Boeing 747: TCAS/Transponder Controls

747 TCAS/Transponder Controls by jerome meriweather
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747 Photo and/or Graphic Element
TCAS consists of 2 Mode S Transponders, a TCAS/Transponder control panel, a computer processor, a TCAS EFIS control panel, 2 NDs capable of traffic display, a voice message system, 2 PFDs capable of pitch guidance to avoid transponder-equipped airplanes, and 2 directional antennas (one top and one bottom).

Above / N / Below Switches
Left switch controls Captain's ND and right switch controls First Officer's ND.

Above - Displays altitude reporting traffic from 2700 ft. below to 9900 ft. above your altitude.>
N (Normal) - Displays altitude reporting traffic from 2700 ft. below to 2700 ft. above your altitude.>
Below - Displays altitude reporting traffic from 9900 ft. below to 2700 ft. above your altitude.>

Absolute / Relative Altitude Switches (ABS / REL)
Left switch controls Captain's ND and right switch controls First Officer's ND.

ABS - Target altitude information is displayed as absolute altitude above sea level (3 digits).
REL - Target altitude information is displayed as relative to present altitude ( ± 2 digits) or 00 for co-altitude.

Code Indicator
Indicates code selected with the Code Selectors.

TCAS / XPDR Selector

TEST - Momentarily moving the selector to TEST activates the TCAS system test sequence. The selector is spring loaded to STBY. Holding the selector in TEST allows failed systems to be listed on the ND. TCAS test sequence interrupts the transponder output for a few seconds.
STBY - TCAS and the transponders are in the warm-up cycle.
XPDR - The transponder is ON and TCAS is in the warm-up cycle.
TA - The transponder is ON. TCAS is ON but only the Traffic Advisory function of TCAS is operational. Both Resolution Advisories and pitch guidance are inhibited. The message TA ONLY appears on the ND.
TA/RA - The transponder is ON and all Traffic Advisory and Resolution Advisory function of TCAS are operable.