Garmin GI 275 Maintenance Manual page 79

The following are potential causes for a failure of the engine run-up check:
• Vibration motion of AHRS and/or GMU 44B caused by neighboring equipment and/or supports
• Mounting screws and other hardware for AHRS and/or GMU 44B are not firmly attached
• AHRS connector is not firmly attached to unit
• Wiring connected to the remotely mounted AHRS or GMU 44B is not firmly secured to
supporting structure
• An engine/rotor is significantly out of balance
After the AHRS calibration is complete, the AHRS attitude and heading information displayed will
become valid within 1 minute of power-up in Normal mode.
5.7.1.6 Magnetic Interference Test
It is recommended to run the Magnetic Interference Test using the GI 275. Alternatively, the GMU 44
Location Survey Tool and a PC can be used in lieu of the GI 275 display. Refer to AHRS/Magnetometer
Installation Considerations (P/N 190-01051-00).
During the survey test sequence, it is required to use a stopwatch or watch with a second hand to measure
the time for turning equipment on and off.
Prepare the rotorcraft and GMU 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 rotorcraft
components and devices that may affect the operation of the GMU through movement of ferrous
metal parts or electrical inductance. Rotorcraft components included on the list will vary
depending on rotorcraft model. An example survey sequence is provided in Table 5-1.
2. Position the rotorcraft in a magnetically quiet area. This step may involve repositioning large
metal objects including rotorcraft and ground support equipment away from the survey area.
3. Before beginning the survey, ensure that all items listed on the test sequence are in their pre-
exercise states (e.g., control surfaces neutral, lights off).
For dual AHRS installations, the following procedure must be performed on each AHRS through the
display it is directly wired to. The test can be done simultaneously on each display. Follow the display
prompts.
1. Power on the display(s) in Configuration mode.
2. Navigate to the test page (Calibration/Test → Attitude/Heading → Interference Test).
3. Complete the Before Calibration steps listed on the display; touch Next after completing each step
to move to the next step.
4. Touch Start to start the procedure.
5. Perform each action on the Test Sequence List at its specified elapsed time and duration. This will
help ensure correct identification of magnetic field deviation sources after the survey is complete.
6. Monitor the magnetic field deviation percentage throughout the survey. If deviation levels exceed
thresholds, mark the survey sequence exercises during which these deviations occurred.
7. Touch Done when the test sequence is completed. The GI 275 will display a test Pass or Fail, the
worst-case percentage of magnetic interference, and the time stamp at which it occurred.
8. Repeat the procedure for each installed AHRS unit if they were not completed simultaneously.
9. If the check passes, no further action is required.
190-02246-C2
Rev. 3
GI 275 Part 27 AML STC Maintenance Manual
Page 5-19