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Landing Gear Lever Switch

The discrete from the landing gear lever switch tells the TCAS computer that the landing gear is down. When the TCAS computer gets this discrete, the TCAS computer makes the bottom directional antenna become an omnidirectional antenna.


The discrete from the PSEU supplies in-air or on-ground status to the TCAS computer. The air/ground discrete inhibits TCAS operation on the ground and inhibits tests when in the air. The air/ground discrete also controls flight leg increments in the TCAS nonvolatile memory.

GPWC - Advisory Inhibit Discretes

The GPWC sends one discrete to the TCAS computer. This discrete inhibits TCAS aural and visual warnings when the GPWC makes any voice message.

GPWC - Advisory Inhibit Discretes

The GPWC sends three discretes to the TCAS computer. These discretes inhibit TCAS aural and visual warnings during all GPWS modes except mode 6 (altitude callouts).

Weather Radar

The TCAS computer gets one discrete from the weather radar. This discrete inhibits all TCAS aural warnings and changes RAs to TAs when the weather radar makes a predictive windshear warning.

Suppression Input/Output

The TCAS computer gets a suppression pulse when an ATC transponder or DME interrogator transmits. When the TCAS computer transmits, it sends a suppression pulse to the ATC transponders and the DME interrogators.

DEU - Display Status

A discrete from either DEU goes to the TCAS computer when the DEU loses the ability to show TCAS displays. When the TCAS computer gets this discrete, the TCAS computer does not do these functions:

Send TCAS display outputs to the DEU

Send TCAS aurals to the REU

Transmit coordination data to traffic airplanes with TCAS.


REU - TCAS Aurals - Voice Outputs

The TCAS computer sends resolution advisory (RA) and traffic advisory (TA) aural signals to the remote electronic unit (REU). The REU amplifies the RA and TA aurals. Then it sends them to the flight interphone speakers and headsets to alert the flight crew.

Program Pins

These are the functions for the program pins on the TCAS computer:

Does not show airplanes that are on the ground when own airplane is below 1750 feet AGL

Inhibits self-test in the air

Controls the audio level of the voice outputs

Sets the airplane altitude limit of 48,000 feet so TCAS does not command a climb or increase climb above this altitude.






The TCAS computer has digital interfaces with these


ATC 1 transponder

ATC 2 transponder

Radio altimeter 1 transceiver

Radio altimeter 2 transceiver

Left air data inertial reference unit (ADIRU)

Display electronic unit 2 (DEU 2)

Display electronic unit 1 (DEU 1)

Flight data acquisition unit (FDAU).


Date: 2016-03-03; view: 1169

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Traffic Alert and Collision Avoidance System (TCAS). | ATC Transponder - Control and Coordination Data
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