090ES which is the International Civil Aviation Organisation (ICAO) international standard. ADS-B inbound is typically optional.

How does ADS-B work?

ADS-B uses the avionics within an aircraft to communicate with GPS satellites in orbit and to transmit data

Data sent from ADS-B equipped aircraft is received and decoded by other aircraft equipped with ADS-B avionics as well as ground receivers. These ground receivers then display this information to air traffic controllers through a display. From this information, they can provide vectoring instructions and organize the skies with more accuracy and more reliable information.

Additionally, other aircraft equipped appropriately can also see the same information providing them with a very good early warning system enhancing their own situational awareness.

ADS-B OUT (Data from the aircraft)

  • Callsign
  • Altitude
  • Heading
  • Position
  • Squawk number
  • Speed

ADS-B In (Data into the aircraft)

  • Weather - via Flight Information Service-Broadcast (FIS-B)
  • Terrain
  • Information - via Traffic Information Service-Broadcast (TIS-B)
  • Traffic

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