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Aircraft com munications and navigation systems
which includes two transponders, a control panel and antennas, as described in Chapter 2 1 . Visual warnings can be displayed on the instantaneous vertical speed indicator (IVSI) or electronic flight instrument system (EFIS).
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22.3. 1 Antennas These are located on the top and bottom of the fuselage as illustrated in Figure 22.7; this provides antenna diversity, a technique in which the datalink signal is transmitted along different propagation paths. The upper antenna is directional and is used for tracking targets above the host aircraft; the bottom antenna can either be omnidirectional, or directional as an operator specified option. Interrogation codes are transmitted via the Mode S transponder on a 1 030 MHz carrier wave; reply codes are transmitted on a 1 090 MHz carrier wave. The phase array directional antennas are electronically steerable and transmit in four lateral segments at varying power levels. Note that two Mode S transponder antennas (Figure 22.7) are also required for TCAS operation. The latter is suppressed when the Mode S transponder is transmitting so that TCAS does not track the host aircraft.
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Monitoring of the surveillance airspace volume for aircraft Tracking other aircraft Monitoring its own aircraft altitude Issuing warnings for potential flight path conflicts Providing recommended manoeuvres to avoid potential flight path conflicts.
Inputs to the computer include the host aircraft' s heading, altitude and maximum airspeed. Other configuration inputs include landing gear lever position and weight on wheels sensor.. Collision avoidance algorithms are used to interpret data from the host aircraft and proximate traffic.
22.3.3 Control panel This is a combined ATC/TCAS item, see Figure 22.8. The four-digit aircraft identification code is selected by either rotary switches or push buttons, and displayed in a window. (Refer to Chapter 2 1
22.3.2 Computer This is a combined transmitter, receiver and processor that performs a number of functions including:
Top /lTC antenna
Bottom ATC antenna
Figure 22.7 Location of AT CITCAS antennas
Figure 22.8(a) control panel ·
Location
of ATCITCAS
