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Can TCAS systems on commercial airplanes detect small objects like drones?


The increasing popularity of drones has raised concerns about their potential collision risks with manned aircraft. As a result, there is a growing interest in understanding the capabilities of collision avoidance systems, such as the Traffic Collision Avoidance System (TCAS), in detecting small objects like drones. This article explores the functionality of TCAS systems on commercial airplanes and their ability to detect drones, with relevant examples and insights.


Understanding TCAS

TCAS, which stands for Traffic Collision Avoidance System, is an aircraft collision avoidance system designed to reduce the risk of mid-air collisions between aircraft. It operates independently of air traffic control and uses secondary surveillance radar (SSR) transponder signals to monitor the airspace around an aircraft. TCAS warns pilots of the presence of other transponder-equipped aircraft that may pose a threat of mid-air collision.


How TCAS works?

TCAS Components: For TCAS to function, the aircraft must be equipped with the following components:

  • TCAS: This includes two TCAS antennae and a TCAS computer.
  • Transponder: A working transponder is required in the aircraft.
  • Display System: A proper aural and visual display system is needed to show pilots cautions, warnings, and evasive maneuvers.

Independent Operation: 

TCAS operates independently of the aircraft's navigation equipment and ground-based systems such as ground radar. It functions like a secondary surveillance radar (SSR) by interrogating the transponders of nearby aircraft on the 1030 MHz band. The surrounding aircraft's transponder replies on the 1090 MHz band, providing data such as barometric altitude, range, and relative bearing to the TCAS of the own aircraft.

Constant Communication: The TCAS of the own aircraft and the surrounding aircraft maintain constant communication with their respective transponders. The TCAS tracks the surrounding aircraft by continuously interrogating them and receiving replies. This enables the TCAS to update the relative range and altitude information, which is crucial for its operation.

Collision Threat Evaluation: TCAS calculates the Closest Point of Approach (CPA) and the time to reach the CPA, known as Tau. The CPA represents the point at which the surrounding aircraft is estimated to enter the safe zone of the own aircraft. The TCAS calculates Tau for both horizontal and vertical ranges, evaluating the potential collision threat.

Alerts and Advisories: Based on the calculated threat level, TCAS provides alerts and advisories to the pilots. These alerts can be visual and aural, warning the pilots of the presence of other transponder-equipped aircraft and the potential risk of a mid-air collision. The system may also provide instructions for evasive maneuvers to avoid the collision, displayed on the cockpit screen.

In order for the two planes to avoid mid-air collisions, a TCAS system must be installed in both vehicles.

The specific details and functionalities of TCAS may vary among aircraft and avionics manufacturers, but the overall principles and objectives remain consistent.



Can aircraft fly without TCAS?

Since the early 1990s in the USA and since 2000 in Europe, passenger aircraft cannot fly without a Traffic Collision Avoidance System (TCAS). TCAS is an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between aircraft. It monitors the airspace around an aircraft for other aircraft equipped with a corresponding active transponder, independent of air traffic control, and warns pilots of the presence of other transponder-equipped aircraft that may present a threat of collision.

The TCAS system constantly transmits an aircraft's identifier, along with other information such as altitude, speed, and direction, via radio signals. When an aircraft's TCAS detects a signal from another plane, it initiates a conversation with the other aircraft to determine the distance and potential collision risk.

Given this information, it is clear that TCAS plays a main role in enhancing air safety and reducing the likelihood of mid-air collisions. Therefore, it is not advisable for aircraft to fly without TCAS. TCAS is mandated by the International Civil Aviation Organization (ICAO) for all aircraft with a maximum takeoff weight (MTOW) over 5,700 kg or authorized to carry more than 19 passengers. It is a crucial safety measure that enhances situational awareness and helps pilots take appropriate actions to prevent mid-air collisions.



TCAS and Drone Detection

Traditionally, TCAS was primarily designed to detect and avoid collisions with other manned aircraft. However, the proliferation of drones has prompted the need to assess TCAS capabilities in detecting these smaller unmanned objects.

In recent years, advancements have been made to adapt TCAS systems to detect drones effectively. For example, the development of the Airborne Collision Avoidance System (ACAS) X has aimed to create a universal collision avoidance system for all aircraft types, including drones. ACAS X employs advanced algorithms and equipment to enable the safe integration of drones into shared airspace.

The integration of ACAS X or similar systems into aircraft avionics enables pilots to receive real-time information about the presence and proximity of nearby aircraft, including drones. These systems display symbols on the cockpit screen, indicating the position of other transponder-equipped aircraft, including drones.


While TCAS systems were initially designed to detect and avoid collisions with other manned aircraft, efforts have been made to adapt these systems to detect smaller objects like drones. The development of systems such as ACAS X has introduced advanced algorithms and equipment to enhance the ability of TCAS to detect and avoid potential collisions with drones. Through visual displays and real-time information, pilots can receive timely alerts and take appropriate actions to mitigate the risk of mid-air collisions involving drones.

The specific capabilities and implementations of TCAS systems may vary among aircraft and avionics manufacturers. It is crucial for aviation professionals and stakeholders to stay updated with the latest advancements and regulatory requirements related to drone detection and collision avoidance systems.



 

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