Installation Instructions

GTN 6XX/7XX AML STC Installation Manual 190-01007-A3
Page 2-38 Rev. 4
2.4.14 GMA 35 Wiring Considerations for Failsafe Operation
The GMA 35 includes a failsafe circuit that connects the pilot’s headset and microphone directly to
COM1 in the event that power is interrupted or RS-232 communication with the GTN is lost.
When the GMA 35 is installed with a GTN 750 and a second COM radio, the GTN 750 COM must be
connected to the COM 2 pins (J3501-13,-14,-15) on the GMA 35. The other radio should be connected to
the COM 1 pins. This will prevent the loss of both COM radios if power to the GMA 35 or RS-232
communication to the GMA 35 is lost. The GTN includes a configuration setting to allow the GTN 750
COM radio to appear as COM 1 in the GTN user interface. ‘COM 1 is connected as COM 2’ should be
set to ‘True’ in this case. See Section 5.5.4.8 for information about this setting.
If the GMA 35 is installed with a GTN 725 (no COM) and two other COM radios, wire COM 1 to the
COM 1 pins on the GMA 35, and COM 2 to the COM 2 pins. ‘COM 1 is connected as COM 2’ should be
set to ‘False’ in this case. See Section 5.5.4.8 for information about this setting.
If the GMA 35 is installed with dual GTN 750s, wire GTN 750 #1 to the COM 1 pins on the GMA 35,
and wire GTN 750 #2 to the COM 2 pins on the GMA 35. ‘COM 1 is connected as COM 2’ should be set
to ‘False’ in this case.
2.4.15 Magnetic Compass Recalibration
After reconfiguring the avionics in the cockpit panel, if the GTN unit is mounted less than 12 inches from
the compass, recalibrate the compass and make the necessary changes for noting correction data.
2.4.16 Weather Radar Wiring Considerations
The GTN can interface with weather radar only in a metal aircraft. Any HSDB weather radar wiring in
the radome area must be overbraided. Refer to Section G.1.1 for more information.
Weather radar data can be displayed only on GTN 7XX units. Weather radars that use ARINC 453/708
for data transfer must be connected directly to the GTN 7XX. For an installation that includes a
GWX 68/70 and two GTNs (one of which must be a GTN 7XX), the GWX 68/70 can be connected to any
GTN and the data will be forwarded over HSDB to the GTN 7XX.