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Presentation Transcript

The Traffic Alert and Collision Avoidance System (TCAS) is an airborne system that interrogates transponders in other aircraft. From the replies received, the system analyzes the intruding aircraft’s altitude (if altitude reporting), closure rate, and projected flight path to predict a penetration of the airspace about your aircraft. The system then displays the other aircraft visually and aurally to alert you to any potential threats of airspace conflict. The system can report a resolution advisory (RA) only if the other transponder is transmitting an altitude.


  • Closest Point of Approach (CPA): The predicted point in space at which the intruder will be closest to your aircraft.

  • Display Volume*: The maximum area displayed on the PFDs/MFD selected by the range and the Above and Below selections.

    • Above (ABV): In this setting the display shows 9,900’ above and 2,700’ below the aircraft altitude. Used during takeoff and climbs.

    • Below (BLW): The display shows 9,900’ below and 2,700’ above the aircraft altitude. Used during descents and landing.

    • Normal (no representation): The display shows 2,700’ above and below the aircraft altitude. Used during cruise.

Terminology continued

  • Above/ Below (Selectable on CDU for ATC1 transponder): In this setting the display shows 9,900’ above and 9900’ below the aircraft altitude.


  • Other Traffic: Represented by an open diamond. OT is intruder traffic that does not yet pose a threat and has a relative altitude > 1200ft or a range > 6NM from your aircraft.

  • Proximate Traffic: Indicated by a solid diamond. PT is also intruder traffic that does not yet pose a threat and has a relative altitude > 1200ft or a range > 6NM from your aircraft.

Symbology continued
Symbology (continued)

  • Relative altitude is indicated by a plus or minus sign and two digits in hundreds. “+10” means the aircraft is 1,000 feet above yours. Arrows () indicate at least 500 FPM rate of climb or descent and direction.

  • Traffic Advisory (TA): Indicated by a solid yellow circle and representing a potential threat that may become RA traffic. Coupled with an aural announcement of “TRAFFIC, TRAFFIC”. Threat is 20 to 48 seconds prior to CPA.


Symbology (continued)

  • Resolution Advisory (RA): Depicted as a red square. RA traffic is traffic that the TCAS computer has determined to be a potential threat and requires immediate pilot action. Accompanied by an aural message such as “CLIMB, CLIMB”, the Threat is 15 to 35 seconds from CPA.

Concept of operation
Concept of Operation

TCAS creates a “bubble” of protected airspace around your airplane. At approx 50 NM out TCAS begins to “track” other transponder equipped aircraft. At approx 40 NM out other transponder equipped aircraft can be displayed on the active PFD/MFD. At 30 approx NM a data-link is established with other Mode S transponders to begin conflict resolution planning. At 20 to 48 seconds prior to CPA a TA is issued. AT 15 to 35 seconds from CPA an RA is generated. If the RA is ignored, the crew response is too slow, or the conflict traffic alters its course a corrective RA is issued. When the traffic is no longer a threat TCAS announces “CLEAR OF CONFLICT”.

General guidlines
General Guidlines

  • Crews are authorized to deviate from an ATC clearance and will do so in order to correctly respond to a Resolution Advisory (RA). The TCAS is the primary means of collision avoidance.

  • The correct terminology to use when reporting deviation from an altitude assignment in order to respond to a RA is either “TCAS climb” or “TCAS descent.”

  • When operating IMC, all crews must respond to an RA.

  • When operating VMC, all crews will respond to an RA unless the threat traffic is identified.