737 Flight Crew Operations Manual
Warning Systems -
System Description
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D6-27370-866-EGP 15.20.27
Callouts are based on radio altitude when the MINS selector is set to RADIO.
Callouts are based on barometric altitude when the MINS selector is set to BARO:
• DH/MDA plus 80 feet – APPROACHING MINIMUMS
• at DH/MDA – MINIMUMS
Traffic Alert and Collision Avoidance System (TCAS)
TCAS alerts the crew to possible conflicting traffic. TCAS interrogates operating
transponders in other airplanes, tracks the other airplanes by analyzing the
transponder replies, and predicts the flight paths and positions. TCAS provides
advisory and traffic displays of the other airplanes to the flight crew. Neither
advisory, guidance, nor traffic display is provided for other airplanes which do not
have operating transponders. TCAS operation is independent of ground–based air
traffic control.
To provide advisories, TCAS identifies a three dimensional airspace around the
airplane where a high likelihood of traffic conflict exists. The dimensions of this
airspace are based upon the closure rate with conflicting traffic.
TCAS equipment interrogates the transponders of other airplanes to determine
their range, bearing, and altitude. A traffic advisory (TA) is generated when the
other airplane is approximately 40 seconds from the point of closest approach. If
the other airplane continues to close, a resolution advisory (RA) is generated when
the other airplane is approximately 25 seconds from the point of closest approach.
The RA provides aural warning and guidance as well as maneuver guidance to
maintain or increase separation from the traffic.
Non–transponder equipped airplanes are invisible to TCAS. RAs can be generated
if the other airplane has a mode C transponder. Coordinated RAs require both
airplanes to have TCAS.
Advisories and Displays
Annunciations associated with TCAS and the traffic displays are discussed further
in Chapter 10.
TAs are indicated by the aural “TRAFFIC, TRAFFIC” which sounds once and is
then reset until the next TA occurs. The TRAFFIC annunciation appears on the
navigation display. The TA symbol appears at the proper range and relative
bearing of the other airplane. Altitude and vertical motion are included with the
symbol if the other airplane is using transponder mode S or C.
RAs are indicated by one or more aural listed in the RA aural table. The TRAFFIC
annunciation and RA symbol which depicts the traffic’s relative bearing, range,
altitude, and vertical motion are on the navigation display similar to the TA
symbol.
September 15, 2016
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