190-02081-03
GFC 600H HFCS Part 27 STC Maintenance Manual
Rev. 3
Page 4-8
4.5 Electrical Bonding Check
Electrical equipment, supporting brackets, and racks must be electrically bonded to the rotorcraft's main
structure.
During the check, any cables normally attached to the LRU must be disconnected from the LRU.
Resistance must be measured from a bare metal portion of the LRU to an airframe grounding location. The
airframe grounding location is identified in Table 4-2.
Table 4-2 Existing Electrical Bonding Requirement (Milliohm)
If the measured resistance is greater than applicable values in Table 4-2, electrical bonding must be
repaired and meet applicable requirements defined in Table 4-3. Electrical bonding of metallic parts must
be accomplished with Type No. 1 procedure detailed in Section 20-02-07 of the
Airbus Helicopters
Standard Procedures Manual
(MTC) and using materials specified in Section 20-01-01. Overseal bond
areas per 20-02-07. Refer to P/N 190-02081-01 for more details.
Table 4-3 Repaired Electrical Bonding Requirement (Milliohm)
4.6 Magnetic Field Updates
The GMC 605H internal AHRS unit and GSU 75H AHRS utilizes an Earth magnetic field model. This
model is updated once every five years by the owner/operator as part of the Aviation Database
maintenance. A service bulletin containing the updated magnetic field model and instructions for
installation can be obtained from the dealer resource center or by contacting Garmin.
LRU
Maintenance Requirement
Resistance [mΩ]
Where to Make Measurement
GMC 605H
10.0
GMC to Instrument Panel
GFS 83
GSU 75H
GRS 79H
5.0
LRU chassis to keel beam. For AHRS, do not use
the shelf.
GMU 44( )
5.0
GMU to stringer or keel. Not to the GMU bracket.
GTP 59
5.0
GTP tip to center keel.
LRU
Repaired Requirement
Resistance [mΩ]
GMC 605H
5.0
GFS 83, GSU 75H
OR
GRS 79H, GMU 44( ), GTP 59
2.5