TCAS - ProFlightOnline

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Introduction
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.
Terminology
•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.
Symbology
•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)
•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.
+10
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
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
• 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.

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