An Overview of ADS-B in the Flight Deck

Because of recent equipage mandates, many operators will be familiar with ADS-B, and especially ADS-B Out. But there’s much more to understand about its background, technology and future, as Ken Elliott highlights...

Ken Elliott  |  29th May 2023
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    Ken Elliott
    Ken Elliott

    Ken Elliott is a veteran with 52 years of aviation experience, focussed on avionics in General and Business...

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    An overview of ADS-B in Business Aviation


    In 1997 the FAA and partners initiated the Capstone Project in Alaska to improve situational awareness and safety in areas with limited infrastructure and insufficient ground radar coverage. The goal was to enable Air Traffic Control (ATC) to ‘see’ traffic.

    General aviation aircraft were outfitted with new equipment, including an integrated GPS, Universal Access Transceiver (UAT) and Flight Information System (FIS) for weather information. This early integration of surveillance technologies became ADS-B (Automatic Dependent Surveillance - Broadcast).

    Importantly this version of ADS-B relied on a cockpit display, so not only could ATC see traffic but so could the flight crew on each equipped aircraft. The display of other traffic was all-important to aircraft flying in the remote Alaskan skies.

    Later the Capstone Project was expanded into the Gulf of Mexico to assist oil rig traffic that also could not be sufficiently supported by ground radar.

    As ADS-B developed and it was realized how significant a role it could play in multiple regions, future requirements were outlined. Along came ADS-B Out and ADS-B In, separating the general broadcast of information off the aircraft with an ability for each to independently monitor other traffic.

    Ultimately, ADS-B Out became a requirement for most operators and ADS-B In remains an option. To this day, light aircraft exceed all other aircraft groups in embracing ADS-B In while there remains no official standard as to ADS-B In display requirements.

    ADS-B – A General Description

    Although ADS-B relies on active transponders, it is a passive technology with a surveillance window open to just about anyone with the ability to view its results.

    For a long time Transponders and Flight Management Systems (FMS) operated independently, but with ADS-B the two rely on each other to place nearby equipped aircraft alongside others in a moving navigation display of surrounding airspace.

    What is ADS-B, and why ‘Out’?

    Automatic: Without the need to be interrogated by ground radar, aircraft can independently and automatically broadcast their Global Positioning System (GPS) position along with other useful information.

    Dependent: Indicates a reliance on technologies and information provided by onboard aircraft systems, such as Wide Area Augmentation System (WAAS), GPS and transponders. Surveillance: Implies the passive monitoring of neighbouring activity within a defined 3D airspace.

    Broadcast: Implies the general radiation of information (as opposed to being directed at a specific party).

    Out: Refers to an aircraft sending its ID, position and intention to ATC and other aircraft. But there is a catch: other aircraft must have ADS-B In capability to see anything during flight. Meanwhile, Traffic Collision Avoidance Systems (TCAS) and Terrain Awareness & Warning Systems (TAWS) take care of critical aircraft and terrain avoidance respectively, with TCAS showing target aircraft within its performance range.

    Additional Capability in Specific Airspace Regions

    ADS-B using an 978MHz Universal Access Transceiver (UAT) must be able to function as Class A, while transmitting and receiving (ADS-B Out and In) ADS-R, TIS-B and FIS-B, or as Class B (transmitting ADS-B Out only).

    ADS-B using 1090MHz Extended Squitter Transponders must be able to function as Class A, transmitting and receiving (ADS-B Out and In) ADS-R and TIS-B, or as Class B, transmitting ADS-B Out only.

    With an ADS-B In display, aircraft transmitting on 1090MHz can receive both 978 and 1090MHz broadcasting aircraft. Most ADS-B operations outside of the US operate on 1090MHz frequency. Limited 978MHz capability has been provided outside of the US.

    What are ADS-R, TIS-B and FIS-B Free Services?

    ADS-R: An FAA rebroadcasting service operating at or below 24,000ft (FL240), ADS-R allows aircraft on 1090MHz to see other aircraft operating on 978MHz and vice-versa at up to a 15nm range.

    TIS-B: With TIS-B, at or below 24,000ft (FL240) aircraft with ADS-B In may receive ADS-B, ATC ground radar targets of air traffic, and – when available – surface traffic on their cockpit displays.

    FIS-B: An FAA service only available to aircraft operating on 978MHz and with ADS-B In (typically light General Aviation aircraft), FIS-B provides a comprehensive weather and aeronautical information service.

    ADS-B Version 0, 1 and 2

    As with any technology the introduction of ADS-B was undertaken in phases, with necessary improvements introduced along the way.

    Version 2 was developed to provide improved performance and additional information after learning experiences with earlier versions. Version 2 includes a tie-in with TCAS II’s Resolution Advisory feature.

    Having set out this introduction to what ADS-B is, Ken Elliott sets out how it works in different regions of the world, and reviews the technology behind ADS-B. Read about this in the May AvBuyer digital edition, or continue reading online by clicking the Page 2 button below…

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