Tcas - general description General
The TCAS transmits to and receives signals from other airplanes to get altitude, range, and bearing data. The other airplanes report their own altitudes. The range of the other airplanes is calculated by measurement of the time between the transmission of an interrogation and the reception of a response from the other airplanes. Bearing is calculated by the use of directional antennas. TCAS uses these data and inputs from other onboard airplane systems to provide visual indications of the position of other airplanes and to provide visual and aural traffic avoidance alerts.
Tcas - component location General Description
These are the TCAS components:
TCAS directional antennas (2)
TCAS computer
ATC/TCAS control panel.
TCAS interfaces with these other system components:
ATC transponders (2)
Landing gear lever
PSEU
Common display system (CDS) display electronic units
(DEUs) (2)
Remote electronics unit (REU)
Radio altimeters (2)
Ground proximity warning computer (GPWC)
Weather radar
Left air data inertial reference unit (ADIRU)
Suppression coax tees
Flight data acquisition unit (FDAU).
Electronic Equipment Compartment
The TCAS computer is in the electronic equipment
compartment.
Flight Compartment
These are the components in the flight compartment that
interface with TCAS:
Left electronic flight instrument system (EFIS) control panel
Left outboard display unit
Left inboard display unit
Right EFIS control panel
Right outboard display unit
Right inboard display unit
ATC/TCAS control panel.
TCAS - ANTENNA LOCATION
General
The top TCAS directional antenna is at station 385 on top of the fuselage. The bottom TCAS directional antenna is at station 305 on the bottom of the fuselage.
TCAS - POWER, ANTENNAS, ANALOG, DISCRETE INTERFACES AND PROGRAM PINS
General
The TCAS computer has analog and discrete interfaces with these components:
Top and bottom TCAS directional antennas
Landing gear lever switch
Proximity Switch Electronics Unit (PSEU)
Ground proximity warning computer (GPWC)
ILF 404, 405, 410, 414-417, 422-429, 451, 501-509, 510-517, 519,
520-527, 536, 541, 542, 551
Weather radar
DME/ATC/TCAS suppression coax tees
Display electronic unit (DEU) 1 and 2
Remote electronics unit (REU).
Program pins control the configuration of the TCAS computer.
Power
The TCAS computer gets 115v ac from AC transfer bus-1 through the TCAS circuit breaker on the P18 circuit breaker panel.
Antennas
There are two TCAS directional antennas. The TCAS directional antennas receive traffic airplane reply signals. They also transmit the TCAS interrogation signals.
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.
PSEU
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.
TCAS - DIGITAL INTERFACES
General
The TCAS computer has digital interfaces with these
components:
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).
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.