As discussed in the Simple Explanation of What is ADS-B, ADS-B serves ground-to-air and air-to-air surveillance purposes, while TCAS is solely utilized for air-to-air collision avoidance. Therefore, when comparing TCAS and ADS-B, the focus is on the distinctions relevant to air-to-air applications.
1. TCAS and ADS-B operate using distinct methods, which can be readily researched online. In simple terms, TCAS functions similarly to an airborne secondary surveillance radar, while ADS-B gathers aircraft information from onboard GPS systems.
2. TCAS and ADS-B serve different applications in aviation. While both technologies enhance pilots' situational awareness by allowing them to "see" other aircraft in their vicinity, TCAS is primarily relied upon for collision avoidance and situational awareness. In contrast, ADS-B offers a broader range of applications beyond collision avoidance, including the ability to support procedures like In-Trail Procedure (ITP).
3. The developmental stages of TCAS and ADS-B differ significantly. TCAS is a well-established technology that has reached maturity, with mandatory installation and usage requirements in civil aviation aircraft. In contrast, while ADS-B has seen widespread adoption for ground-to-air surveillance, its application for air-to-air surveillance remains in the experimental phase. The potential for pilots to rely on ADS-B for executing flight procedures more flexibly and autonomously, as well as using it for collision avoidance and achieving the concept of free flight, represents a future direction rather than a current reality.
4. The onboard equipment for TCAS and ADS-B has similarities and differences. In TCAS, the equipment comprises an interrogator (which transmits interrogation signals at 1030MHz and receives signals at 1090MHz) and a transponder (which receives signals at 1030MHz and transmits signals at 1090MHz). For ADS-B OUT, the equipment consists of a GPS receiver and an ADS-B transmitter (transmitting ADS-B signals at 1090MHz). In contrast, for ADS-B IN, it includes a receiver (receiving ADS-B signals at 1090MHz).
Notably, the TCAS transponder, ADS-B OUT transmitter, and secondary surveillance radar transponder all refer to the same device, the Mode-S transponder.
ADS-B IN is still in the testing phase, and TCAS interrogators are commonly used as ADS-B IN receivers on air carrier aircraft. However, for general aviation aircraft and UAV/drones that lack TCAS onboard, a specific ADS-B IN receiver is utilized, which is not covered in this comparison.