AIR DATA INERTIAL REFERENCE SYSTEM
Purpose
The air data inertial reference system (ADIRS) has two primary
functions:
* Air data reference (ADR)
* Inertial reference (IR).
The ADR function calculates airspeed and barometric altitude.
The IR function calculates this data:
* Attitude
* Present position
* Groundspeed
* Heading.
Abbreviations and Acronyms
* AACU - antiskid autobrake control unit
* AC - alternating current
* A/D - analog to digital
* ADF - automatic direction finder
* ADI - attitude direction indication
* ADIRS - air data inertial reference system
* ADIRU - air data inertial reference unit
* ADM - air data module
* ADR - air data reference
* alt - altimeter
* alt - altitude
* AOA - angle of attack
* ARINC - Aeronautical Radio, inc.
* A/T - autothrottle
* ATC - air traffic control
* att - attitude
* bat - battery
* baro - barometric
* brt - brightness
* capt - captain
* CAS - computed airspeed
* CDS - common display system
* CDU - control display unit
* clr - clear
* CPC - cabin pressure controller
* CPU - central processing unit
* DC - direct current
* DEU - display electronics unit
* DU - display unit
* dspl - display
* EFIS - electronic flight instrument system
* elec - electronic
* elex - electrical
* ent - enter
* FCC - flight control computer
* FDAU - flight data acquisition unit
* FMC - flight management computer
* FMCS - flight management computer system
* F/O - first officer
* FPV - flight path vector
* FSEU - flap slat electronics unit
* FWD - forward
* GPS - global positioning system
* GPWC - ground proximity warning computer* GS - ground speed
* hdg - heading
* HPA - hecto-pascals
* IFSAU - integrated flight systems accessory unit
* in - inches
* init - initialization
* instr - instrument
* IR - inertial reference
* IRS - inertial reference system
* ISDU - inertial system display unit
* L - left
* LCD - liquid crystal display
* LSK - line select key
* MAG - magnetic
* MASI - mach airspeed indicator
* MCU - master caution unit
* MMR - multi-mode receiver
* MSU - mode select unit
* nav - navigation
* NCD - no computed data
* ND - navigation display
* NVM - non-volatile memory
* PPOS - present position
* pos - position
* PSEU - proximity switch electronics unit
* R - right
* ref - reference
* RMI - radio magnetic indicator
* R/T - receiver transmitter
* SAT - static air temperature
* sel - select
* SMYD - stall management yaw damper
* spd - speed
* stby - standby
* STS - status
* sw - switched
* sys - system
* TAS - true airspeed
* TAT - total air temperature
* TCAS - traffic collision avoidance system
* TK - track
* trk - track
* tru - true
* V - volts
* VOR - VHF omnidirectional range
* VSI - vertical speed indication
* WXR - weather radar
* xfr – transfer
ADIRS - GENERAL DESCRIPTION
General
The air data inertial reference system (ADIRS) supplies these
type of data to the aircrew and to the airplane systems:
* Altitude
* Airspeed
* Temperature
* Heading
* Attitude
* Present position.
The ADIRS has these components:
* Air data modules (ADMs) (4)
* Total air temperature (TAT) probe
* Angle of attack (AOA) sensors (2)
* Inertial system display unit (ISDU)
* Mode select unit (MSU)
* Air data inertial reference unit (ADIRU) (2)
* IRS master caution unit.
Functional Description
The TAT probe measures the outside air temperature. It
changes the temperature value to an electrical signal. The
electrical signal goes to the ADIRUs.
The AOA sensors measure and convert angle of attack to
electrical signals. The electrical signals go to the ADIRUs.
The ISDU supplies initial position and heading data to the
ADIRUs. It also supplies this data to the flight crew:
* Present position
* Heading
* Navigation
* Performance
* Status.
The MSU gives mode selection data to the ADIRUs. It also
shows system operational and fault status to the flight crew.
The two ADIRUs calculate and send air data and inertial
reference information on ARINC 429 data buses. Each ADIRU
has two parts. One part is the air data reference (ADR) part. The
other is the inertial reference (IR) part.
The ADIRUs use these inputs to calculate air data:
* Pitot pressure
* Static pressure
* Total air temperature
* Angle of attack
* Common display system (CDS) barometric correction
* IR data.
Each ADIRU uses three accelerometers and three laser gyros
to calculate inertial reference (IR) data. Initial present position
Information goes to the adirUs from the isdu, or the flight
management computer system (FMCS).
The IRS master caution unit sends fail discretes to the flight
compartment master caution system.
ADIRS - COMPONENT LOCATION - FLIGHT COMPARTMENT
General
These are the ADIRS components in the flight compartment:
* Inertial system display unit (ISDU)
* Mode select unit (MSU)
* IRS master caution annunciator.
These are the components in the flight compartment that have
an interface with the ADIRS:
* Left inboard and outboard display units
* Right inboard and outboard display units
* Upper center display unit
* IRS select switch
* Control display unit (CDU) 1 and 2
* Radio magnetic indicator (RMI)
* Left and right EFIS control panels.
ADIRS - COMPONENT LOCATION - IRS MASTER CAUTION UNIT
General
THE IRS master caution unit is in the flight compartment on the
P61 panel.
ADIRS - COMPONENT LOCATION - EE COMPARTMENT
General
These are the ADIRS components in the electronic equipment
(EE) compartment:
* Left air data inertial reference unit (ADIRU)
* Right ADIRU.
ADIRS - COMPONENT LOCATION - PITOT AIR DATA MODULES
General
The pitot pressure air data modules (ADM) are in the forward
equipment compartment.
ADIRS - COMPONENT LOCATION - STATIC AIR DATA MODULES
General
The static pressure ADMs are in the forward cargo
compartment, above the ceiling panels.
ADIRS - COMPONENT LOCATION - AOA SENSORS AND TAT PROBE
General
The angle of attack (AOA) sensors are on both sides of the
fuselage. The total air temperature (TAT) probe is on the left
side.
ADIRS – POWER
ADIRU
The ADIRU operates with 115v ac or 28v dc. 115v ac is the
normal power source.
Each ADIRU has a separate ac and dc power source. The left
ADIRU gets power from these buses:
* 115v ac stby bus
* 28v dc sw hot battery bus.
The right ADIRU gets power from these buses:
* 115v ac xfr bus 2
* 28v dc sw hot battery bus.
AC Reference Voltage
The 28v ac stby bus supplies a servo reference voltage to the
left ADIRU and to the left angle of attack (AOA) sensor. The 28v
ac xfr bus 2 supplies servo reference voltage to the right ADIRU
and to the right AOA sensor.
Integrated Flight Systems Accessory Unit
The integrated flight systems accessory unit (IFSAU) gets ac
power from the 115v ac xfr bus 2. DC power comes from the 28v
dc sw hot bat bus. The IFSAU uses these inputs to control power
going to the right ADIRU and to supply power to the crew call
horn when the ADIRUs operate with dc power on the ground.
Air Data Modules
The left ADIRU supplies 13.5v dc to the left pitot ADM and to the
left static ADM. The right ADIRU supplies 13.5v dc to the right
ADMs.
Inertial System Display Unit
The inertial system display unit (ISDU) gets 28v dc from the left
and the right ADIRU.
IRS Master Caution Unit
The IRS master caution unit gets power from the 28v dc bat bus.
ADIRS - DC POWER OPERATION
General
The ADIRUs operates with AC or DC power. AC power is the
normal power source. If the AC power source is not available,
DC power from the airplane battery will supply power to the
ADIRUs.
Left ADIRU DC Operation
When AC power is not available, the left ADIRU will operate on
DC power from the 28v dc sw hot battery bus. The left ADIRU
will continue to operate on DC power until the battery power is
less than 18v dc.
Right ADIRU DC Operation
DC power to the right ADIRU goes through a time delay circuit