AIRPLANE
OPERATIONS
MANUAL
NAVIGATION AND
COMMUNICATION
MARCH 30, 2001
2-18-22
Page
1
Code
02
THIRD VHF NAVIGATION/COMMUNICATIONS
SYSTEM
The airplane may be equipped with a third VHF
Navigation/Communications System.
The third Navigation receiver is required to perform CAT-IIIa
operations. It feeds the HGS with high reliability ILS data, which are
compared with those received from Navigation receiver #1. In case of
a miscomparison between both signals, the HGS will not be able to
engage CAT-IIIa mode.
All functions of the Collins VIR-433 System are controlled by the
CTL-23C VHF Control Panel located at the main panel.
The Avionics Master DC Bus 1 supplies the third VHF
Navigation/Communications System with a protective 5A circuit
breaker.
THIRD VHF NAV/COM CONTROLS AND INDICATORS
1 - COM/NAV SWITCH
− This is a 2-position, spring-loaded toggle switch.
− In the UP position, the Frequency Select Knob will affect the
COM display.
− In the DOWN position, the Frequency Select Knob will affect the
NAV display.
2 - FREQUENCY SELECT KNOBS
− Two concentric knobs control the COM or NAV frequency
displays.
− The large knob changes the three digits to the left of the decimal
point in 1 MHz steps.
− The smaller knob changes the two digits to the right of the
decimal point.
− Numbers roll over at the upper and lower frequency limits.
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