A320’s Traffic Alert and Collision Avoidance System (TCAS)!

A320 - AviatorsBuzz

The Traffic Alert and Collision Avoidance System (TCAS) uses the transponder signals received from other aircraft to determine range, bearing, altitude, and closure rate.

TCAS detects any transponder equipped aircraft flying in its vicinity.

The detection capability is limited to intruders within a range of 30-40 NM and within 9900’ of the aircraft.

Potential collision threats are displayed on the Navigation Display.

If necessary, aural vertical orders are issued to avoid a collision.

AREA OF SCANNING FOR TRAFFIC BY TCAS - AviatorsBuzz
(Source: BOND AVIATION MANUAL)

TCAS traffic is categorized into one of four types based on the collision threat.

The four types of traffic are:

  • Other – The intruder aircraft is displayed but does not pose a collision threat.
  • Proximate – The intruder aircraft does not currently pose a collision threat but is within 6 NM and 1200’.
  • Traffic Advisory (TA) – The intruder aircraft does not pose an immediate collision threat but is in close proximity to the aircraft.  
  • Resolution Advisory (RA) – The intruder aircraft poses an immediate collision threat.  Aural warnings commanding vertical evasive maneuvers to avoid collision are annunciated (e.g., “CLIMB, CLIMB”). 

TAU FOR TRAFFIC ADVISORY AND RESOLUTION ADVISORY

TAU FOR TRAFFIC ADVISORY AND RESOLUTION ADVISORY - AviatorsBuzz
(Source: BOND AVIATION MANUAL)

COCKPIT EQUIPMENTS INVOLVED FOR TCAS OPS

COCKPIT EQUIPMENTS INVOLVED FOR TCAS OPS - AviatorsBuzz
(Source: AIRBUS TECH MANUAL B1)

TCAS traffic displayed on the NDs includes the relative altitude of the traffic and its vertical trend, if greater than 500 feet per minute.

If no relative altitude is displayed, the traffic is at your altitude or no altitude is being reported. 

The location of the traffic on the NDs indicates its relative position.

The shape and color indicates the type of traffic and level of threat.

Traffic may be partially displayed when its range is beyond the selected ND range. 

SYMBOLS OF TRAFFIC/TA/RA ON ND

SYMBOLS OF TRAFFIC/TA/RA ON ND - AviatorsBuzz
(Source: AIRBUS TECH MANUAL B1)

If TCAS cannot determine the bearing of a TA or RA intruder, the distance, relative altitude, and vertical trend of the intruder are displayed at the bottom of the ND in amber or red as appropriate.

If only the distance of a TA or RA intruder can be determined, it is displayed at the bottom of the ND in amber or red as appropriate.

If a TA is generated, an aural “TRAFFIC, TRAFFIC” warning is annunciated and the intruder is displayed on the NDs as a solid amber circle if a range of 40 NM or less is selected.

RAs are displayed as red squares on the ND.

Two types of RAs are provided:

  • Corrective RA – A change in vertical speed is required to ensure safe separation.
  • Preventative RA – No change in vertical speed is required to ensure safe separation.

If a corrective RA is generated:

  • An aural warning directing the appropriate pilot action is annunciated (e.g., “CLIMB, CLIMB, CLIMB”).
  • The intruder is displayed on the NDs as a solid red square if a range of 40 NM or less is selected.
  • The vertical speed range where the risk of collision is high is displayed in red on the PFDs.
  • The recommended vertical speed range is displayed in green on the PFDs. 
  • The grey backgrounds on the heading and airspeed scales are removed.

CORRECTIVE RA/PREVENTIVE RA

CORRECTIVE RA/PREVENTIVE RA- AviatorsBuzz
(Source: AIRBUS TECH MANUAL B1)

If a preventative RA is generated:

  • A “MONITOR VERTICAL SPEED” aural warning is annunciated.
  • The intruder is displayed on the NDs as a solid red square if a range of 40 NM or less is selected.
  • The vertical speed range where the risk of collision is high is displayed in red on the PFDs (no specific recommended vertical speed range is displayed).
  • The grey backgrounds on the heading and airspeed scales are removed.

 

RESOLUTION ADVISORY DEFINITION
CLIMB, CLIMB, CLIMB A climb is required to maintain safe separation.
CLIMB, CROSSING CLIMB A climb is required to maintain safe separation & the aircraft will pass through the intruder’s altitude.
INCREASE CLIMB Annunciated after the CLIMB message if vertical speed is not sufficient to achieve safe separation.
DESCEND, DESCEND NOW Annunciated after the CLIMB message if the intruder’s flight path has changed.
DESCEND, DESCEND, DESCEND A descent is required to maintain safe separation.
DESCEND, CROSSING DESCEND A descent is required to maintain safe separation & the aircraft will pass through the intruder’s altitude.
INCREASE DESCENT Annunciated after the DESCEND message if vertical speed is not sufficient to maintain safe separation.
CLIMB, CLIMB NOW Annunciated after the DESCEND message if the intruder’s flight path has changed.
ADJUST VERTICAL SPEED A reduction in climb or descent rate is required to maintain safe separation.
MAINTAIN VERTICAL SPEED Maintain the vertical speed indicated on the PFD.
MONITOR VERTICAL SPEED Preventative RA. Annunciated to direct the crew to monitor the vertical speed.
MAINTAIN VERTICAL SPEED, CROSSING MAINTAIN Maintain the vertical speed indicated on the PFD & the intruder will pass through the aircraft’s altitude.
CLEAR OF CONFLICT Annunciated after an RA if distance from the intruder is increasing and separation is sufficient.

The following TCAS displays and aural warnings are inhibited based on radio altitude:

  • The display of intruders flying below 380’ AGL is inhibited when the aircraft is below 1700’ AGL.
  • All “INCREASE DESCENT” RAs are inhibited below 1450’ AGL.
  • All “DESCEND” RAs are inhibited below 1000’ AGL.
  • All RAs below 900’ AGL are converted to TAs.
  • All RAs and TAs are inhibited below 400’ AGL.

When RAs are inhibited or TA ONLY is selected on the ATC/TCAS panel, a white TA ONLY message is displayed on the NDs.

INHIBITION CONDITIONS OF TCAS BASED ON RA

INHIBITION CONDITIONS OF TCAS BASED ON RA - AviatorsBuzz
(Source: AIRBUS TECH MANUAL B1)
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Ria & Kartik
Follow our TechTalks with Ria Maini and Kartik Bhatnagar, both commercial pilots, rated and endorsed on the A320. Although they recently stepped into their aviation career, nothing has stopped them from taking their knowledge to the next level, with successful experience in coaching on the subject of A320’s for aspiring pilots and a memory refresh for the experienced ones. Curiosity, passion for flying and avionics led them to start "A320 Trivia", and their endeavour has been to share their knowledge to benefit all aviation enthusiasts and pilots, and to highlight key dynamics of the versatile aircraft. You are welcome to share your valuable inputs and further enable this page, to be an expert guide/reference, polestar for all to follow. If you are interested in discovering new and mind boggling facts on the aircraft & technical general, catch up on our weekly blog!