Cessna 172R Pilot Operating Handbook page 262

2. Mode Selector Knob -- ON.
NOTES
During normal operation with Mode Selector Knob
in ON position, reply indicator flashes, indicating
transponder replies to interrogations.
Mode A reply codes are transmitted in ALT also;
however, Mode C codes are suppressed when the
Mode Selector Knob is positioned to ON.
3, IDT Button -- DEPRESS
momentarily when instructed by
ground controller to "squawk IDENT" ("R" will
illuminate
steadily indicating IDENT operation).
TO TRANSMIT MODE C (ALTITUDE REPORTING) CODES IN
FLIGHT:
Transponder Code Selector Knob -- SELECT assigned code.
Mode Selector Knob -- ALT.
NOTES
When directed by ground controller to
"stop
altitude squawk", turn Mode Selector Knob to ON
for Mode A operation only.
GI Altitude transmitted by the transponder for altitude
squawk and displayed on the KT 76C panel is
pressure altitude (referenced
to
29.92) and
conversion to indicated altitude is done in the
ATC computers.
TO SELF-TEST TRANSPONDER OPERATION:
Mode Selector Knob -- TST Check all displays.
Mode Selector Knob -- SELECT desired function.
S2-8
Dec 2/96
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SECTION 9 - SUPPLEMENTS
CESSNA
SUPPLEMENT 2 - FAA APPROVED
MODEL 172R
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