ADS-B Out and ADS-B In Explained

ADS-B (Automatic Dependent Surveillance – Broadcast) is the standard surveillance system for the majority of the world’s aviation industry. And, as of 2020, ADS-B Out is mandatory for aircraft flying through a number of countries’ airspace, including in the US, Europe, Canada and large parts of Asia/Pacific.

Let’s dig deeper into these two reception modes and explain the differences between them in more detail.

What is ADS-B Out?

ADS-B Out refers to an aircraft’s ability to broadcast its position, and other information to receivers, either on the ground or in other aircraft. Aircraft operating with ADS-B Out require a Mode S transponder and Extended Squitter to be enabled. At the other end, for the data to be received by air traffic controllers, ground receivers require an antenna with receiver, and an adapted surveillance processor.

ADS-B Out/In infographic

An aircraft with ADS-B Out is able to broadcast information about its GPS location, altitude, speed and other data, to enable efficient tracking of the aircraft. It works by sending two different message sets via the 1090MHz frequency (also via 978Mhz in the US, for aircraft flying under 18,000 FT MSL) to receiving stations on the ground, and to onboard receivers on other aircraft.

What is ADS-B In?

ADS-B In allows the receiving of broadcasts from other aircraft which helps to give pilots better situational awareness, and enables self-separation of aircraft. Unlike ADS-B Out, ADS-B In is not mandatory – it depends on the categories of aircraft and also on airspaces.

It also enables aircraft to receive broadcasts and data from the ground network, such as information about traffic (TIS-B) and weather (FIS-B). It also allows the receiving of broadcasts from other aircraft.


Whilst ADS-B In is not mandatory, it does contribute greatly to safety. This was demonstrated in a study looking at operations and accident data between 2013-2017. It showed that accident rates reduced between 40-60 percent for aircraft equipped with ADS-B In.

To have ADS-B In capability, an aircraft needs to be equipped with an ADS-B receiver, ADS-B data processing and a cockpit display for pilots to view the information being received.

To fully utilize ADS-B In capabilities, the aircraft needs to leverage  ADS-B Out as well, so as to receive information. Without it, aircraft can ‘piggy back’ off other aircraft in the area receiving TIS-B services, but will only receive a partial picture of the traffic as the exact location isn’t known. Aircraft without ADS-B In can also receive traffic and weather information via a portable wireless receiver, such as Stratus.

What are the regulations for ADS-B?

ADS-B Out is only mandatory for aircraft flying within certain airspace. For example, in the US the requirements are as follows:

  • Class A airspace where Instrument Flight Rules (IFR) flights only are permitted
  • Class B and Class C airspace where IFR and Visual Flight Rules (VFR) flights are permitted
  • Certain areas of Class E airspace where IFR and VFR flights are permitted, and all flights receive traffic information where practical, but only IFR flights are provided with air traffic control service, and separated from other IFR flights
  • Within 30 nautical miles of certain major US international airports

Airspace Requirements for ADS-B
Note: The above regulations are for the US only.

ADS-B In is not mandatory, but for operators who choose to equip their aircraft with these avionics, it’s necessary to install a compatible display for the pilots to see all the necessary information. For any aircraft operating internationally, from 2020 it is essential for them to be equipped with ADS-B Out, and this is likely to become the standard surveillance technology globally.

How can Spire help with ADS-B data requirements?

Spire is a provider of global flight tracking data. We offer access to both historical and up-to-date flight and weather data to support aviation operations. Our satellite-based receivers enable us to capture data, via ADS-B signals, in remote areas that terrestrial data services cannot, such as large bodies of water or mountain ranges. This means we can provide more complete global coverage, 24/7.

Having access to more data means Spire customers can make more strategic business decisions, faster. With our flight tracking and historic data APIs, you can quickly integrate and query data into your workflows.

For more information about how Spire can help with your business needs, just give us a shout.

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Continue reading our ADS-B series

01: How ADS-B has Shaped the Modern Aviation Industry
02: How does ADS-B work?
03: What is ADS-B tracking?
Current: ADS-B Out and ADS-B In Explained
05: ADS-B data: understanding basic regulatory context

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