Garmin G5 Electronic Flight Instrument Part 23 AML STC Installation Manual
190-01112-10
Rev. 21
Page 99
material between the face sheets is not conductive and therefore care must be taken to make sure proper
bonding of the equipment has taken place. The top and bottom faces sheets must be grounded to each
other and one of the face sheets must be grounded to the airframe.
The instrument panel must be of metal construction so that remotely mounted units have a metal ground
reference back to the other G5 interfacing equipment mounted on the instrument panel. For metal
aircraft the latter is achieved inherently through the metallic aircraft structure. For composite aircraft a
ground plane (or reference) may need to be created to achieve a comparable ground. This procedure is
described in Section 4.5.2.
Electrical equipment, connectors with shields connected to backshell, and supporting brackets
shall be electrically bonded. The electrical bond shall achieve a direct current (DC) resistance of 2.5 mΩ
or less between faying surface, shelves, and the aircraft structure. Compliance shall be verified by
inspection.
4.5.1
Metal Aircraft
The GAD 29/29B and GAD 13 support brackets require a resistance value of 2.5 milliohms or less
between individual mating surfaces. For general steps on how to prepare aluminum surfaces for
electrical bonding refer to Section 4.5.3.
If the instrument panel is attached by vibration mounts, verify that the mounts are grounded to the
metallic airframe structure by means of a bonding jumper. Ensure that the installed bonding jumper
meets the following specifications.
1.
The braid is a 7/16" or wider tubular braid (part number QQB575R30T437, 24,120 circular mils)
or a 3/4" or wider flat braid (part number QQB575F36T781, 20,800 circular mils).
2.
The braid contains a terminal lug (mil-spec MS20659-130) at each end.
3.
The strap length is as short as possible, not exceeding 6 inches.
Ensure that each terminal lug is secured to its respective mating surface with one #10 steel bolt and one
flat washer (part number AN970-3). Lugs and washers should be center-aligned and flush on all outside
edges. These components should be in full contact with the mating surface.
4.5.2
Nonmetallic Aircraft
NOTE
Carbon reinforced composite (with or without mesh) or fiberglass with mesh is considered to be
conductive. Wood, Kevlar and fiberglass without mesh is considered to be non-conductive.
If the equipment is mounted in the metallic instrument panel then the bonding should be accomplished
like that for metal aircraft (Section 4.5.1). For composite areas of the aircraft the GAD 29/29B and GAD
13 must be electrically bonded to the metallic instrument panel either directly through the unit remote
install/mounting rack or with heavy-duty dead soft aluminum tape such as 3M Heavy Duty Aluminum
Foil Tape 438. The following guidance should be used for locating and bonding the LRU:
1.
Identify a location for the LRU which is close to the instrument panel or the grounding structure
for the instrument panel.
2.
Identify a route between the LRU location and the instrument panel ground that will
accommodate a strip of aluminum tape with a width of at least four inches and a length-to-width
ratio of 7:1.
