Garmin GI 275 Maintenance Manual page 82

5.7.1.8 Compass Swing
After the Magnetometer Calibration Procedure is completed, a compass swing must be performed to verify
the AHRS heading accuracy.
1. With all of the rotorcraft and avionics systems powered on and operating normally, position the
rotorcraft on a compass rose at a heading 360° (Magnetic North) or select a level and magnetically
clean location and use a calibrated sight compass.
2. With the GI 275 in Normal mode, hold the knob in to open the menu.
3. Navigate to the Units page (System → Units).
4. Toggle the Nav Angle field to Magnetic.
5. Close the menu.
6. Record the HDG value displayed on the display as indicated in Table 5-2.
7. Record the heading displayed on the standby compass and non-stabilized compass. Verify or
correct the standby compass deviation card.
8. Calculate the heading errors by subtracting the displayed (B) value from the actual (A) value for
each of the headings. If each heading displayed on the display (or display #1 and display #2) is at
or within ±3° of the actual heading, no further adjustments are necessary. If one or more of the
displayed heading values are outside this range, further calibration is needed.
9. If all calculated heading errors are between -5° and +5° inclusive, the heading offset procedure can
be used for the Heading Offset Compensation Procedure. Proceed to Section 5.7.1.9.
NOTE
If at least one Heading Error (A-B) is greater than 5°/less than –5°, DO NOT perform the
Heading Offset Procedure in Section 5.7.1.9 until the GMU 44B installation has been
physically corrected.
10. If at least one Heading Error (A-B) is greater than 5°/less than -5°, calculate the average error by
adding all errors and dividing by 12. This is the angle by which the GMU 44B must be physically
rotated to correct the installation.
11. Modify the installation to rotate the GMU 44B by the amount calculated in the previous step.
When looking down at the GMU 44B, rotate clockwise for positive values and counterclockwise
for negative values.
12. After physically correcting the GMU 44B installation, repeat the procedures in Section 5.7.1.7 and
Section 5.7.1.8.
190-02246-C2
Rev. 3
GI 275 Part 27 AML STC Maintenance Manual
Page 5-22