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The GTX 330 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 330. 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 In this mode, the transponder replies to interrogations, as
indicated by the Reply Symbol ( ). Replies do not include altitude information.
ALT 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. You may 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 for adjusting contrast and display
brightness.