GTX™ 330/330D
Mode S Transponder
Pilot’s Guide
© Copyright 2002, 2007, 2008
Garmin Ltd. or its subsidiaries
All Rights Reserved
Except as expressly provided herein, no part of this manual may be reproduced, copied,
transmitted, disseminated, downloaded or stored in any storage medium, for any purpose
without the express prior written consent of Garmin. Garmin hereby grants permission to
download a single copy of this manual and of any revision to this manual onto a hard drive or
other electronic storage medium to be viewed and to print one copy of this manual or of any
revision hereto, provided that such electronic or printed copy of this manual or revision must
contain the complete text of this copyright notice and provided further that any unauthorized
commercial distribution of this manual or any revision hereto is strictly prohibited.
This manual is written for software version 6.00 or later, and is not suitable for earlier software
versions. Some differences in operation may be observed when comparing the information in
this manual to earlier or later software versions.
Software License Agreement
Garmin grants you a limited license to use the software embedded in this device (the
“Software”) in binary executable form in the normal operation of the product. Title, ownership
rights and intellectual property rights in and to the Software remain in Garmin.
You acknowledge that the Software is the property of Garmin and is protected under the
United States of America copyright laws and international copyright treaties. You further
acknowledge that the structure, organization and code of the Software are valuable trade
secrets of Garmin and that the Software in source code form remains a valuable trade secret of
Garmin. You agree not to decompile, disassemble, modify, reverse assemble, reverse engineer
or reduce to human readable form the Software or any part thereof or create any derivative
works based on the Software. You agree not to export or re-export the Software to any country
in violation of the export control laws of the United States of America.
CAUTION: The GTX 330 should be turned off before starting or shutting
down aircraft engine(s).
NOTE: Reference to the GTX 330 Transponder throughout this Pilot’s Guide
includes operation of the GTX 330D Diversity Transponder also.
NOTE: Contact a Garmin authorized dealer for software updates.
September 2008
Part Number 190-00207-00 Rev. F
Printed in USA
Limited Warranty
This Garmin product is warranted to be free from defects in materials or workmanship for
two years from the date of purchase. Within this period, Garmin will at its sole option, repair
or replace any components that fail in normal use. Such repairs or replacement will be made
at no charge to the customer for parts or labor, provided that the customer shall be responsible
for any transportation cost. This warranty does not cover failures due to abuse, misuse,
accident or unauthorized alteration or repairs.
Some states do not allow the exclusion of incidental or consequential damages, so the above
limitations may not apply to you.
Garmin retains the exclusive right to repair or replace the unit or software or offer a full
refund of the purchase price at its sole discretion. SUCH REMEDY SHALL BE YOUR SOLE
To obtain warranty service, contact your local Garmin Authorized Service Center. For
assistance in locating a Service Center near you, call Garmin Customer Service at one of the
numbers shown below.
Garmin International, Inc.
Garmin (Europe) Ltd.
1200 East 151st Street
Liberty House, Bulls Copse Road
Olathe, Kansas 66062, U.S.A.
Hounsdown Business Park
Southampton, SO40 9RB, U.K.
NOTE: It is the responsibility of the GTX 330 owner to obtain proper
licensing before using the transponder.
NOTE: The coverage expected from the GTX 330 is limited to line of sight.
Low altitude or aircraft antenna shielding by the aircraft itself may result
in reduced range. Range can be improved by climbing to a higher altitude.
It may be possible to minimize antenna shielding by locating the antenna
where dead spots are only noticed during abnormal flight attitudes.
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  Selects Mode A. In this mode, the transponder replies to
interrogations, as indicated by the Reply Symbol ( ). Replies do not include altitude
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. 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
Keys for Other GTX 330 Functions
IDENT Pressing the IDENT key activates the Special Position
Identification (SPI) Pulse for 18 seconds, identifying your transponder
return from others on the air traffic controller’s screen. The word IDENT
will appear in the upper left corner of the display during this time.
VFR Sets the transponder code to the pre-programmed VFR code selected
during installation configuration (this is set to 1200 at the factory). Pressing
the VFR key again restores the previous identification code. If the VFR Key
is pressed when disabled (dependent upon installation configuration) a VFR
Key Disabled message appears to indicate that no operation took place.
FUNC Changes the page shown on the right side of the display. Display
data includes Pressure Altitude, Flight Time, Altitude Monitor, Count Up,
and Count Down timers. Also displays Outside Air Temperature, Density
Altitude, Contrast, Display, and ADS-B Operation (dependent upon
installation configuration).
START/STOP Starts and stops the Altitude Monitor, Count Up, Count
Down, and Flight timers.
CRSR Initiates starting time entry for the Count Down timer and cancels
transponder code entry.
CLR Resets the Count Up, Count Down, and Flight timers. Cancels the
previous keypress during code selection and Count Down entry. Returns
cursor to the fourth code digit within five seconds after entry.
8 Reduces Contrast and Display Brightness when the respective fields
are displayed (dependent upon installation configuration) and enters the
number eight into the Count Down timer.
9 Increases Contrast and Display Brightness when the respective fields
are displayed (dependent upon installation configuration) and enters the
number nine into the Count Down timer.
Function Display
NOTE: GTX 330 options are normally set at time of installation. For changes
to the GTX 330 parameters, contact your Garmin authorized dealer.
PRESSURE ALT: Displays the altitude data supplied to the GTX 330 in feet,
hundreds of feet (i.e., flight level), or meters (dependent upon installation
FLIGHT TIME: Timer start is configured as either Manual or Automatic.
When Manual, displays the Flight Time, controlled by the START/STOP
and CLR keys. When Automatic, the timer begins when take off is sensed.
ALTITUDE MONITOR: Controlled by START/STOP key. Activates a
voice alarm and warning annunciator when altitude limit is exceeded.
OAT/DALT: Displayed when the GTX 330 is configured with temperature
input. Displays Outside Air Temperature and Density Altitude.
COUNT UP TIMER: Controlled by START/STOP and CLR keys.
keys. The initial Count Down time is entered with the 0 – 9 keys.
CONTRAST: This page is only displayed if manual contrast mode is
selected during installation configuration. Contrast is controlled by the 8
and 9 keys.
DISPLAY: This page is only displayed if manual backlighting mode is selected
during installation configuration. Backlighting is controlled by the 8 and 9
ADS-B: This page is displayed if the ADS-B pilot set option is selected
during installation configuration of an ES enabled GTX 330. ADS-B defaults
to ON at each power cycle. ADS-B ON/OFF is controlled by the START/
STOP key. Turn ADS-B OFF only at the request of ATC.
Altitude Trend Indicator
When the PRESSURE ALT page is displayed, an arrow may be displayed to the right of
the altitude, indicating that the altitude is increasing or decreasing. One of two sizes of arrows
may be displayed depending on the vertical speed rate. The sensitivity of these arrows is
initially set during transponder installation.
Timer Operation
To operate the Flight Timer:
1) Press the FUNC key until FLIGHT TIME is displayed.
2) If the GTX 330 is configured with Automated Airborne Determination, the timer begins
automatically when the unit senses that the aircraft has become airborne. The timer
may be reset to zero at every take off, continue accumulating time at take off, or may be
controlled manually.
3) If desired, press START/STOP to pause or restart the timer.
4) Press CLR to reset the timer to zero.
5) If the timer is configured to start automatically it will stop when the Automated Airborne
Determination senses that the aircraft is on the ground.
To operate the Count Up timer:
1) Press the FUNC key until COUNT UP is displayed.
2) If necessary, press CLR to reset the Count Up timer to zero.
3) Press START/STOP to begin count up.
4) Press START/STOP again to pause the timer.
5) Press CLR to reset the timer to zero.
To operate the Count Down timer:
1) Press the FUNC key until COUNT DOWN is displayed.
2) Press CRSR and use the 0 - 9 keys to set the initial time. All digits must be entered (use
the 0 key to enter leading zeros).
3) Press START/STOP to begin count down.
4) Press START/STOP again to pause the timer.
5) When the Count Down timer expires, the COUNT DOWN banner is replaced with a
flashing EXPIRED, the message “Timer Expired” is heard, and the time begins counting up.
6) Press CLR to reset the timer to the initial time value.
Automatic ALT/GND Mode Switching
If the GTX 330 is configured for Automated Airborne Determination, normal operation
begins when take off is sensed. When the aircraft is on the ground the screen automatically
displays GND. The transponder does not respond to ATCRBS interrogations when GND
is annunciated. When a delay time is set (dependent upon installation configuration), the
GTX 330 waits a specified length of time after landing before changing to GND mode.
Failure Annunciation
If the unit detects an internal failure, the screen displays FAIL. When FAIL is annunciated
no transponder data is transmitted.
Mode S Data Transmission
In addition to 4096 code and pressure altitude, the GTX 330 is capable of transmitting
aircraft identification, transponder capability, and maximum speed range. Aircraft
identification is commonly referred to as FLT ID (Flight Identification). The GTX 330 may be
configured by the installer to allow the flight crew to enter FLT ID for each flight. An example
is when air-carrier service requires changing the FLT ID.
The FLT ID may consist of the aircraft registration or a flight number as agreed upon with
the local aviation authority. In either case, the FLT ID must be the same aircraft identification
that appears in the flight plan to correlate the aircraft identification seen on ATC radar with the
correct voice call sign for the aircraft. If no flight plan is filed with the aviation authority (as
may be permitted by regulations), the FLT ID entered is the aircraft registration marking.
When flight crew entry of the FLT ID is not required, the installer configures the
system to report the aircraft identification according to local aviation requirements. In this
configuration, alteration of the FLT ID by the flight crew is not possible.
Altitude Monitor Operation
To operate the Altitude Monitor:
1) Climb to assigned altitude.
2) Press the FUNC key until ALT MONITOR is displayed.
3) Press START/STOP key to start monitoring altitude.
4) Press START/STOP key again to cancel Altitude Monitor.
Altitude deviation is shown in hundreds of feet ABOVE or BELOW the selected altitude.
When the aircraft’s altitude exceeds the deviation limit, ABOVE or BELOW flashes and an
audio tone or the message “Leaving Altitude” is heard. ABOVE or BELOW flashes until the
aircraft returns to within 100’ of the selected altitude.
To select a new monitored altitude, press the START/STOP key to deactivate, then press
again to activate the new monitored altitude.
If another function is selected for viewing, such as a Timer or Pressure Altitude, the
Altitude Monitor is automatically displayed with a flashing alert when the altitude excursion
exceeds the configured deviation value. The Altitude Monitor stops when the current
deviation exceeds 1000 feet plus the configured deviation value.
The maximum configured deviation values that can be set by a Garmin authorized service
center are as follows:
Flight Level or Feet Maximum Limits – 300 feet BELOW, 0 feet to 1999 feet ABOVE
Meters Maximum Limits – 300 meters BELOW, 0 meters to 609 meters ABOVE
Entering a Flight ID Number
When configured for FLT ID PWR-UP ENTRY at installation, the flight crew must enter
the Flight ID before the GTX 330 will operate. After the flight crew enters the correct Flight
ID, the aircraft identification that is transmitted in response to ATC radar interrogations is
properly correlated with the associated call sign for voice communication with the aircraft.
If the FLT ID PWR-UP ENTRY is required but does not appear at power up, contact a
Garmin authorized service center for GTX 330 configuration.
No space is needed when entering Flight ID characters. When a Flight ID contains a
space, the GTX 330 automatically removes the spaces upon completion of Flight ID entry.
At system power-up the FLT ID may
appear with no number (as shown) or with the
last FLT ID entered. The cursor covers the
entire FLT ID field.
If the Flight ID appearing at turn-on is
correct, press the CRSR key to move the cursor
to the OK? field. Press CRSR again to accept
the FLT ID. The transponder then begins
normal operation.
When no FLT ID appears or the FLT
ID must be changed, press the number keys
corresponding to the alphanumeric character
entry. For example, to enter the letter R press
the 5 key four times.
Each time an alphanumeric character is entered, press the CRSR key to move the cursor
to the next blank field. Pressing the CLR key moves the cursor back to the previous character.
After the complete FLT ID is entered, press the CRSR key to move the cursor to the OK? field.
Press CRSR again to accept the FLT ID.
When FLT ID entry is complete the transponder begins normal operation.
If an error is made while entering a FLT ID, press the CLR key to back up to any point,
including highlighting the OK? field. If an incorrect FLT ID is discovered after the unit begins
operation, turn the GTX 330 off. Then turn it back on and reenter the correct FLT ID.
GTX 330 Mode S Transponder Features
GTX 330D Diversity Mode S Transponder
The GTX 330D Diversity Mode S Transponder incorporates antennas mounted on the
top and bottom of the aircraft for dependable operation while maneuvering. Top and
bottom antennas are less prone to antenna shadowing by the aircraft structure while turning.
A top mounted antenna is in a better viewing position for interrogation and reply to overhead
Traffic Information Service
The GTX 330 Mode S transponder provides a data link for Traffic Information Service
(TIS). TIS is derived through a Mode S transponder data link and viewed on a multifunction
display. ATC radar sends a traffic picture within a radius of 55 miles from select sites. The
TIS protected area is a cylinder of 7-mile radius, extending 3500’ above and 3000’ below the
aircraft. Refer to the AIM Chapter 1 for more details.
TIS provides a graphic display of traffic information in the cockpit for non-TCAS equipped
aircraft. Transponder-equipped aircraft can be displayed within the coverage volume within
range of your position on indicators such as a Garmin GNS 430 or GNS 530, GNS 480, and
GMX 200. Aircraft without an operating transponder are invisible to TIS. Refer to 400/500
series, GNS 480, or GMX 200 pilot literature for details.
GTX 330 ES Options
Automatic Dependent Surveillance-Broadcast (ADS-B) technology improves situational
awareness and flight safety. With ADS-B capabilities, position, velocity, and heading
information are automatically transmitted to other aircraft and ground stations. The current
air traffic control system depends on a transponder request for pertinent aircraft information
and does not include 3D position. ADS-B provides automatic transmission of aircraft
information without a request.
Audio Alerts
(Setting options; male/female voice or tone, and volume level.)
• “Leaving Altitude” - Altitude Monitor deviation is exceeded.
• “Traffic” - TIS traffic alert is received.
• “Traffic Not Available” - TIS service is not available or out of range.
• “Timer Expired” - Count down time has expired.
© 2002, 2007, 2008 Garmin Ltd. or its subsidiaries
Garmin International, Inc.
1200 East 151st Street, Olathe, Kansas 66062, U.S.A.
Garmin (Europe) Ltd.
Liberty House, Bulls Copse Road, Hounsdown Business Park,
Southampton, SO40 9RB, U.K.
Garmin Corporation
No. 68, Jangshu 2nd Road, Shijr, Taipei County, Taiwan
Part Number 190-00207-00 Rev. F
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