Pilot's Guide

190-00663-03 Rev. A

Garmin G1000 Pilot’s Guide for the Beechcraft C90A/GT/GTi

SYSTEM OVERVIEW

AHRS OPERATION

NOTE: Aggressive maneuvering while AHRS is not operating normally may degrade AHRS accuracy.

In addition to using internal sensors, the 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 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 ﬁve 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.

GRS 77 OPERATION

In normal mode, the GRS 77 AHRS relies upon GPS and magnetic ﬁeld measurements (air data is not used).

If one or more of these three external inputs is unavailable or unreliable, the AHRS uses the remaining inputs

for attitude/heading determination. Four AHRS modes of operation are available (Figure 1-13) 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.

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

Air Data Available and Reliable?

Mag Data Available and Reliable?

Mag Data AND Air Data

Available and Reliable?

GPS Data Available and Reliable?

Figure 1-13 AHRS Modes (GRS 77)