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ATC Transponder - Control and Coordination Data

When you select an ATC transponder, it sends this ATC control panel data to the TCAS computer:

The TCAS mode selection (TA only or TA/RA)

Control of the altitude limits for the TCAS display that shows on the navigation display (ND).

The TCAS computer uses this data from the ATC transponder to calculate the climb or descent to prevent a collision:

24-bit airplane address

Barometric altitude

Maximum true airspeed.

The TCAS computer sends this to the ATC transponder:

General TCAS operational status

Mode S coordination data.


Radio Altimeter Inputs

The TCAS computer gets radio altitude from radio altimeter 1 and 2 transceivers although only one input is necessary for TCAS operation. The data is used by the TCAS computer to calculate some sensitivity levels.

At approximately 1700 feet, the TCAS computer uses radio altitude together with barometric altitude to determine intruders that are on the ground and therefore no threat to the TCAS airplane.

At 1000 feet radio altitude, the TCAs computer inhibits

resolution advisories and TA ONLY will show on the NDs.


TCAS Inputs from ADIRU

The left ADIRU supplies these inputs to the TCAS computer:

Airplane roll attitude

Airplane pitch attitude

Airplane heading.


NOTE: Airplane heading is the only ADIRU input used by the TCAS computer.

NOTE: These inputs are not used by the TCAS computer at this time.

TCAS Outputs to DEUs

The TCAS computer supplies resolution advisory (RA) and traffic advisory (TA) data to the DEUs. This includes all traffic data for TCAS displays.

TCAS Outputs to the FDAU

The FDAU receives the same TCAS data that goes to the DEUs.







The TCAS computer is the main component of the TCAS. It controls these functions:




Air-to-air maneuver coordination.

The TCAS computer sends signals which tell the flight crew to make one of these maneuvers:

Keep the current flight plan

Make flight maneuvers to prevent a possible collision with other airplanes in the area.


Physical Description

The TCAS computer is a 6 MCU size unit. It weighs 28 lbs (11.3 kg).

Functional Description

The TCAS computer transmits 1030 MHz pulse-coded interrogation signals. It receives 1090 MHz pulse-coded reply signals from intruder airplanes with an ATC transponder.

Date: 2016-03-03; view: 1305

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