737 Flight Crew Operations Manual
Warning Systems -
System Description
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15.20.28 D6-27370-866-EGP
Additional symbols are proximate traffic and other traffic. Proximate traffic is
within six miles and 1200 feet vertically, but is not expected to cause a TA or RA
alert. Other traffic is beyond the six mile and 1200 feet vertical criteria. Traffic
symbols are revised as the TCAS system constantly reevaluates the motion of
other airplanes.
If the range of the navigation display does not permit the display of a TA or RA
an OFFSCALE annunciation appears on the navigation display.
TA or RA traffic detected by TCAS which do not provide a bearing generate a no–
bearing text block beneath the TRAFFIC text on the navigation display. The text
block contains distance, altitude, and vertical motion information.
Vertical motion information is indicated by an arrow depicting a climb or descent
if a change of greater than 500 feet per minute is detected.
TCAS display automatically shows when:
• the transponder mode selector is in TA ONLY or TA/RA, and
• a TCAS TA or RA occurs, and
• neither pilot has the TCAS (TFC) display selected, and
• in MAP, center MAP, VOR, or APP modes.
Inhibits
INCREASE DESCENT RAs are inhibited below approximately 1,500 feet radio
altitude.
DESCEND RAs are inhibited below approximately 1,100 feet radio altitude.
RAs are inhibited below approximately 1,000 feet radio altitude. Below 1,000 feet
when the TA/RA mode is selected on the transponder panel, TA only mode is
enabled automatically and the TCAS message TA ONLY displays on the ND.
All TCAS voice annunciations are inhibited below approximately 500 feet radio
altitude.
All TCAS alerts are inhibited by GPWS and windshear warnings.
Mode Control
The TCAS operating mode is controlled from the TCAS/ATC transponder panel.
TCAS is normally operated in the TA/RA mode. However, sometimes it is
necessary to operate in the TA ONLY mode to prevent undesired RAs. For
example, TA ONLY may be selected when intentionally operating near other
airplanes such as might be found in VFR conditions at a busy airport, or on parallel
approach.
September 15, 2016
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