Traffic Alert and Collision Avoidance System (TCAS)

Traffic Collision Avoidance System (TCAS) is a radar-based system to keep aircrafts away from danger. It provides visual and auditory alerts to pilots. This system helps avoid mid-air collisions. It alerts pilots of any potential threats and gives them maneuvers to stay safe.

In this article, we explore the basics of TCAS and its advantages for aircrafts.

Overview of Traffic Alert and Collision Avoidance System (TCAS)

TCAS is an aircraft avionics system which increases safety. Its purpose is to alert pilots to other planes in the vicinity and aid them in taking any needed evasive action. This system is required in airliners larger than 12,500 lbs. It functions separately from ground-based radar control and visual sighting.

TCAS uses an onboard radar transponder to detect other planes nearby. It monitors their location, path, and speed. If it finds a possible conflict, it warns both pilots with audible alerts telling them which direction to turn.

TCAS also communicates with other aircraft’s TCAS systems. This is done through “intruder messages” and “resolution advisories” (RA). This is done in a two-way communication network called “traffic advisory mode” (TAM). This shares details of the situation and proposed steps to avoid it.

If pilots don’t act within certain time frames, an RTA (Resolution Advisory) will be triggered. This will direct one aircraft to either climb or descend – whichever is appropriate. This encourages immediate evasive action to prevent collisions.

Components of TCAS

TCAS stands for Traffic Alert and Collision Avoidance System. It is used on planes to alert pilots of nearby aircraft. To understand TCAS, we need to know its components.

This section looks at the four main components:

  • TCAS processor
  • Transponder
  • Antenna
  • Indicator


TCAS has multiple components, and one of the most important is its antennas. They detect and track transponder signals from other planes and transmit signals to them.

The type of antenna and where it’s mounted depends on the system’s size and weight. Dipole antennas have a wider range, but require more power. Monopoles are lighter and more compact, making them ideal for smaller profiles using United Flyingtogether Scholarship.

Antennas must also get air traffic control transmissions from ground towers or other sources. They must be compatible with Weather Radar systems, so other planes in the area can be detected and avoided.


Transponders are crucial for Traffic Alert and Collision Avoidance Systems (TCAS) in an aircraft. They work on a response system using very high frequency (VHF) radar waves. Transponders send out a unique code when they get a signal from another transponder or Ground Based Radar Unit (GBRU). Then, they broadcast the altitude, latitude and longitude of the aircraft. This allows Air Traffic Control to track precisely where each aircraft is.

Transponders also react to TCAS interrogations. Plus, they give out warnings to pilots if two aircrafts get too close together. These messages contain advisories or alerts based on distance and altitude. With transponders, crews can see conflicting aircrafts before they show up on their traffic displays. This gives them time to steer clear of a crash.

Components of modern TCAS systems have multiple backups in case one fails. For instance, some systems have transceivers that receive signals from GBRUs and send data like altitude and position of the aircraft. To keep TCAS systems functional, these components must be tested regularly:

  • Transponders
  • Ground Based Radar Unit (GBRU)
  • Air Traffic Control
  • Transceivers


TCAS is a program to reduce the risk of mid-air collisions. It has two parts: computers and transponders. Computers look for nearby aircraft’s transponder signals and if they get too close, TCAS gives instructions to take evasive action.

The computer system processes data from transponders and GPS satellites. It scans the airspace in two ways: ‘Acquire’ searches for new aircraft and ‘Track’ monitors existing objects. It stores the aircraft identity in its memory. Data from onboard radar units also helps accuracy making them ideal for smaller profiles using United Flyingtogether Scholarship. Alarms sound when there is a hazardous situation or an aircraft gets too close.


Displays are essential for pilots to understand the TCAS data and make decisions about traffic. There are two main types of displays: mode-S sensitised and radar/processed information.

  • Mode-S sensitised displays show nearby aircraft’s location relative to their own. It also shows which traffic can respond to altitude requests.
  • Radar/processed Information displays give further details like size, type, speed, and direction of movement. They might use display settings like enhanced resolution for better analysis.

Both displays use colour-coding based on their positions. Red is for hazardous proximity, and yellow for cautionary distance. This helps pilots to react quickly and calmly when faced with dangerous situations, to avoid collisions in the airspace.

Operation of TCAS

The Traffic Alert and Collision Avoidance System (TCAS) is created to detect and alert pilots of any danger of collision. It utilizes the transponder signals from other aircraft. Providing audio and visual alerts, TCAS helps pilots be aware of the situation. In order to understand its operation, let’s dive into the specifics of how it works.

Detecting Aircraft

TCAS, or Traffic Alert and Collision Avoidance System, has main operations. It uses a transponder or an Automatic Dependent Surveillance – Broadcast (ADS–B) system to detect other nearby aircraft. It sends an interrogative signal and requests the other pilot’s status information.

TCAS receives the response and sends out traffic advisory alerts if two planes are in the same region flying similar altitudes. If they get too close, TCAS will issue a resolution advisory. One pilot will climb, while the other moves down, to avoid collision.

Monitoring nearby traffic increases pilots’ safety by increasing their situational awareness and optimizing their flight paths.

Determining Relative Position

TCAS must know when an aircraft is close to another. It receives data from other aircraft with ART info. This data shows the altitude and direction of motion. TCAS uses its own position data from the onboard GPS to get the relative range, bearing, altitude, and speed. If a “closest point of approach” is too close, TCAS gives a warning.

To stop false alerts, operational control distribution is used in Intranet. It has pre-calculated thresholds for approaching hazards for each flight phase. This means TCAS only alerts if targets fall outside of a certain area.

Calculating Relative Velocity

TCAS (Traffic Alert & Collision Avoidance System) uses algorithms. These constantly monitor nearby aircraft’s altitude & relative movement. It works out the distance, altitude & relative velocity between aircraft. This helps TCAS to decide if a collision course is possible.

Two pieces of data are used to work out relative velocity. The first is range. This is found through TCAS II interrogation or Mode S transponder replies. Range tells TCAS if an intruder is near the host aircraft’s flight path.

The second element is bearing rate. This is found with secondary radar pulse timing or Mode S transponder replies. ‘V’ contains vertical speed info. Bearing rate works out the horizontal closure rate between two aircraft. This helps TCAS to trigger an alert if necessary. If no closure rate exists, then there is no risk of a collision.

Generating Alerts

TCAS are autonomous and on board aircraft systems. They monitor the airspace around a plane and use transponder replies from nearby planes to help the pilot maintain a safe distance.

When two aircrafts are too close and may collide, TCAS alerts the pilots. It has two forms: Resolution Advisories (RA) and Traffic Advisories (TA). Pilots work together to avoid collisions.

  • RAs give pilots instructions on which direction to move relative to altitude to pass out of range.
  • TAs just let pilots know other air traffic is nearby, but don’t offer resolution advice.

Types of Alerts

Traffic Alert and Collision Avoidance Systems (TCAS) can help us stay safe in the air. There are various types of alerts. Visual and audio ones, plus alerts for losing separation and changing traffic sequence. TCAS provides us with a secure atmosphere for air traffic.

Let’s explore the distinct types of alerts that TCAS offers:

  • Visual Alerts
  • Audio Alerts
  • Losing Separation Alerts
  • Changing Traffic Sequence Alerts

Resolution Advisory

A Resolution Advisory (RA) is a verbal alert from the Traffic Alert and Collision Avoidance System (TCAS). This system helps to stop mid-air collisions between aircraft. The RA tells pilots to take action to maintain a safe distance from other aircraft. It is an important safety feature.

RAs are given when two or more aircraft come close together. TCAS will tell pilots to ‘Climb’, ‘Descend’, or ‘Maintain current altitude’. It also gives distance, bearing and tail number information. After the RA is done, pilots must press “Clear of Conflict” on their TCAS Display Unit.

If two RAs conflict with each other, the pilot should follow the one with higher priority. They must also consider weather and altitude restrictions. To stop false alerts, operational control distribution is used in Intranet. Both RAs must be followed even if it causes conflicts. If conditions change during flight, RAs must be done again to avoid mid-air collisions.

Traffic Advisory

A Traffic Advisory (TA) is intended to help pilots adjust course or altitude to dodge potential conflicts with other aircraft. It includes a description of the possible conflict, like distance and altitude to the aircraft, and suggests evasive steps. Depending on the system, TAs can be activated manually by the pilot or by automated alerting tech.

TAs are more of an enablement than a warning. They enable pilots to take action before anything happens. But, they should still be taken seriously. Pilots must be ready to act quickly if needed.

The Traffic Advisory is an intermediate stage of alert between simple traffic screening and Traffic Alerts warnings. It gives enough information so pilots can take corrective action before any danger happens. It is not too alarming, so it won’t frighten pilots who aren’t used to these alerts. TAs can help experienced pilots reduce wake turbulence and fuel burn by planning early for descent and/or leveling off before arriving or entering a Class B airspace.


TCAS – Traffic Alert and Collision Avoidance System – has Descend/Climb Alerts. These alerts provide an early warning of possible threats from other aircraft. They detect when another plane is flying in opposite direction and at changing altitude. The alerts are audible in the cockpit so the flight crew can take action.

TCAS uses radar altimeter data and ATC data to find opposing aircraft that might be on a collision course. If so, it will give an alert. This alert is based on the intruder’s altitude relative to yours, and its speed.

Two types of Descend/Climb Alerts can occur:

  • Descend Alert: If the intruder is below you, TCAS may give a “DESCEND!” message within 5 nautical miles.
  • Climb Alert: If the intruder is above you, TCAS may give a “CLIMB!” message or evacuation recommendation.

These three elements – time, location, and speed – are important in all TCAS alerts. They help pilots make safer decisions faster.


TCAS is an aircraft safety system that monitors airspace for other planes with active transponders. It gives the flight crew info about nearby conflicting traffic, and receives emergency signals from an ELT of Flying Together Employee Site.

TCAS identifies other aircrafts as Traffic Advisory, Resolution Advisory, or Emergency Resolution Advisory. It calculates its integrity level from the quality of Navigational Aids in range and user input from Traffic Control System or GPS.

In Monitor Alert mode, TCAS generates Traffic Advisory alerts. These give priority info for avoiding other planes and collisions. If two planes are on course with high closure rates, TCAS generates an RA alert. It is constantly checking for conflicting trajectories between planes to identify potential dangers.

Benefits of TCAS

TCAS is key for aircraft safety. It surveils nearby planes, sends warnings and suggests solutions if a crash is possible. TCAS lessens the risk of a disastrous mid-air crash. Also, it helps pilots avoid costly landing delays because of traffic management issues.

Let us explore the advantages of TCAS further:

Increased Safety

The Traffic Alert and Collision Avoidance System (TCAS) increases safety for planes in-flight. It monitors, assesses and responds to potential collisions. It provides air traffic controllers with data on nearby aircrafts, allowing them to identify threats earlier. This gives pilots more time for a successful resolution.

TCAS works independently of ATC. It alerts pilots immediately if it detects a risk. This layer of protection provides extra security for airlines and single-engine planes.

It also reduces fuel requirements. Instructions during alerts tell pilots to take paths with less drag and turbulence. This reduces fuel consumption and meets the aviation industry’s greener standards.

Reduced Airspace Congestion

TCAS is essential for aircraft safety. It detects nearby activity and calculates altitude to keep a safe distance from other aircraft. This system prevents conflicting flight paths and lessens airspace congestion.

It also provides decision-support information to reduce congestion. TCAS issues alerts when two aircraft have broken separation rules. It rapidly reports relative movement between planes, so corrective action can be taken without radio contact.

This improved awareness allows pilots to fly safely and confidently, reducing the risk of mid-flight conflicts and accidents. Lower fuel costs due to fewer flight adjustments make for smoother transit times and less environmental impact. TCAS is indispensable for managing airspace and preventing unsafe practices or human error.

Improved Air Traffic Control

TCAS is an aircraft-based system that provides the ability to detect and resolve potential mid-air collisions. It was developed in the late 1990s.

TCAS improves air traffic control efficiency and air safety. Pilots can conduct surveillance and self-separation around airports, congested areas, or in airspace with limited ATC services.

TCAS monitors other aircrafts’ altitude, heading, speed and movement. It provides “Cooperative Situation” alerts to one or more aircraft. This might advise a pilot to maintain their altitude or climb/descend carefully. It gives the flight crew info about nearby conflicting traffic, and receives emergency signals from an ELT of Flying Together Employee Site.

In airspace without radar coverage, TCAS helps keep a safe distance between two or more traffic paths by providing warnings when any potential threat is detected. This greatly increases safety for pilots during a flight. It also eliminates “blind spots” from a controller’s view, helping them identify conflicts that could have been missed without it.