ADS-B OUT is a surveillance technology that allows suitably equipped aircraft to broadcast their identity, precise location and other information derived from the relevant on-board avionics systems (such as GNSS and pressure altimeters) through a ADS-B modified Mode S Transponder to ATC (Air Traffic Control). Aircraft that are equipped with ADS-B IN will be able to receive this information to provide situational awareness and allow self-separation. ADS-B transponders get their positions from the GNSS constellation (GNSS, i.e. GPS, Galileo). Simultaneously they broadcast their own positions and other data to any aircraft or ground station equipped to receive it. Unlike radar technology, ADS-B accuracy does not degrade with range, atmospheric conditions or target audience. It is also able to update the ATC situation display more frequently than a traditional radar.


As of 9 October 2018 the IOMAR understands that:

  • Effective 1st January 2019, ADS-B-OUT will be mandatory on most PBN routes in Indian continental airspace at or above FL290. For further details please read this Indian AIP supplement.
  • Effective 1st January 2020, ADS-B OUT will be mandatory for aircraft to fly in most controlled airspace in US National Airspace refer to the FAA link below for specific conditions.
  • Effective 7th June 2020, ADS-B OUT will be mandatory for all aircraft operating IFR/GAT in European airspace that have a maximum take-off mass exceeding 5,700 kg or have a maximum cruising true airspeed capability greater than 250 knots - refer to the EASA and Eurocontrol links below for specific conditions.

For all other current and future mandated airspace, please refer to the relevant authority in each State in whose airspace you intend to operate.

An ADS-B OUT mandate is established by a State which requires to enhance and extend the surveillance of their ATC systems, requiring all aircraft operating in the specific mandated airspace under their control to have a certified GPS position source and a transponder capable of transmitting data from the aircraft without input from the pilot or a request from ATC.

What is ADS-B OUT? ADS-B OUT is a surveillance technology that allows suitably equipped aircraft to broadcast their identity, precise location and other information

Automatic –The signal is always transmitting and requires no use input.

Dependant – Because it relies on on-board systems to provide surveillance information via the satellite system to other parties.

Surveillance – The system provides surveillance – similar to radar.

Broadcast – Because the data including aircraft position, velocity and direction is broadcast to an ADS-B ground station– and the originating source has no knowledge of who receives the data and there is no interrogation or two way contract.

ADS-B replaces or supplements radar surveillance of aircraft.  This new system provides ATC with more precise and accurate position data for aircraft, potentially allowing more aircraft to operate in a smaller area with no reduction in safety margins. Consequently aircraft may be able to fly more direct routes, saving time, reducing fuel consumption and emissions.

Aircraft equipped with an ADS-B transmitter use GPS technology to determine the position of the aircraft and then this position is broadcast, along with the aircraft identification,  altitude and velocity information in real time. This is known as “extended squitter”.  Air traffic control systems receive this flight data and are then able to position and separate aircraft with improved precision and timing.

ADS-B is key to both the Single European Sky (SES) and United States Next Generation Air Transport System (NextGen) performance objectives and by introducing ADS-B in to the surveillance infrastructure provides improved features which will include;

  • Surveillance from ‘gate to gate’
  • Surveillance data provided directly from the on-board systems
  • Improved safety due to more accurate position reporting
  • Improved visibility for ATC
  • Increased capacity in handling aircraft in congested airspace
  • Cost efficiency
  • Improvement of environment sustainability – reduction in CO2 emissions
  • Reduced RF pollution
  • Enhanced use of optimal flight levels
  • Diminishing vulnerability to human errors
  • Provision of air traffic control in remote areas
  • Global Interoperability – using the 1090 MHz Mode S Extended Squitter technology world wide- note at local or regional level other data link technologies can be considered, e.g. UAT system in the USA which uses 978 MHz for operation under 18,000 feet.

A 1090 MHz Mode S extended squitter transponder combined with a certified GPS navigational source such as WAAS GPS. ABS-B relies on a high-integrity GPS navigation source and a data link (ADS-B unit).  There are several types of certified ADS-B data links, but the most common ones operate on 1090 MHz, which is a modified transponder (transponder with an extended squitter), e.g. Transponder upgrade to ADS-Bv2 (ED102A/DO260B) and low latency GNSS receiver transponder wiring.

ADS-B ground stations are line-of-sight facilities. The ability for a ground station to received ADS-B data from an aircraft depends on altitude, distance from the site and obstructing terrain.

When operating outside of radar coverage, ADS-B derived ATS surveillance services may be provided to operators of aircraft that are ADS-B Out enabled, whilst within the coverage volume of commissioned ADS-B ground stations. ADS-B ground stations are significantly cheaper to install and operate compared to primary and secondary radar systems used by ATC for aircraft separation and control. ADS-B ground receivers are currently used but space based ADS-B is currently in development.

Wide Area Multilateration (WAM) is a Next Generation Air Transportation System (NextGen) surveillance capability that enables air traffic controllers to track aircraft flying into and out of airports in areas with limited radar coverage.

WAM provides surveillance through a network of small sensors deployed in remote areas. WAM sensors are inexpensive compared to multi-million dollar radar installations and much easier to install around airports in remote areas and even on mountain tops. A half-dozen sensors can cover a wide swath of previously unobserved airspace.

The sensors send out signals that interrogate aircraft transponders which, in turn, transmit a response. Computers analyse those responses and calculate the precise location of aircraft using time-difference-of-arrival techniques. The aircraft’s position and identification information are then transmitted to air traffic controllers, who use the surveillance data to safely separate aircraft.