PRIMUS
r
1000 Integrated Avionics System
A28--1146--112--00
AHZ--800 Attitude and Heading Reference System (AHRS)
A--8
Reduced Performance Operation
Two reduced performance modes are available: basic mode
for attitude, and DG mode for heading. The basic mode is annunciated
and entered automatically when true airspeed from the MADC
becomes invalid. The basic mode is annunciated by lighting a white
AHRS BASIC MODE message on the EICAS. AHRS basic mode
operation results in an attitude system that behaves like a conventional
vertical gyro (VG) with pitch and roll erection cutoffs. It is subject to drift
and acceleration errors. For this reason, AHRS in the basic mode
operates with reduced attitude accuracy.
The DG mode disables heading output automatic slaving. This mode
is entered by settomg the MAG/DG switch to DG. After the mode is
entered, the MAG annunciation on the PFD is replaced with a DG above
the compass display. AHRS DG mode operation acts like a free
directional gyro. It is subject to drift and turn error. For this reason, the
AHRS DG mode operates with reduced heading accuracy.
While in the DG mode, the heading card can be manually set to any
heading using the CW/CCW switch to enter an initial heading value.
The control can not be used in the slaved mode.
Moving the CW/CCW switch to CW increases the heading value. The
HDG flag on the HSI is displayed when a slew command is initiated, and
clears when the compass card reaches the selected heading. In the
DG mode, the system can be manually slaved using the cross--side
heading or standby compass as reference.
POWER--UP TEST
When AHRS power is applied, the system completes the power--up
test. On the ground, this test lasts two minutes. During this time, the
annunciations listed in table A--2 are displayed.
Annunciation
Location
ATT FAIL
In the PFD attitude sphere
HDG FAIL
On the PFD and MFD
Pilot Self--Test Annunciations
Table A--2
