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Mojave Today
By the People, for the People
FAA Validates Next-Gen Collision Avoidance for Uncrewed Aircraft
Remotely Piloted Aircraft Play Key Role in Testing ACAS X Safety System
Apr. 8, 2026 at 2:00am
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The ACAS X collision avoidance system, with its flexible probabilistic model, represents a major leap forward in managing the increasingly crowded skies of the future.Mojave TodayThe Federal Aviation Administration (FAA) has accelerated the validation of its next-generation collision avoidance logic, ACAS X, using Remotely Piloted Aircraft (RPA) as primary testbeds. This transition represents a fundamental shift from the decades-old Traffic Alert and Collision Avoidance System (TCAS II) to a more flexible, probabilistic model designed to handle the increasingly crowded skies.
Why it matters
The ACAS X family of systems is expected to provide a significant safety increase by reducing unnecessary alerts while providing more effective guidance during actual conflict scenarios. By using RPAs for these high-risk stress tests, the FAA can safely evaluate encounter geometries that would be too dangerous for crewed evaluation flights.
The details
The FAA is gathering unprecedented data on how autonomous systems interact with crewed traffic in the National Airspace System (NAS). ACAS X utilizes a numeric look-up table generated through Markov Decision Process optimization, allowing it to be tailored to specific aircraft types through variants like ACAS Xa, ACAS Xu, and ACAS sXu. During the latest round of testing, RPAs equipped with sensors like AESA radars and ADS-B were subjected to 'blind' encounters with non-cooperative aircraft to evaluate the ACAS Xu system's autonomous 'Resolution Advisory' calculations.
- On April 7, 2026, the FAA confirmed the successful flight test campaigns involving RPAs.
- The testing phase is expected to wrap up later this year, leading to updated Technical Standard Orders (TSOs) that will mandate the phase-out of legacy TCAS in favor of the ACAS X family.
The players
Federal Aviation Administration (FAA)
The U.S. government agency responsible for the regulation and oversight of civil aviation.
ACAS X
The sophisticated successor to the decades-old Traffic Alert and Collision Avoidance System (TCAS II), utilizing a flexible, probabilistic model to handle the increasingly crowded skies.
General Atomics MQ-9B SkyGuardian
A heavy Remotely Piloted Aircraft (RPA) used as a testbed for the ACAS Xu system, equipped with a suite of sensors including AESA radars and ADS-B.
What’s next
As the testing phase wraps up later this year, the FAA expects to issue updated Technical Standard Orders (TSOs) that will mandate the eventual phase-out of legacy TCAS in favor of the ACAS X family.
The takeaway
The FAA's validation of ACAS X, leveraging Remotely Piloted Aircraft as testbeds, represents a significant advancement in aviation safety technology. This flexible, probabilistic model will help manage the increasingly crowded skies of the future, paving the way for seamless integration of crewed and uncrewed aircraft.
