Garmin GI 275 Installation Manual page 141

Performing the Magnetic Interference Test
This section describes the setup and procedure required to successfully complete the GMU location survey
using the GI 275.
Prepare the aircraft and GMU 11/44B for the location survey by completing the following steps:
1. Prepare a detailed Test Sequence List with start and stop times for exercising all aircraft
components and devices that may affect the operation of the GMU through movement of ferrous
metal parts or electrical inductance. Aircraft components included on the list will vary depending
on aircraft model. An example survey sequence is provided in Table 4-6.
2. Position the aircraft in a magnetically quiet area. This step may involve repositioning large metal
objects including aircraft and ground support equipment away from the survey area.
3. Position the GMU in the aircraft location to be surveyed following the guidance in
Section 4.6.1. Secure using non-ferrous material, if necessary.
CAUTION
Do not permanently install the GMU prior to successfully completing the Magnetic
Interference Test. An unsurveyed location may be unsuitable for permanent installation
and cause the GMU to function incorrectly.
Before beginning the survey, ensure that all items listed on the test sequence are in their pre-exercise states
(e.g., control surfaces neutral, flaps up, lights off). Perform the survey by completing the following steps:
1. Connect the test harness to the GI 275 and GMU as shown in Figure 4-26.
2. Power up the aircraft (master switch, avionics bus, etc.).
3. Power on the GI 275 in Configuration mode (refer to Section 5.1.1).
4. If prompted, set the Unit ID per Section 5.3.1.
5. Navigate to the Interfaces page from the Configuration mode home page.
6. Configure AHRS 1 per Section 5.4.4.
7. Perform the Magnetic Interference Test per the instructions in Section 6.4.4.
If the check fails, the installation is considered unreliable until the source of magnetic interference is
identified and fixed. The Magnetometer Interference Test must be repeated until passed. When the
Magnetometer Interference Test fails, record the three magnetometer maximum deviation values and their
corresponding timestamps. A maximum deviation value greater than 5.0 mGauss in either the X or Y axes,
or greater than 8.0 mGauss in the Z axis, indicates a problem that must be resolved. Compare the
corresponding timestamps with the prepared test sequence to identify which action produced the failure.
Contact Garmin Support for assistance.
Three common reasons for a failed Magnetometer Interference Test are:
• Equipment, wiring, or ferro-magnetic items are installed too close to the magnetometer
• An electronic device has become grounded through the aircraft structure instead of the proper
ground wire in a twisted shielded pair, especially if the ground return path through the aircraft
structure passes near the GMU 11/44B
• The Interference Test was not run for a long enough duration. At least 25 seconds are required for
the test to properly complete
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Rev. 11
GI 275 Part 23 AML STC Installation Manual
Page 4-40