Page 15-40
G900X/G950 Installation and Maintenance Manual – Software, Configuration, and Calibration
Revision D
190-00719-00
15.4.3.2 Final GRS 77/GMU 44 Calibration Procedures
The Magnetometer Calibration Procedure (Calibration Procedure B) must be carried out at a site that is
determined to be free of magnetic disturbances. If it is unsure whether the site is ‘clean’ the technician
should verify that the site is ‘clean’ by following the guidance provided in Section 15.4.3.3. The
technician may skip Section 15.4.3.3 if the site condition is acceptable.
15.4.3.3 Site 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 G900X/G950-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 airplane 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 as described in Section 15.4.3.4 of this document, with the exception of the direction
of turns around the site.
NOTE
Although Section 15.4.3.4 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.