190-02081-03
GFC 600H HFCS Part 27 STC Maintenance Manual
Rev. 3
Page 7-19
7.7.5 GRS 79H or GSU 75H & GMU 44( ) Heading Offset Calibration
The Heading Offset Compensation procedure is not required if it was determined in Section 7.7.4 that all
calculated heading errors are between -3° and + 3° inclusive. It is recommended to perform the Heading
Offset Compensation procedure ONLY if the calculated heading errors indicate a constant (i.e., same
direction and same approximate magnitude) heading offset at all headings around the compass rose, not
exceeding 5° in magnitude. Otherwise, physically correct the GMU 44( ) installation and repeat the
Magnetometer Calibration procedure.
NOTE
If the Heading Offset Compensation Procedure must be performed on both AHRS #1 and
AHRS #2, it is permitted to run the procedure below simultaneously on two displays.
1. Start the aircraft engine in accordance with the aircraft RFM.
2. Power the displays on in Configuration mode.
3. Select
Heading Offset
from the Procedure menu (
Home → Calibration/Test → Attitude/
Heading
).
4. Select the desired AHRS unit to calibrate from the AHRS Unit selection.
5. Complete the Before Calibration steps listed on the display; select each step when complete so that
a green checkmark appears next to the selection.
6. Select the
Calibrate
button when it becomes active to start the calibration procedure.
7. Follow the on-screen commands to complete the calibration.
7.7.6 Site Evaluation of Magnetic Disturbances
Typically, a compass rose is an acceptable location to perform the magnetometer calibration procedure.
However, even an existing compass rose can be evaluated to determine if it is free of magnetic
disturbances. If the evaluation of an existing compass rose indicates that magnetic disturbances are present,
an alternative location must be found to perform the magnetometer calibration procedure.
A G500H TXi equipped aircraft can be used to evaluate a candidate site for magnetic disturbances and
determine whether it is a suitable location to perform the magnetometer calibration procedure. The
magnetometer calibration procedure itself contains the logic to simultaneously survey the location for
magnetic cleanliness while it is computing the magnetometer calibration parameters.
The G500H TXi equipped aircraft used to evaluate the site must have already completed the Pitch/Roll
Offset Compensation Procedure (Section 7.7.1). The completion of the magnetometer calibration
procedure (Section 7.7.3) is not required. To evaluate a site, the magnetometer calibration procedure must
be performed twice: once turning clockwise around the site and once turning counterclockwise. Both
times, the procedure should be conducted as described in Section 7.7.4 except for the direction of turns
around the site.
If, upon completion of the magnetometer calibration procedure in each clockwise and counterclockwise
direction, the PFD displays the “CALIBRATION SUCCESSFUL/SITE IS CLEAN” message, then the
candidate site is sufficiently free of magnetic disturbances and is acceptable for performing the
Magnetometer Calibration Procedure. It is important to obtain successful results in both the clockwise and
counterclockwise directions.
If, upon completion of the magnetometer calibration procedure in either of the two directions, the PFD
displays either the “MAG FIELD AT SITE NOT UNIFORM” or “MAG FIELD AT SITE DIFFERS
FROM IGRF MODEL” message, then the site contains magnetic disturbances that are too large, and an
alternate site should be used for the AHRS magnetic calibration.