Traffic Alert and Collision Avoidance System

Overview

The Traffic Collision Avoidance System (TCAS) is a system available on aircraft that helps to reduce the risk of airborne collisions. In general commercial airliners operating an IFR flight require TCAS as mandated by various regulatory bodies such as FAA, ICAO, or EASA.

Numerous improvements have been made to this system over the years that enhance the pilot interface and decrease non-optimal pilot handling of advisories from TCAS. The FlyByWire A32NX uses the AP/FD TCAS mode function developed by Airbus.

There are two types of advisories pilots will encounter when TCAS detects an intruder in the flight path of the aircraft.

• Traffic Advisory (TA): Potential threats to monitor
• Resolution Advisory (RA): Collision threats that require intervention

The TCAS panel can be found on the lower pedestal to the right of the throttle quadrant.

Make sure that the ATC system is on AUTO or ON and the ALT RPTG knob is in position ON. The TCAS mode switch should be in position TA/RA when entering the runway for takeoff.

For more information on how to ensure TCAS is active for your flight and the corresponding controls please see the ATC TCAS PANEL page.

Traffic Advisory

This advisory is generated when TCAS detects an intruder along the current flight path it would consider a potential threat. Flight crews will receive multiple cues from TCAS that identifies a TA. No specific action is mandatory during a TA but the flight crew should remain vigilant of intruders and anticipate a potential RA.

• "Traffic, Traffic" aural warning
• Visual amber cues on the navigation display (ND) providing information about the potential threat.
  • See ND Symbology

Once a TA is triggered the AP/FD TCAS will arm itself to notify the crew with the traffic displayed on the ND. The TA will remain active for as long as the threat remains resulting in one of two things:

• Once the predicted flight paths of the aircraft or the aircraft themselves are no longer in proximity, TCAS will issue a "Clear of Conflict"
• If the threat increases, because the aircraft are predicted to approach too close to each other, TCAS will upgrade the Traffic Advisory to a Resolution Advisory.

TA Pilot Actions

As soon as the "Traffic, Traffic" aural warning is heard pilots should begin analyzing the potential threat. Corrective maneuvers should not be performed in response to a TA.

• Confirm the TCAS panel is correctly configured
• Confirm that TCAS is armed in cyan on the PFD's FMA (AP/FD TCAS feature)
  • If TCAS is not armed the flight crew should be mentally prepared to disconnect the autopilot and manually follow TCAS commands
• Ensure A/THR is set to ON
• Pilot monitoring (PM):
  • Check the ND for the potential threat
    • It may be necessary to set the zoom level to 40nm or below
  • Contact ATC about any nearby aircraft
  • Keep pilot flying (PF) informed about the status of the threat
  • Confirm the PF takes the correct actions if the TA upgrades to an RA
  • Consider turning on additional exterior lighting for increased visibility

Resolution Advisory

When a traffic advisory becomes a collision threat an RA is generated. RA actions require the flight crew to promptly follow any commanded actions by TCAS and notify ATC. According to the Airbus Flight Crew Techniques Manual (FCTM) the flight crew must follow TCAS RA commands even in the following situations:

• TCAS RA issues commands that conflict with ATC instructions
• Aural warnings such as "Climb, Climb" or "Increase Climb" exceed max ceiling altitude
• Results in crossing altitude of intruder

AP/FD TCAS shines in this regard allowing for fully automated flight in the case of an RA. Pilots will now have additional information provided to them on the primary flight display (PFD) and navigation display (ND) depending on what actions the flight crew needs to perform to clear the conflict.

• Aural commands instructing the pilot of what type of vertical maneuver to perform
  • See Aural Messages for a list
• Visual red cues on the ND providing information about the potential threat
  • See ND Symbology
• Visual green and red zones on the vertical speed indicators on the PFD
  • See Flight Instrument Indicators

There are generally two types of behaviors associated with an RA - preventative and corrective.

Preventative

This behavior starts with the vertical speed in the green zone of the VSI. It requires the flight crew or commands the autopilot to maintain the current vertical speed and is coupled with an audible alert such as "Monitor V/S". This would help increase the safety margin before any further measures would need to be taken and allow for safe capture of a selected flight level clear of any conflicts.

The following conditions will apply:

• TCAS will maintain a safe V/S target
• Longitudinal modes previously armed will automatically be disarmed except ALT^*
• In the situation that conditions for altitude capture are met a preventative RA will allow for safe capture of the targeted altitude
  • This prevents the aircraft from exceeding a commanded altitude in the FCU
• The audible alert "Adjust V/S" will play and TCAS will avoid conflicts by maintaining a safe vertical speed when attempting to level-off at a targeted altitude
• To ensure a safe speed during any maneuvers A/THR will engage SPEED/MACH

Corrective

This behavior starts with the vertical speed in the red zone of the VSI. As the behavior denotes this RA will require active corrective measure either automatically via the autopilot or manually from the flight crew to fly out of the red zone towards the edge of the green / red zone on the VSI. It is usually coupled with audible alerts such as "Climb, Descend".

The following conditions will apply:

• TCAS will engage and modify vertical guidance to avoid conflict targeting the green zone.
• Targets a V/S of 200ft/min inside the green band on the VSI
• Longitudinal modes previously armed will automatically be disarmed except ALT^*
  • This prevents the aircraft from exceeding a commanded altitude / prevent excursions
  • In this type of RA, a V/S of 0 ft/min is always within the safe zone to prevent commanded altitude excursions allowing for TCAS to reach a targeted flight level if capture conditions are met. Sample scenario:
• To ensure a safe speed during any maneuvers A/THR will engage SPEED/MACH

RA Pilot Actions

As soon as the threat upgrades to an RA, TCAS will engage and provide corrective action based on the types discussed above. While there are many benefits to having AP/FD TCAS installed and having the autopilot perform any corrective maneuvers, the flight crew should still monitor all actions taken by the system and prepare to take manual control at any time.

AP/FD TCAS Actions

• Ensure TCAS is now the active mode on the FMA
• Ensure the AP is targeting the green zone on the VSI
• Notify ATC

Manual TCAS Actions

• Set AP to OFF
• Ensure both FDs set to OFF
• Fly the aircraft into the green zone on the VSI smoothly and promptly
  • TCAS aural commands will also play at this time

Clear of Conflict

TCAS will notify the flight crew via the aural warning "Clear of Conflict" when separation and range from a threat is adequate. At this time the flight crew should perform the following actions:

If maneuver performed using AP/FD TCAS:

• Monitor AP/FD TCAS returns aircraft to previously assigned ATC clearance
• Notify ATC - clear of conflict

If manual actions were taken during the TCAS RA:

• Engage Flight Directors
• Set new commands on the FCU
• Engage the Autopilot
• Notify ATC - clear of conflict

AP/FD TCAS

AP/FD TCAS includes vertical guidance as part of the Auto Flight System (AFS) to support pilots during a TCAS RA. It provides control of the vertical speed via the AFS which is specifically tailored to each target that generated an RA.

Essentially this feature allows the flight crew to resolve TCAS RAs using the autopilot. It is also entirely possible to complete a TCAS RA maneuver manually by using the flight director guidance with the autopilot switched off as well. The major benefit of this system is to provide optimal maneuvers when a conflict arises.

Flight Instrument Indicators

PFD during TCAS RA

As a conflict occurs and the AP/FD TCAS system kicks in typically you will see:

• TCAS in the FMA:
  • TCAS will be armed in cyan below the current vertical guidance mode. (Not Pictured).
  • A mode revision and TCAS will engage with a box around it. (Pictured).
  • TCAS in green after 10s.
• The aircraft will also target a safe vertical speed in the VSI as seen below.

ND Symbology

The following chart explains the various symbols displayed on the navigation display (ND) when TCAS detects potential threats (increasing in severity):

Symbol on ND	Type of Traffic	Information
	Other Traffic	Not a threat. Visible within the surveillance field.
	Proximate Traffic	Not a threat. Identified as a possible intruder within 6 NM and 1200 FT.
	Traffic Advisory (TA)	Possible threat.
	Resolution Advisory (RA)	Collision threat.

This next chart includes additional symbology when traffic is seen on the ND.

Symbol	Information
	This arrow represents traffic that is climbing.
	This arrow represents traffic that is descending.
	Complete picture of traffic on the ND. This example showcases Proximate Traffic that is 1000 ft above the aircraft and is currently climbing.

Aural Messages

The following table includes a list of auditory messages when a TA/RA is detected.

External Resources

Airbus' Safety First publication has great resources further explaining their systems in-depth with supporting graphics and statistics. We've provided a link below to a great article detailing TCAS Alert Prevention (TCAP) and the AP/FD TCAS function.

Safe Handing of TCAS Alerts

Compatibilities and Known Issues

Compatible Networks

Our implementation of TCAS supports the following networks:

• VATSIM
• IVAO
• Live Traffic in MSFS

Known Issues

• Broken support for FSLTL Traffic (sim issue)

  • FSLTL traffic is not visible to TCAS but auditory warnings are still played

  Root Cause for FSLTL + TCAS Issues

  Unfortunately this is an issue with how injected traffic uses certain APIs from MSFS. Asobo seems to be aware of the issue and you can track it on the dev support forum link below:

  AI aircraft generated airborne do not get returned with the GET_AIR_TRAFFIC Coherent call

• No support for offline AI traffic (sim limitation)

• No support of multiplayer (MSFS) traffic (sim limitation)
• Possible false detection of ground traffic
• Possible ghost TA / RA due to jumping traffic (improvements and changes expected)