AIRPLANE
OPERATIONS
MANUAL
NAVIGATION AND
COMMUNICATION
MARCH 30, 2001
2-18-30
Page
5
Code
01
AH-800 OPERATING MODES
The AHRS has six fundamental operating modes, which are described
below.
− Initialization mode: The Initialization Mode is entered upon power
up of the system. During the operation in this mode the AHRS
performs self-tests to determine the condition of its components
(sensors, AHC, power supply, etc). Furthermore the AHRS performs
a first order leveling process to determine pitch and roll, and further
slaves the magnetic heading to the flux valve. At the end of the
Initialization Mode the system enters the Full Performance Mode,
unless the crew selects the DG Mode or the system detects a lack of
input, in this case reverting automatically to the Basic Mode.
− Full Performance Mode: The Full Performance Mode (slaved) is
the standard system operating configuration. When operating in this
mode, the TAS input from the ADC is used in the vertical channel
(pitch and roll) to produce a Schuler tuned erection loop for pitch and
roll attitude, and the flux valve is used as a continuous heading
reference.
NOTE: When switched from DG to SLVD (Full Performance Mode)
the system performs automatic synchronization to the flux
valve.
− DG Mode: The DG Mode, which causes the heading channel to
operate as a free non-slaved gyro, is selected by the flight crew and
is used when operating in charted areas of unreliable magnetic
heading or in case of a failure in the flux valve.
− Basic Mode: The Basic Mode is entered automatically by the system
if the TAS becomes invalid. AHRS attitude output in this mode is
corrected by a simple first-order erection loop similar to that of a
conventional vertical gyro.
− Test Mode: The Test Mode is to be operated mainly by the ground
personnel during maintenance procedures. This mode is activated
through a switch located in the maintenance panel behind the pilot
seat when the airplane is on the ground. During the test, the system
verifies the outputs for proper operation of the data channels,
interconnections and indications.
− Maintenance Mode: The Maintenance Mode is used for
maintenance purposes only.
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