Mounting Considerations; Cabling And Wiring Considerations; Air Circulation And Cooling; Compass Safe Distance - Garmin GTN 725 Installation Manual

2.5

Mounting Considerations

The GTN is designed to mount in the avionics stack in the aircraft instrument panel within view and reach
of the pilot. The primary unit location should minimize pilot head movement when transitioning between
looking outside of the cockpit and viewing/operating the GTN. The location should be such that the GTN
unit is not blocked by the glare shield on top, or by the throttles, control yoke, etc. on the bottom. If
aircraft has a throw-over yoke, be sure the yoke does not interfere with the GTN.
2.6

Cabling and Wiring Considerations

Wiring should be installed in accordance with AC 43.13-1B Chapter 11. For dual GTN unit installations,
care should be taken to ensure separation between wires of redundant systems to reduce the possibility of
loss of navigation due to a single event. When wire separation cannot be achieved, the following issues
should be addressed:
It should not be possible for a cable harness to be exposed to wire chafing in a manner that both
GPS units fail simultaneously;
The cable harness should not be located near flight control cables and controls, high electrical
capacity lines or fuel lines;
The cable harness should be located in a protected area of the aircraft (e.g., isolated from engine
rotor burst); and
Do not route cable near high-energy sources.
Wiring which is required to be shielded must be shielded per Section 2.6. Pigtail lengths
must be less than 3.0 inches.
Refer to Section 3.7 and Section 3.8 for connector and tooling information.
Refer to Section 3.10 for recommended coax cable.
Refer to Appendix D for the appropriate wiring connections to assemble the wiring connector.
Once the cable assemblies have been made, attach the cable connectors to the rear connector plate. After
installing the mounting tube, attach the assembled connector plate. Route the wiring bundle as
appropriate. Use 22 to 24 AWG wire for all connections except for power. Use 20 AWG for power and
ground. Avoid sharp bends.
2.7

Air Circulation and Cooling

The GTN unit meets all TSO requirements without external cooling. However, as with all electronic
equipment, lower operating temperatures extend equipment life. On the average, reducing the operating
temperature by 15° to 20°C (27° to 36°F) reduces the mean time between failures (MTBF).
Units tightly packed in the avionics stack heat each other through radiation, convection, and sometimes
by direct conduction. Even a single unit operates at a much higher temperature in still air than in moving
air. Fans or some other means of moving the air around electronic equipment are usually a worthwhile
investment.
The GTN has a cooling fan integrated into the backplate to draw forced-air cooling through the unit.
There are inlets along the left, right, and bottom sides of the GTN bezel that allow air to flow through the
unit. Ensure that there are no obstructions to the air inlets. Air should be able to freely flow from the bezel
inlets to the backplate fan outlet on the rear of the unit.
2.8

Compass Safe Distance

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.
GTN 725/750 TSO Installation Manual
190-01007-02
NOTE
Page 2-11
Rev. A