AS9120B, ISO 9001:2015, and FAA AC 0056B ACCREDITED

Airbound Traffic- ACAS and TCAS

Congested airfields create dangerous flying conditions for pilots and passengers, alongside airplanes, helicopters, and drones that take to the sky in large numbers each day. The skies tend to be packed above metropolitan areas which is where the majority of people live. Airbound traffic can be hazardous, so to ensure safe skies for all aircraft, airborne collision avoidance systems (ACAS) are employed.

 An ACAS is an electronic system meant to monitor aircraft in flight. Traffic collision avoidance systems (TCAS) have long been used in military and commercial aircraft, though they were initially too costly for use in general aviation. These systems, known also as “fishfinders,” were designed to serve as a final preventative measure, not to be used as a first line of defense.

Both TCAS and ACAS systems track radar beacon signals emitted from transponders on planes. The transponder is meant to broadcast a coded identifying signal specific to each aircraft. In order to understand the importance of a transponder, it is important to know that flights manned by humans follow visual flight rules (VFR) or instrument flight rules (IFR). The majority of commercial air transportation is conducted under instrument flight rules which means that every flight under this plan is issued a unique transponder identification code called the “squawk.” This unique four-digit code is assigned based on the location and direction of departure, among other factors. When the aircraft has taken flight, crew members press a button that illuminates the aircraft on the radar belonging to Air Traffic Control. On the other hand, VFR flights do not involve squawking and do not require a transponder unless they are flying within thirty miles of a major airport.

Depending on their application, there are different kinds of ACAS; human-crewed aircraft currently use the version called ACAS II and TCAS II, while unmanned aerial systems (UAS) are employed by the military and contractors. ACAS II is constructed to work independently of other systems in aircraft, and it provides two different alert types: traffic advisory (TA) and resolution advisory (RA). First, a TA alerts pilots to the fact that the aircraft is within an area and on a projected flight path which is dangerous. On the other hand, RA suggests the next course of action the plane should take to remain safe. This technology has progressed significantly since its introduction in World War II, but it should be noted that both aircraft have to possess a transponder and be squawking in order to function. ADS-B Out is a cheap technology that is replacing more expensive transponders, and it is known to offer information that can be accessed by anyone with a smartphone like: traffic location, altitude, and speed.

Overall, ACAS are beneficial because they help prevent collisions, but they do not protect against unmanned aerial systems or drones. The only rule regulating drones is that they must always be flying under 400 feet; this is not necessarily helpful to aircraft because they are often at this height during takeoff and landing. Sharing air space between aircraft and drones is a challenge to this day.

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August 9, 2022

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