Ahrs Operation - Garmin G950 Pilot's Manual

AHRS OPERATION

Aggressive maneuvering while AHRS is not operating normally may degrade AHRS accuracy.
NOTE:
In addition to using internal sensors, the GRS 77 AHRS uses GPS information, magnetic field data and air
data to assist in attitude/heading calculations. In normal mode, the AHRS relies upon GPS and magnetic field
measurements. If either of these external measurements is unavailable or invalid, the AHRS uses air data
information for attitude determination. Four AHRS modes of operation are available (see Figure 1-14) and
depend upon the combination of available sensor inputs. Loss of air data, GPS, or magnetometer sensor inputs
is communicated to the pilot by message advisory alerts.
The AHRS (GRS 77) corrects for shifts and variations in the Earth' s magnetic field by applying the Magnetic
Field Variation Database. The Magnetic Field Variation Database is derived from the International Geomagnetic
Reference Field (IGRF). The IGRF is a mathematical model that describes the Earth' s main magnetic field and its
annual rate of change. The database is updated approximately every 5 years. See the Appendices for information
on updating the Magnetic Field Variation Database. The system will prompt you on startup when an update is
available. Failure to update this database could lead to erroneous heading information being displayed to the
pilot.
Mag Data Available and Reliable?
Y
E
S
AHRS Normal
Mode
Loss of GPS, magnetometer, or air data inputs is communicated to the pilot by message advisory alerts. Any
failure of the internal AHRS inertial sensors results in loss of attitude and heading information (indicated by red
'X' flags over the corresponding flight instruments).
190-00870-02 Rev. A
GPS Data Available and Reliable?
Y
E
S
N
O
Air Data Available and Reliable?
Y
E
S
AHRS no-Mag AHRS no-Mag/
Mode no-Air Mode
Heading Invalid Heading Invalid
Figure 1-10 AHRS Operation
Garmin G950 Pilot's Guide for the Pilatus PC-6
Mag Data AND Air Data
Available and Reliable?
Y
E
S
N
O
AHRS no-GPS
Mode
SYSTEM OVERVIEW
N
O
N
O
AHRS coast-on-gyros
until invalid
Attitude/Heading Invalid
13