ADIRS AND STBY INSTRUMENTS PRESENTATION OF AIRBUS
GENERAL SYSTEM
The Airbus Single Aisle aircraft family includes several different types
of navigation systems, each used for particular functions. The systems
will be explained in separate groups based on their functions. These
functions are broken down into 4 main groups. They will be presented
in separate modules:
- Air Data/Inertial Reference System (ADIRS) and standby instruments,
- dependent position determining systems,
- landing aids,
- independent position determining systems.
There are several subsystems within each group.
The first group includes:
- Air Data Inertial Reference Units (ADIRUs),
- Standby Instruments,
- Digital Distance and Radio Magnetic Indicator (DDRMI) (optionally
removed for Thalès equipment only),
- Integrated Standby Instrument System (ISIS).
The second group (dependent position determining systems) includes:
- GPS,
- ATC/Traffic Alert and Collision Avoidance System (TCAS),
- DME,
- ADF,
- VOR.
The third group (landing aids) includes:
- ILS,
- marker receivers.
The fourth group (independent position determining systems) includes:
- Enhanced Ground Proximity Warning System (EGPWS),
- RAs,
- Weather Radar (WXR) and Predictive Windshear (PWS).
GENERAL SYSTEM
AIR DATA/INERTIAL REFERENCE SYSTEM
The aircraft has three identical and interchangeable ADIRUs.
Each ADIRU combines computers that carry out two functions in a single
unit with a shared power supply. Those computers are:
- an Air Data Reference (ADR) unit,
- a strapdown Inertial Reference (IR) unit, using laser gyros and
accelerometers.
The ADR and IR systems of each ADIRU operate independently, and a
failure of one system does not affect the other one.
AIR DATA INPUTS
The ADIRS systems have peripheral components connected to the
LRUs. These components are an integral part of the Air Data
portion. The components are:
- pitot probes,
- static ports,
- Angle of Attack Sensors (AOA),
- Total Air Temperature Sensor (TAT).
AIR DATA SECTION
The ADR part supplies various air data parameters to the EFIS
instruments and other users:
- airspeed, mach number, barometric altitude to the PFD and overspeed
to the Flight Warning Computer (FWC),
- TAT, Static Air Temperature (SAT), and AOA to other indicators
and users.
INERTIAL REFERENCE SECTION
The IR part of the ADIRU uses laser gyros and accelerometers. They
give inertial data to the EFIS, Flight Management and Guidance
Computers (FMGCs) and other users. Each ADIRU provides:
- attitude, heading, Vertical Speed (V/S), flight path vector to the PFD,
- heading, ground speed to the ND,
- IR position to FMGCs for A/C position computation. This
information is available on the MCDU DATA page.
ADIRS CONTROL AND INDICATING
The three ADIRUs are controlled through the single ADIRS Mode
Selector Unit (MSU) installed on the overhead panel.
The initialization of the ADIRUs is normally done through either one
of the two MCDUs installed on the center pedestal.
The Digital Distance Radio Magnetic Indicator (DDRMI) is optionally
installed on the main instrument panel below the standby instruments.
It supplies digital DME distance information, as well as heading
coming from ADIRS, and VOR/ADF bearing information.
PFD AND ND INDICATING
ADIRU 1 supplies the CAPT PFD and ND, and ADIRU 2 supplies
the F/O PFD and ND.
ADIRU 3 is used as a hot spare, and can be switched via the switching
panel to replace either ADIRU 1 or ADIRU 2. Each part of the
ADIRU (ADR or IR), can be indepentdently switched.
STANDBY INSTRUMENTS(OPTIONAL)
In case of EFIS system failures, the standby instruments can be used.
There are 3 conventional standby instruments, installed on the instrument
panel:
- airspeed indicator,
- altimeter,
- horizon.
The optional standby compass is installed just below the overhead panel
INTEGRATED STANDBY INSTRUMENT SYSTEM
The enhanced standby instrument, called ISIS (Integrated Standby
Instrument System), is installed on the instrument panel near the ECAM.
It replaces the 3 conventional standby instruments. The inputs to the
airspeed indication and the altimeter come directly from the air sources
(standby pitot probe and static ports). The standby horizon is
self-contained. ISIS is also capable of displaying heading and ILS
information. The standby compass is installed just below the overhead
panel.
COMPONENT LOCATION
Here is the location of the 3 ADIRUs.
MAINTENANCE/TEST FACILITIES
All the navigation systems can be tested from the MCDUs except the
ISIS.
ISIS tests and OTHER DATA are accomplished directly from the unit
itself.
SAFETY PRECAUTIONS
When you work on A/C, make sure that you obey all the Aircraft
Maintenance Manual (AMM) procedures. This will prevent injury to
persons and/or damage to the A/C.
Before you do the test of the probes, remove the protective covers. Do
not continue the test for more than one minute to prevent damage.
Do not touch the probes immediately after the test, they are hot.
