AIRPLANE
OPERATIONS
MANUAL
NAVIGATION AND
COMMUNICATION
REVISION 25
2-18-30
Page
11
Code
01
AH-900 OPERATING MODES
ALIGNMENT MODE
The alignment mode initiates when the airplane is energized. The
AHRU aligns its reference axis to the local vertical and true north, and
estimates the horizontal earth rate components to compute latitude.
The latitude at which the AHRU is aligned affects the alignment time.
The relationship between alignment time and latitude is shown in the
chart below.
0
5
10
15
20
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
ALIGNMENT TIME - minutes.....
ALIGNMENT LATITUDE - degrees Northern and Southern
The airplane must remain stationary during alignment (AHRS 1 (2)
ALN advisory message presented on the EICAS). If the AHRU detects
excessive airplane motion (AHRS 1 (2) EXC MOTION advisory
message is presented on the EICAS), it starts an automatic full
realignment 30±1 seconds after the motion stops. Normal passenger-
loading or cargo-loading activities should not cause excessive airplane
motion condition.
NOTE: To complete the alignment, the AHRU requires a valid input of
the airplane’s present position (latitude and longitude) from the
FMS or optionally through the MFD 1. The present position
input through MFD 1 bezel is possible only in airplanes
equipped with EICAS 18.5 and on.
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