Electrical Bonding Test; Table 4-3 - Lightning Strike Inspection Procedure - Garmin GFC 500 Maintenance Manual

Table 4-3 – Lightning Strike Inspection Procedure
Item Description/Procedure
In the event of a suspected or actual lightning strike to the aircraft, the bonding
components for the GFC 500 Autopilot (bonding straps, mounting hardware etc.) must be
inspected. If any damage is found, damaged components must be replaced in accordance
GMC 507, GSA 28
with specifications and procedures shown in Section 6. If any bonding components are
replaced, measure the resistance between the replaced component and aircraft ground.
Verify the resistance is less than or equal to 2.5mΩ.

4.5 Electrical Bonding Test

The following bonding tests are provided for aircraft that have a GFC 500 Autopilot installed as
a requirement beyond any that may be given in the aircraft maintenance manual.
4.5.1 Requirements
All GFC 500 equipment must be installed. For the GMC 507, the tests are performed with the
connectors connected. For the GSA 28, tests are conducted with the connector disconnected.
Gain access for the procedure listed below in Section 4.5.3 as required and in accordance with
the aircraft maintenance manual. It is recommended that these tests are conducted after visual
inspection of the zone to minimize access requirements.
4.5.2 Test Equipment
A milliohm meter and Kelvin probes are recommended for this test. However, an alternate
method may be used to provide equivalent results by using the following procedure and a
standard voltmeter, power supply with adjustable current limit, and ammeter. The test set up for
this alternate method is described below.
All test equipment used for the bond checks must be calibrated.
1. Connect the positive lead of the power supply to airframe ground. Connect/touch the
positive lead of the voltmeter to the same point.
Ensure that the voltmeter and power supply probes do not touch, so as not to
induce contact resistance.
2. Touch negative lead of power supply to each of the test points listed while performing
Step 3. At each required point, configure the power supply to produce 1 amp before
measuring voltage. (Use an ammeter to ensure current is within minimum of 1 amp
±100 milliamp at each point). Do not allow the reference current to exceed 1.5 amps for
safety.
3. With the current set to 1A, the voltage reading will be the value of the bonding
resistance. Set the voltmeter to measure millivolts and null the reading. Measure the
voltage from airframe ground (step 1) to each required test points and record the
voltage. (Perform Step 2 at each required point and ensure that minimum of 1 amp
±100 milliamp is present when measuring the voltage.)
TIP: When a 1A current is used all the millivolt readings are the same as mΩ, and
required no further calculation of bond resistance. If 1 amp reference current cannot
GFC 500 Autopilot with ESP Part 23 AML STC Maintenance Manual
190-02291-01
NOTE
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