Is ACAS Compulsory in Business Aviation?

Having provided an outline of Airborne Collision Avoidance Systems (ACAS) and considered how it is developing in Business Aviation, Ken Elliott explores what the ACAS/TCAS-related mandates stipulate in different parts of the world…

Ken Elliott  |  26th April 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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    TCAS II was originally required by all International Civil Aviation Organization member states for turbo-powered airplanes with a maximum take-off weight (MTOW) of more than 15,000kg, or authorized to carry more than 30 passengers in 2003.

    The mandate was extended in 2005 for turbo-powered airplanes with a maximum take-off weight of more than 5,700kg or authorized to carry more than 19 passengers.

    FAA (United States): For Business and General Aviation, Part 135 and Part 91K operations require TCAS, if the aircraft is turbine powered and carries 10-30 passengers.

    Although voluntary, if installed and operated under Part 91 operations, the TCAS must be at least version 7, developed under TSO-C119 and operated under Part 91.221.

    Eurocontrol: The carriage of ACAS II is mandatory for all civil fixed-wing turbine-engine aircraft having a maximum take-off weight exceeding 5,700kg or a maximum approved passenger seating configuration of more than 19 passengers.

    For new aircraft, ACAS II version 7.1 was required from March 2012, whereas for aircraft already equipped with TCAS II version 7.0, version 7.1 was required from December 2015.

    Mexico: Commercial operators with an MTOW greater than 12,500lbs or authorized to transport more than 19 passengers were required to equip with ACAS/TCAS II Version 7.1 or higher by January 1, 2022.

    TCAS in the Minimum Equipment List (MEL)

    Aircraft have lists of minimum functional equipment for each flight, listed under an MEL. The MEL requirement regarding TCAS is:

    • Flying with an inoperative ACAS II is permitted provided it is done in accordance with the provisions of the MEL.
    • In most airspace regions a TCAS fault must be rectified within ten days or less.

    TCAS Standards & Certification

    As with all avionics, standards were (and will continue to be) developed for ACAS. The standards are developed by the US, Europe and ICAO, and adopted by national airworthiness authorities across the world.

    US-based RTCA hosts industry and governing authorities to develop the initial design standards that later translate into Technical Standard Orders (TSO) for design and manufacturing, and Airworthiness Circulars (AC), as integration and operating requirements.

    The installation of TCAS, developed and built under a TSO is governed by an AC and integrated under a Type Certificate for new, and Supplemental Type Certificate for aftermarket aircraft.

    Service Bulletins or Aircraft Service Changes are used for revisions of software and hardware. Once installed or revised the correct version of Flight Manual Supplement must be included.

    Table B: Standards Developed in the US & Europe for Different Versions of ACAS

    Hybrid Surveillance Standards

    Hybrid Surveillance should meet the Minimum Operational Performance Standards (MOPS) document RTCA/DO-300. This version of surveillance is also included as optional functionality within FAA TSO-C119c. China has issued version CTSO-C119e, and Europe ETSO-C119e for the same purpose.

    Summary

    TCAS I and II have been around in Business Aviation since the 1990s, and while mandated earlier this century have not undergone major changes other than to version 7.1. Flight crews know what to expect from TCAS, and in consideration of that upcoming ACAS-Xa versions will be somewhat seamless in their operation.

    What will differ soon is the software and processing behind the scenes, taking advantage of faster and greater capabilities.

    Other versions of TCAS, able to fit into small drones and urban transportation, will develop in parallel to provide game-changing features that accommodate unusual trajectories, rapid closure rates and close-proximity maneuvering.

    As the density of traffic increases across the planet, safe operations become harder to sustain, so Artificial Intelligence (AI) will play its part in layering thousands of aircraft conflict scenarios, introduced as software onto open architecture platforms.

    With more collision possibilities to contend with, it will take a lot of simulation and testing to develop the appropriate responsive programs.

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