Garmin CIRRUS PERSPECTIVE SR20 Line Maintenance Manual page 209

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7.4.3.2 Procedure B: GMU 44 Magnetometer Calibration Procedure
The Magnetometer Calibration Procedure must be carried out at a site that is free of magnetic
disturbances. A site evaluation for magnetic disturbances can be performed for the
magnetometer calibration procedure if a compass rose is not available. The accuracy of the
GRS 77 and GMU 44 cannot be guaranteed if this calibration is not performed in a magnetically
clean area.
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 procedure.
A Perspective™ System 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 Perspective equipped aircraft used to evaluate the
site must have already completed the pitch/roll offset compensation procedure (Procedure A).
However, prior completion of the magnetometer calibration procedure (Procedure B) 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 with the exception of the direction of turns
around the site.
Although the 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 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 procedure. It is important to obtain successful results in both the clockwise and
counter‐clockwise directions to ensure that the magnetometer sweeps over a large enough
area in the candidate site.
Cirrus Perspective™ Line Maintenance Manual
190-00920-00
NOTE
NOTE
Page 7-35
Rev. E