User Guide

Series III Avionics
Pilot's Guide
Page 22
CODE SELECT Knobs - The outer knob selects the
left two digits of the transponder code. the inner
knob selects the right two digits.
The range for each knob is 00 through 77.
When the FUNCTION SELECTOR is in VFR
position, the CODE SELECT knobs are disabled
because the VFR code (1200 in the U.S.A.) is
automatically selected.
IDENT
Pushbutton - During normal operation, this
pushbutton is pressed and released only when ATC
requests "squawk ident". The identification mode
will then remain active for 15 to 30 seconds,
causing the transponder to transmit a special
identification code each time it is interrogated by
ATC radar. The ID annunciation will appear on the
display each time an interrogation occurs. After
this, the TRS-42A will revert to its selected mode
(ON, ALT, or VFR).
TRANSPONDER SYSTEM 1 or 2 SELECT
Pushbutton - Selects either System 1 or System 2
when more than one transponder system is
installed. The selected system number is displayed
below the letters ACT on the display. If only one
system is installed, the number 1 is always
displayed.