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Page 8-24 G3X Installation Manual – Post Installation Checkout and Calibration Procedures
Revision A 190-01115-01
8.3.7 Site Evaluation of Magnetic Disturbances for Magnetometer Calibration
Procedure
As mentioned in Section 8.3.3, the Magnetometer Calibration Procedure (Calibration Procedure C) must
be carried out at a site that is determined to be free of magnetic disturbances.
NOTE
Typically, a compass rose is an acceptable location to perform the magnetometer
calibration procedure. However, because not all compass roses are well maintained, even
an existing compass rose should be regularly evaluated using the method described here
to determine if it is free of magnetic disturbances. If evaluation of an existing compass
rose indicates that magnetic disturbances are present, then an alternative location must be
found to perform the Magnetometer Calibration Procedure.
A G3X-equipped airplane 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 G3X-equipped airplane installation used to evaluate the site must have already completed the
pitch/roll offset compensation procedure (Procedure B). However, prior completion of the Magnetometer
Calibration Procedure (Procedure C) is not required.
In order to evaluate a candidate site, the Magnetometer Calibration Procedure must be performed twice:
once turning clockwise around the site, and once turning counter-clockwise. Both times, the procedure
should be conducted as described in Section 8.3.3 of this document, with the exception of the direction of
turns around the site.
NOTE
Although Section 8.3.3 indicates that the Magnetometer Calibration Procedure should be
performed by making a series of clockwise turns around the site, the procedure can also
be performed by making counter-clockwise turns for the purpose of evaluating the site
for magnetic disturbances.
If, upon completion of the Magnetometer Calibration Procedure in both the clockwise and counter-
clockwise directions, 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 perform the procedure in both the
clockwise and counter-clockwise directions to ensure that the magnetometer sweeps over a large enough
area at the candidate site.
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.