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Mode Selection Keys
OFF Powers off the GTX 327. 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. The CLR key may be pressed 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 for adjusting contrast and display
brightness.
The GTX 327 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. If the unit detects an
internal failure, the screen displays SELF TEST FAILED.