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The GTX 328 transponder is powered on by pressing the STBY, ALT or ON keys, or by a remote avionics master
switch (if applicable). After power on, a start-up page is displayed while the unit performs a self test.
Mode Selection Keys
OFF Powers off the GTX 328. Pressing STBY, ON or ALT
Key powers on the transponder displaying the last active
identification code.
STBY Selects the standby mode. When in standby mode,
the transponder will not reply to any interrogations.
ON Selects Mode A. In this mode, the transponder replies to interrogations,
as indicated by the Reply Symbol ( ). Replies do not include altitude information.
ALT
Selects Mode A and Mode C. In ALT mode, the transponder replies to
identification and altitude interrogations as indicated by the Reply Symbol ( ). Replies
to altitude interrogations include the standard pressure altitude received from an external
altitude source, which is not adjusted for barometric pressure. The ALT mode may be
selected in aircraft not equipped with an optional altitude encoder; however, the reply
signal will not include altitude information.
Any time the function ON or ALT is selected the transponder becomes an active part of
the Air Traffic Control Radar Beacon System (ATCRBS). The transponder also responds to
interrogations from TCAS equipped aircraft.
Code Selection
Code selection is done with eight keys (0 – 7) providing 4,096 active identification codes.
Pushing one of these keys begins the code selection sequence. Digits that are not yet entered
appear as dashes. The new code is activated when the fourth digit is entered. Pressing the CLR
Key moves the cursor back to the previous digit. Pressing the CLR Key when the cursor is on
the first digit of the code, or pressing the CRSR Key during code entry, removes the cursor and
cancels data entry, restoring the previous code. Press the CLR Key up to five seconds after code
entry is complete to return the cursor to the fourth digit. The numbers 8 and 9 are not used for
code entry, only for entering a Count Down time, and contrast and display brightness.