Garmin GI 275 Maintenance Manual page 81

5.7.1.7 Magnetometer Calibration
Use the compass rose or a calibrated magnetic sight compass to calibrate the magnetometer. Ensure the
rotorcraft and compass is located away from magnetic buildings, materials, and other structures. The
accuracy of the AHRS cannot be guaranteed if the calibration is not performed in an area that is free of
metallic structure or objects. Refer to Section 5.7.1.1 for guidance in evaluating a site for magnetic
disturbances.
NOTE
The Pitch/Roll Offset Compensation Procedure in Section 5.7.1.3 must be completed prior
to performing this procedure.
Performing the Magnetometer Calibration removes any previously stored heading offset values. For
multiple AHRS installations, the calibration can be done simultaneously using multiple displays.
1. Start the rotorcraft engine per the POH/RFM.
2. With all of the rotorcraft systems powered on and operating normally, position the rotorcraft on a
compass rose at a heading of 360° (Magnetic North), or select a level and magnetically clean
location and use a calibrated sight compass.
3. Power on the GI 275(s) in Configuration mode.
4. Navigate to the test page (Calibration/Test → Attitude/Heading → Calibrate Magnetometer).
5. Complete the Before Calibration steps listed on the display; touch Next after completing each step
to move to the next step.
6. Touch the Start button when it becomes available to start the calibration procedure.
7. Follow the on-screen commands to complete the calibration.
8. Repeat the steps 4 - 7 for each installed AHRS unit if not completed simultaneously.
A successful heading calibration point is a full 18-second countdown followed by instruction to move. Due
to the difficulties in executing smooth, accurate turns, the display may incorrectly interpret the approach
heading point and instruct to "HOLD POSITION" prior to full completion of a 36° turn. If this condition is
encountered, use outside references to complete the approximate 36° turn, instead of using the display
instructions of when to complete the turn (use the compass rose radial to make the 36° (±5°) turn
increments). Accurately completing each 36° heading point for the required time as instructed will result in
a successful calibration.
Due to high winds or excessive airframe vibration, the operator may encounter a condition where the
18-second countdown is restarted without full completion of the previous countdown. If this is experienced
more than once for a given heading point, the operator should begin turning to the next station
(approximately 36°). A minimum of two successful heading points per quadrant is required. It may
sometimes be required to hold at a station after a countdown restart. A maximum of 20 heading points are
allowed for the entire calibration procedure. If too many countdown restarts are encountered, the
calibration will fail with the message, "TOO MANY STATIONS".
190-02246-C2
Rev. 3
GI 275 Part 27 AML STC Maintenance Manual
Page 5-21