System Maintenance Manual

Page 7-30 G1000/GFC700 System Maintenance Manual – C90A/C90GT/C90GTi King Air
Revision G 190-00682-01
7.7.3 Compass Rose Evaluation of Magnetic Disturbances for Magnetometer
Calibration Procedure (Optional)
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 G1000-equipped airplane that has completed the pitch/roll offset compensation procedure (Procedure
A-1, Section 7.7.2) 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.
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 7.7.4 of this document, with the exception of the direction of
turns around the site.
NOTE
Although Section 7.7.4 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 each clockwise and counter-clockwise
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 result 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.