Garmin GTXTM 327 TRANSPONDER INSTALLATION MANUAL
Brand: Garmin, Pages: 55
Page 26 from 55
Page 18 GTX 327 Installation Manual
This page intentionally left blank
Page 27 from 55
GTX 327 Installation Manual Page 19
3. POST INSTALLATION CONFIGURATION & CHECKOUT PROCEDURE
3.1 AIRCRAFT STATION LICENSING REQUIREMENTS
The Telecommunications Act of 1996, effective February 8, 1996, provides the FCC discretion to
eliminate radio station license requirements for aircraft and ships. The GTX 327 installation must comply
with current transmitter licensing requirements. To find out the specific details on whether a particular
installation is exempt from licensing, please see FCC Fact Sheet PR 5000 or contact the FCC by phone at
If an aircraft license is required, make application for a license on FCC form 404, Application for Aircraft
Radio Station License. The FCC also has a fax-on-demand service to provide forms by fax at
The GTX 327 owner accepts all responsibility for obtaining the proper licensing before using the
The coverage you can expect from the GTX 327 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.
Figure 3-1. GTX 327 Front Panel
The GTX 327 should be turned off before starting aircraft engine(s).
If the GTX 327 is configured with Automated Airborne Determination, flight
operation is automatic and not dependent on user mode selection. Whether STBY,
ON or ALT is selected on the ground, the transponder annunciation continues to
indicate STBY and does not respond to radar or TCAS interrogations. When liftoff
is sensed, the unit automatically selects the ALT mode.
Page 28 from 55
Page 20 GTX 327 Installation Manual
3.2.1 Function Selection Switches
The function selection switches are:
• OFF Powers off the GTX 327. Pressing the 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
• ON Selects Mode A. In this mode, the transponder replies to Mode A and Mode C
interrogations, as indicated by the Reply Symbol (“
®”), but the replies do not
include altitude information.
• ALT Selects Mode A and Mode C. In ALT mode, the transponder replies to
identification and altitude as indicated by the Reply Symbol (“
®”). Replies to
altitude interrogations include the standard pressure altitude (29.92 inches Hg.)
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 switch is in the ON or ALT position the transponder
becomes an active part of the Air Traffic Control Radar Beacon System
(ATCRBS). The transponder also responds to interrogations from TCAS
• IDENT Pressing the IDENT key activates the Special Position Identification (SPI) Pulse
for 18 seconds, identifying the transponder return from others on an air traffic
controller’s screen. During the IDENT period, the word ‘IDENT’ appears in the
upper left corner of the display.
• VFR Sets the transponder code to the pre-programmed VFR code selected in
Configuration Mode (set to 1200 at the factory). Pressing the VFR key again will
restore the previous identification code.
Page 29 from 55
GTX 327 Installation Manual Page 21
• FUNC Changes the page shown on the right side of the display. Display data
includes Pressure Altitude, Flight Time, Count Up and Count Down timers.
In the Configuration Mode, steps through the function pages.
Pressure Alt: Displays the altitude data supplied to the GTX 327 in feet,
flight level format or meters, depending on configuration
Flight Time: Displays the Flight Time which is controlled as configured on
Configuration #1 page.
Count Up Timer: Controlled by START/STOP and CLR buttons.
Count Down Timer: Controlled by START/STOP, CLR, and CRSR buttons.
Count down time entered with 0 – 9 buttons.
Contrast: Controlled by 8 and 9 buttons.
Display Brightness: Controlled by 8 and 9 buttons
•START/ STOP Starts and stops the Count Up, Count Down and Flight Time. In the
Configuration Mode, reverses through the function pages.
•CRSR Activates the change fields for the Count Down timer.
•CLR Resets the Count Up, Count Down and Flight timers. Returns cursor to
fourth code digit up to five seconds after code entry is complete.
•8 Reduces screen Contrast and Display Brightness. Enters the number eight
into the Count Down timer.
•9 Increases screen Contrast and Display Brightness. Enters the number nine
into the Count Down timer.
Page 30 from 55
Page 22 GTX 327 Installation Manual
3.2.2 Function Display
PRESSURE ALT Displays the altitude data supplied to the GTX 327 in feet, hundreds of
feet (i.e., flight level), or meters, depending on configuration.
FLIGHT TIME Displays the Flight Time, controlled by the START/STOP key or by one
of four airborne sources (squat switch, GPS ground speed recognition,
airdata airspeed recognition or altitude increase) as configured during
installation. The timer begins when the GTX 327 determines that the
aircraft is airborne.
COUNT UP TIMER Controlled by START/STOP and CLR keys.
COUNT DOWN TIMER Controlled by START/STOP, CLR, and CRSR 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 in
Configuration Mode. Contrast is controlled by the 8 and 9 keys .
DISPLAY This page is only displayed if manual backlighting mode is selected in
Configuration Mode. Backlighting is controlled by the 8 and 9 keys.