190-02177-02 Rev. A
Garmin G1000 NXi Pilot’s Guide for the Cessna NAV III
SY
STEM
O
VER
VIEW
FLIGHT
INSTRUMENTS
EIS
AUDIO P
ANEL
& CNS
FLIGHT
MANA
GEMENT
HAZARD
AV
OID
ANCE
AFCS
ADDITIONAL FEA
TURES
APPENDICES
INDEX
14
SYSTEM OVERVIEW
The AHRS 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.
AHRS no-GPS
Mode
AHRS coast-on-gyros
until invalid
AHRS Normal
Mode
AHRS no-Mag
Mode
AHRS no-Mag/
no-Air Mode
Heading Invalid
Heading Invalid
Attitude/Heading Invalid
YES
YES
YES
NO
NO
NO
Air Data Available and Reliable?
Mag Data Available and Reliable?
YES
NO
Mag Data AND Air Data
Available and Reliable?
GPS Data Available and Reliable?
Figure 1-8 AHRS Operation
GPS INPUT FAILURE
NOTE:
In-flight initialization of ADAHRS/AHRS, when operating without any valid source of GPS data and at
true air speed values greater than approximately 200 knots, is not guaranteed. Under these rare conditions,
it is possible for in-flight ADAHRS/AHRS initialization to take an indefinite amount of time which would
result in an extended period of time where valid ADAHRS/AHRS outputs are unavailable.
The system provides two sources of GPS information. If a single GPS receiver fails, or if the information
provided from one of the GPS receivers is unreliable, the ADAHRS/AHRS seamlessly transitions to using
the other GPS receiver. An alert message informs the pilot of the use of the backup GPS path. If both GPS
inputs fail, the ADAHRS/AHRS continues to operate in reversionary No-GPS mode so long as the air data and
magnetometer inputs are available and valid.