I A P 2 0 2 3 . 0 0 1 - A F M / I R I S T E X A N I I P A G E | 81
FOR SIMULATION USE ONLY – NOT A TRAINING AID
DATA BUSES
The aircraft is fitted with several data buses for transmission of electronic signals
and data between the various integrated systems such as the integrated avionics
computer (IAC), engine data manager (EDM), air data computer (ADC), power
management unit (PMU), global positioning system (GPS), very high frequency
navigation (VHF NAV), audio management unit (AMU), integrated data acquisition
recording system (IDARS), and others.
Each data bus provides one channel (PMU, IDARS) or two channels, A and B (all
others) for each connected system or unit. The two channels provide system and
signal redundancy. If either channel fails, the remaining channel provides all the
necessary data to the connected systems.
INERTIAL REFERENCE SYSTEM (IRS)
An inertial reference system (IRS) is installed to provide aircraft attitude (pitch, roll,
heading, turn and slip indication, accelerations, velocities), position, and time. The
IRS also provides standalone inertial navigation position when standalone GPS
navigation is not possible.
The IRS is equipped with a strap-down ring laser gyroscope sensor that measures
accelerations and calculates aircraft position. At system start-up, IRS uses GPS
information to begin its alignment. If GPS information is not available or unreliable,
the aircraft position (latitude and longitude) must be entered manually for the
alignment sequence to begin.
The IRS degrade (IRS DEGD) message on the EICAS display indicates that the
IRS/GPS hybrid operational mode is degraded, which in turn will cause some HUD
symbology to be missing should it remain illuminated. The IRS DEGD message
should extinguish approximately 90 seconds after IRS transitions from ALIGN to
NAV status.
NOTE
Taxi should be delayed until IRS DEGD message is extinguished.
The IRS DEGD message indicates a precision navigation solution is not available for
tactical training modes (A/A, A/G). Basic student mode avionics, except for HUD
FPM/CDM and ground track on the TSD, will continue to work normally with IRS
DEGD.
Failure of the IRS DEGD message to extinguish may require the IRS to be reset.
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