Airborne Collision Avoidance Systems for Crewed & Uncrewed Aircraft

Sealevel Systems discusses airborne collision avoidance systems (ACAS), a crucial component of modern aviation, looking at the different types and characteristics.

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Generally, ACAS systems enhance the situational awareness of pilots by actively monitoring the airspace around an aircraft, assessing potential collision threats, and providing guidance to avoid those threats. 

There are several different types of ACAS, but all such systems share a few major characteristics. ACAS systems monitor the airspace around an aircraft and warn pilots of any other aircraft or terrain features in the immediate vicinity. ACAS systems make use of the transponders that are required in all aircraft.

Transponders are devices that produce a response when receiving a radio-frequency interrogation and are used by air traffic control radar to identify aircraft. ACAS systems utilize these transponders and provide collision avoidance protection for a broad spectrum of aircraft types. Another of the major characteristics shared by ACAS systems is that they operate independently of ground-based air traffic control.

While ACAS systems drastically reduce the risk of mid-air collisions, they do not protect against aircraft that do not have an operating transponder. The use of transponders is a well-established aviation safety practice throughout the world, and intentionally disabling a transponder is a serious violation of aviation regulations and can result in severe consequences.

That said, there are scenarios in which transponders are deactivated. These scenarios range from the innocuous, such as during maintenance or testing, or a transponder malfunction, to more deliberate or aggressive, such as during combat missions, or in the process of illegal activities. However, in cases where a transponder has been disabled or has malfunctioned, some emerging technologies seek to perform the same tasks as ACAS without the use of transponders.

In the article, Sealevel also explores: 

• Automatic Dependent Surveillance Broadcast (ADS-B)
• Automatic Dependent Surveillance-Contract (ADS-C) 
• FLARM and Portable Collision Avoidance Systems (PCAS) 
• Radar and sensor systems
• The future of ACAS for crewed and uncrewed aircraft