Airbus A320 Surveillance Equipment Complete Guide

Airbus A320 surveillance equipment covers two distinct areas of aircraft operation. The first is the airborne surveillance architecture used for air traffic control and collision avoidance, including Mode S transponders, Automatic Dependent Surveillance-Broadcast (ADS-B), and the Traffic Collision Avoidance System (TCAS). The second is the Cockpit Door Surveillance System (CDSS), which uses video cameras to help the flight crew identify persons requesting access to the flight deck.

These systems share the word surveillance, but they perform completely different jobs. Mode S, ADS-B, and TCAS are part of the aircraft’s ATC and traffic-surveillance environment. The cockpit door surveillance system is a security-related video system.

According to the Airbus A318/A319/A320/A321 Flight Crew Operating Manual (FCOM), the surveillance installation includes two Mode S ATC transponders and a TCAS installation consisting of a TCAS computer, two TCAS antennas, and an ATC/TCAS control panel. The same FCOM separately describes the Cockpit Door Surveillance System as comprising three video cameras and an LCD display on the flight deck rear panel.

Introduction to Airbus A320 Surveillance Equipment

What Is Aircraft Surveillance Equipment?

In the ATC sense, aircraft surveillance equipment allows an Airbus A320 to be identified, tracked, and monitored by air traffic services while also allowing the aircraft to detect and assess nearby transponder-equipped traffic.

The principal surveillance functions include:

• Responding to secondary surveillance radar interrogations.
• Transmitting the assigned transponder code and pressure altitude.
• Providing Mode S selective surveillance capability.
• Broadcasting ADS-B Out information on equipped aircraft.
• Detecting surrounding aircraft through TCAS.
• Displaying traffic information on the Navigation Display.
• Generating Traffic Advisories and Resolution Advisories when required.

The Airbus A320 surveillance architecture depends on information supplied by several other aircraft systems. Position, altitude, heading, speed, and flight-identification data can be supplied by systems such as GPS, ADIRS, the Flight Management System, and the Flight Control Unit.

Why Surveillance Systems Matter for Flight Safety

ATC surveillance and TCAS provide two complementary layers of traffic protection.

Air traffic control uses surveillance information strategically to maintain separation and manage traffic flows. TCAS works independently onboard the aircraft and monitors nearby transponder-equipped traffic for a developing collision threat.

The Airbus FCOM states that TCAS determines information including range, relative bearing, closure rate, and relative altitude when this information is available. It predicts the Closest Point of Approach and uses a time-based parameter known as TAU to determine the level of threat.

If the threat becomes significant, TCAS first generates a Traffic Advisory (TA). If the situation becomes more critical, it can generate a Resolution Advisory (RA) that provides vertical avoidance guidance.

What Is Included in Airbus A320 Surveillance Equipment?

Primary Surveillance Components

The A320 surveillance architecture described in the Airbus FCOM includes:

• Two Mode S ATC transponders.
• One TCAS computer.
• Two TCAS antennas.
• One ATC/TCAS control panel.
• Traffic presentation on the Navigation Display.
• TCAS guidance on the Primary Flight Display.
• ADS-B Out capability on applicable aircraft.

One Mode S transponder is active while the second is available as standby equipment. This provides redundancy at transponder level, although the complete TCAS installation itself is not duplicated because Airbus describes a single-channel TCAS computer.

Supporting Data Sources

ADS-B and TCAS are not isolated systems. They depend on valid information from the aircraft’s navigation and air-data systems.

Depending on aircraft configuration, ADS-B Out can transmit information including:

• Latitude and longitude.
• Horizontal integrity information.
• Ground speed.
• Track.
• Barometric altitude.
• Vertical speed.
• Flight number.
• Emergency status.
• Selected altitude.
• Selected heading.
• Barometric pressure setting.

The Airbus FCOM identifies these parameters as part of the ADS-B Out data set on applicable aircraft.

Understanding the Airbus A320 Transponder

What the Transponder Does

The transponder allows ground surveillance systems to identify and track the aircraft. On the A320 configuration documented by Airbus, two Mode S transponders are installed and the flight crew selects the required unit through the ATC/TCAS control panel.

The transponder can provide aircraft identification, pressure altitude, Mode S surveillance data, and ADS-B Out transmission when the aircraft is equipped for that function.

Mode A, Mode C, and Mode S

Mode A provides the four-digit ATC transponder code. Mode C adds pressure-altitude reporting. Mode S provides selective aircraft addressing and supports more advanced surveillance data exchange.

For modern airline operations, Mode S is particularly important because it supports both TCAS coordination and ADS-B applications.

ATC/TCAS Control Panel

The ATC/TCAS control panel allows the flight crew to select the transponder, enter the assigned code, use IDENT, and manage the TCAS operating mode.

The Airbus FCOM also describes an ATC FAIL indication that illuminates when the selected transponder fails on the applicable panel configuration.

ADS-B on the Airbus A320

What ADS-B Means

ADS-B stands for Automatic Dependent Surveillance-Broadcast.

Automatic means the aircraft transmits surveillance information without the crew initiating each report.

Dependent means the information depends on onboard data sources.

Surveillance describes its role in aircraft monitoring.

Broadcast means the information is transmitted for reception by suitably equipped ground stations or aircraft.

According to the Airbus FCOM, ADS-B Out information is transmitted automatically and continuously without requiring a preliminary interrogation.

ADS-B Out vs ADS-B In

ADS-B Out and ADS-B In are different capabilities.

ADS-B Out broadcasts information about the A320.

ADS-B In allows suitably equipped aircraft to receive ADS-B information from other aircraft or surveillance services.

Airbus documentation identifies Air Traffic Situational Awareness (ATSAW) as a configuration-dependent function that can use ADS-B In information. It should not be assumed that every A320 has ADS-B In or ATSAW capability.

ADS-B and Air Traffic Management

ADS-B gives air traffic management systems access to aircraft-derived position and flight data. Unlike traditional secondary radar surveillance, an ADS-B broadcast does not require each report to be triggered by an interrogation.

From the flight crew perspective, most of this process is automatic. Correct aircraft identification, valid navigation information, and correct transponder configuration are therefore essential.

Traffic Collision Avoidance System TCAS

What TCAS Is Designed to Do

TCAS is an airborne collision-avoidance system that monitors nearby transponder-equipped traffic and determines whether another aircraft represents a collision threat.

The system categorizes traffic according to threat level and can progress from normal traffic information to a Traffic Advisory and then to a Resolution Advisory.

TCAS Components

The Airbus A320 TCAS installation described in the FCOM includes:

• One single-channel TCAS computer.
• Two TCAS antennas.
• Two Mode S ATC transponders.
• One ATC/TCAS control panel.

TCAS uses information received from nearby aircraft transponders to calculate relative traffic geometry.

Traffic Advisories and Resolution Advisories

A Traffic Advisory warns the crew that another aircraft may become a collision threat. Airbus gives a typical TAU value of approximately 40 seconds for a TA.

A Resolution Advisory indicates a more immediate threat and provides vertical avoidance guidance. Airbus gives a typical RA TAU value of approximately 25 seconds. The exact thresholds vary according to altitude and system logic.

The A320 Navigation Display uses different symbols to distinguish traffic:

• Other traffic: white empty diamond.
• Proximate traffic: white filled diamond.
• Traffic Advisory: amber circle.
• Resolution Advisory: red square.

Resolution guidance is presented on the Primary Flight Display.

AP/FD TCAS

Some A320-family aircraft are equipped with AP/FD TCAS. On these aircraft, a TCAS RA can be integrated with Airbus flight guidance.

The FCOM describes AP/FD TCAS as a managed vertical mode that automatically engages when an RA occurs, subject to aircraft configuration and system availability.

AP/FD TCAS should therefore not be assumed to be installed on every A320.

Airbus A320 Surveillance During Flight

Before Start and Taxi

During flight deck preparation, the crew verifies the assigned transponder code and correct flight identification. This is particularly relevant on ADS-B-equipped aircraft because the flight number entered in the FMS can be transmitted as part of the ADS-B data set.

On the ground, Mode S may support airport surface surveillance. The Airbus FCOM states that, on the applicable configuration, when XPDR is selected on the ground the selected transponder operates in the selective aircraft interrogation function of Mode S.

Takeoff, Climb, and Cruise

After departure, the transponder supports ATC tracking while TCAS monitors surrounding traffic.

TA/RA is the normal TCAS operating mode. In this mode, traffic can be displayed on the ND and Resolution Advisory guidance can be presented when required.

Surveillance should not be confused with aircraft-performance calculations. Takeoff surveillance and monitoring functions are separate from calculations involving aircraft weight or takeoff speeds.

Descent and Approach

TCAS logic automatically changes close to the ground.

When TA/RA has been selected, the Airbus FCOM states that the system automatically changes to TA ONLY below 1,000 ft AGL. The system also applies several altitude-dependent inhibitions to specific TCAS functions.

These inhibitions are deliberate parts of TCAS logic and should not be interpreted as a system failure.

Surveillance Messages and Failures

Normal and Advisory Indications

Depending on the traffic situation and display configuration, the crew may see messages such as:

• TA ONLY.
• TCAS: REDUCE RANGE.
• TCAS: CHANGE MODE.

These indications help ensure that significant traffic information remains visible and properly interpreted by the flight crew.

Transponder Failure

The A320 installation described by Airbus includes two Mode S transponders. Failure of the selected transponder can generate the ATC FAIL indication, after which the flight crew follows the applicable ECAM or FCOM procedure.

TCAS Failure

A TCAS failure removes or degrades airborne collision-avoidance capability, but it does not necessarily mean that ATC surveillance capability is lost.

Similarly, ADS-B-derived traffic information must not be considered equivalent to fully functioning TCAS Resolution Advisory capability.

Limits of TCAS Protection

TCAS depends on suitable transponder information from surrounding aircraft.

The Airbus FCOM states that TCAS cannot generate a Resolution Advisory against an intruder that does not report altitude.

TCAS is therefore an important safety layer, but it cannot protect against every possible traffic scenario.

Airbus A320 Cockpit Door Surveillance System

What Is the Cockpit Door Surveillance System?

The Cockpit Door Surveillance System, commonly abbreviated CDSS, is separate from ATC surveillance and TCAS.

According to the Airbus A320-family FCOM for the referenced fleet, the cockpit door surveillance system consists of three video cameras and an LCD display located on the flight deck rear panel. The system allows the flight crew to identify persons before authorizing entry to the flight deck.

This makes cockpit door surveillance a security and access-control function rather than an air traffic surveillance function.

How the A320 CDSS Camera System Works

The three surveillance cameras provide different views associated with the cockpit entrance area.

Airbus describes the following operating logic:

• Camera 1 can be displayed when selected from standby.
• Camera 1 is automatically displayed following an entry request from the cockpit-door keypad.
• Cameras 2 and 3 are displayed together using a split-screen presentation.
• The LCD display has automatic brightness adjustment.
• The flight crew can place the system in standby using the Cockpit Door Video pushbutton.

If no crew action occurs for a defined period, the display returns to standby according to the system logic described in the FCOM.

What the Airbus Documentation Does Not State

The referenced flight crew manuals confirm the presence of three video cameras and the LCD display, but they do not provide enough information to claim that the cameras are HD, infra-red, monochrome, or specifically designed for low-light operation.

The FCOM also does not establish that CDSS footage is recorded or stored in a dedicated recorder.

Claims about camera field of view, camera mount design, recording durability, STC configuration, cabin surveillance, cargo-bay cameras, or integration with IFE would require additional Airbus engineering, maintenance, modification, or operator documentation.

This information is not available in the reference documents.

Cabin Surveillance and Other Video Systems

The documented cockpit door surveillance system should not automatically be described as a general cabin surveillance system.

Its stated purpose is to allow the flight crew to identify a person before granting access to the flight deck. Although the cameras naturally monitor the area associated with cockpit access, the available A320 FCOM material does not support a claim that the same installation continuously monitors the passenger cabin, cargo compartment, or cargo bays.

Likewise, the references do not establish universal cabin surveillance cameras across all Airbus aircraft or all A320-family aircraft worldwide.

Aircraft configuration can differ according to production standard, airline requirements, modifications, and certification status.

Common Misconceptions About Airbus A320 Surveillance Equipment

Does Surveillance Equipment Control the Aircraft?

Mode S and ADS-B do not control the aircraft. TCAS can provide vertical avoidance guidance, while AP/FD TCAS can integrate that guidance with the autoflight system on suitably equipped aircraft.

Is ADS-B the Same as Radar?

No. Radar detects or interrogates an aircraft from an external surveillance station. ADS-B broadcasts aircraft-derived information from the aircraft itself.

Is the Cockpit Door Surveillance System Part of TCAS?

No. TCAS processes transponder information from surrounding aircraft. CDSS processes video images from surveillance cameras around the cockpit entrance.

Are the Cockpit Door Cameras Recording Footage?

The referenced Airbus flight crew documentation describes camera images being displayed to the flight crew but does not establish continuous video recording or storage.

This information is not available in the reference documents.

Does Every Airbus A320 Have Exactly the Same Surveillance Equipment?

No. The Airbus A320 family has been produced over several decades and individual aircraft can differ according to modification status, avionics standard, MSN, operator configuration, and regulatory requirements.

The references used here describe the documented fleet configuration and should not be interpreted as proof that every A318, A319, A320, or A321 worldwide has identical equipment.

Frequently Asked Questions

Key Takeaways

Airbus A320 surveillance equipment is best understood as several related but distinct functions.

The ATC surveillance architecture uses two Mode S transponders to communicate aircraft identity, altitude, and other surveillance information. ADS-B extends this capability by automatically broadcasting aircraft-derived data. TCAS independently monitors surrounding transponder-equipped traffic and can issue Traffic Advisories and Resolution Advisories.

Separately, the Cockpit Door Surveillance System provides security-related video surveillance. On the referenced fleet, Airbus documents three video cameras and an LCD display that allow the flight crew to identify persons requesting access to the flight deck.

For pilots and aviation students, the key is to avoid treating all of these functions as one system. Mode S and ADS-B primarily serve ATC surveillance, TCAS provides airborne collision avoidance, and CDSS provides visual monitoring of the cockpit entrance area.

Primary references: Airbus A318/A319/A320/A321 Flight Crew Operating Manual, issue dated 24 November 2025; Airbus A318/A319/A320/A321 Flight Crew Techniques Manual; Airbus A318/A319/A320/A321 Airplane Flight Manual; Airbus A318/A319/A320/A321 Quick Reference Handbook; BH Air Operations Manual Part A.