Automatic dependent surveillance – broadcast (ADS–B)

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Automatic dependent surveillance – broadcast (ADS–B)

Automatic dependent surveillance-broadcast (ADS–B)


Do you know how those flight tracking websites are functioning? If not. Don’t worry, we are going to do a full analysis of the technology behind those flight tracking websites.

First, we should have a look at the aircraft and associated equipment. As we all know each and every modern commercial aircraft is equipped with an equipment called Transponder and it assists two systems in the aircraft. They are ATC system and the TCAS system. TCAS stands for Traffic alert and Collision Avoidance System and it helps to detect and alert the pilots about traffic vicinity to the aircraft.

TCAS system consists of two antennas, one at the top of the fuselage and the other at the bottom of the fuselage. They transmit at 1090 MHz and receive at 1030 MHz and their range is normally about 30 NM. These signals are transmitted from the TCAS antenna by creating a virtual sphere where it’s radius is 30 NM and alert pilots if there are intruders to this sphere. As mentioned previously these signals do not travel a long distance to reach the earth.

When it comes to ATC system they have normally four ATC antennas. Two of them are located at the lower nose fuselage and other two at the upper nose fuselage. Even these antennas transmit and receive at 1090 MHz and 1030 MHz respectively. These signals used for ATC purposes, hence they should reach the earth. Pilots and air traffic controllers use these signals to exchange information between the aircraft and the control center. These signals contain a lot of information about the aircraft including airspeed, altitude, destination, number of passengers and so on.

These 1090 MHz signals can be received by two kinds of receivers in the earth,

  1. Secondary Surveillance Radar(SSR) and
  2. ADS-B Receivers

Secondary Surveillance Radar is used by air traffic controllers for air traffic management purposes and the information receiving from the signal can be decoded to present in a monitor.

For our purpose, we want to equip with an ADS-B receiver and it performs the same function as SSR except the fact that this receiver can’t transmit signals. Signals coming from the aircraft ATC antennas are received by this receiver and subjected to a decoding process. By decoding the signals it is possible to get real-time data about the aircraft. This decoded information is then uploaded to the server of a particular website. Those flight tracking websites have a system of vast ADS-B receivers located all around the world. Hence they are receiving information all around the globe depending on their coverage. By combining the data from receivers and flight plan data from the airliners they show the real-time traffic of all the aircraft around the globe.

This is how a flight tracking website is functioning and it is a c

For more understanding: Pilots and ground personnel can communicate in mainly 3 ways, one method is described above, by using ATC antennas. In this ATC communication either pilot or the controller do not use voice and this is a fully automatic method running on the computers. VHF 1, VHF 2, HF 1 and HF 2 antennas are normally used for voice communication (VHF 3 is dedicated to data communication). These communications can be done through the Audio Control Panel(ACP) and this is the second method that the pilots and controllers can communicate with each other. The third method is CPDLC(Controller Pilot Data Link Communication) and for this, we can use either VHF, HF or SATCOM.

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