Ahrs Operation; Gps Input Failure; Air Data Input Failure; Magnetometer Failure - Garmin G1000 Reference Manual

SECTION 1 – INTRODUCTION

1.7 AHRS OPERATION

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 (prima-
ry) 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 opera-
tion are available (see table below) 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.

GPS Input Failure

The G1000 system provides two sources of GPS infor-
mation. If a single GPS receiver fails, or if the informa-
tion provided from one of the GPS receivers is unreliable,
the 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 AHRS
continues to operate in reversionary 'No GPS' mode so
long as the air data and magnetometer inputs are available
and valid.
AHRS Mode
Normal/Primary
Reversionary:
No GPS
Reversionary:
No Magnetometer
Reversionary:
No Magnetometer
No Air Data
12
Available AHRS Functions
Pitch Roll Heading
X X X
X X X
X X -
X X -
Garmin G1000 Cockpit Reference Guide for Cessna Nav III

Air Data Input Failure

A failure of the air data input has no effect on AHRS
output while AHRS is operating in normal/primary mode.
A failure of the air data input while the AHRS is operating
in reversionary 'No GPS' mode results in invalid attitude
and heading information on the PFD (as indicated by red
'X' flags).

Magnetometer Failure

If the magnetometer input fails, the AHRS transitions
to one of the reversionary 'No Magnetometer' modes and
continues to output valid attitude information. However,
the heading output on the PFD does become invalid (as
indicated by a red 'X').
NOTE: Please refer to the Annunciations and
Alerts Pilot's Guide for specific AHRS alert infor-
mation.
NOTE: Pilots should be aware that aggressive
maneuvering in any of the three reversionary
modes listed below can degrade AHRS accu-
racy.
Available Sensor Inputs
GPS Input GMU 44
(At least one) Magnetometer
X X
- X
X -
X -
GDC 74A
Air Data Computer
X
X
X
-