|
|publisher=Air Safety Week
|date=August 14, 2006
}}</ref> An ADIRU isacts as a single, [[fault-tolerant design|fault tolerant]] source of attitude, air data and navigational data for both pilots of an aircraft.<ref name="art2">
{{Cite web
|url=http://www.findarticles.com/p/articles/mi_m0UBT/is_2005_May_9/ai_n13829607
|date=March 26, 2007
}}</ref>
<ref name="art3">
This device is used on various [[military aircraft]] as well as civilian [[airliner]]s starting with the [[Airbus A320]]<ref name="art3">
{{Cite web
|url=http://www.ainonline.com/Publications/farn/farn_02/farn_02d2_honeywellpg48.html
==Description==
An ADIRS consists of aup singleto three [[fault-tolerant design|fault tolerant]] ADIRUADIRUs located in the aircraft electronic rack, Aan SAARUassociated locatedcontrol nearby,and display unit (CDU) in the cockpit and remotely mounted [[air data module]]s (ADMs).<ref name="art1">
{{Cite web
|url=https://www.arinc.com/cf/store/catalog_detail.cfm?item_id=280
|df=dmy-all
}}
</ref> The 777No 3 ADIRU is a [[Redundancy (engineering)|redundant]] unit that may be selected to supply data to botheither the commander's andor the co-pilot's displays in the event of a partial or complete failure of multipleeither internalthe componentsNo of1 theor No 2 ADIRU. There is no cross-channel redundancy managementbetween inthe anyNos of1 theand ADIRU's2 userADIRUs, systemsas andNo the3 SAARUADIRU is the only alternate source of air and inertial reference data. An inertial reference (IR) fault in ADIRU No 1 or 2 will cause a loss of [[Angle of attack|attitude]] and navigation information on their associated [[EFIS#Primary flight display (PFD)|primary flight display]] (PFD) and navigation display (ND) screens. An air data reference (ADR) fault will cause the loss of airspeed and altitude information on the affected display. In either case the information can only be restored by selecting the No 3 ADIRU.<ref name="art5" />
Each ADIRU comprises an air data reference (ADR) and an inertial reference (IR) component.<ref name="urlA330 - Navigation">{{cite web|publisher=smartcockpit.com |url=http://www.smartcockpit.com/pdf/plane/airbus/A330/systems/0019/ |archive-url=https://archive.today/20070115043457/http://www.smartcockpit.com/pdf/plane/airbus/A330/systems/0019/ |url-status=dead |archive-date=15 January 2007 |title=Airline training guides, Aviation, Operations, Safety -Navigation A330 |access-date=12 June 2009 }}</ref>
===Air data reference===
{{See also|Pitot-static system}}
The air data reference (ADR) component of an ADIRU provides airspeed, [[Mach number]], angle of attack, temperature and barometric altitude data. Both the ADIRU and the SAARU transmit voted, high-availability, high-integrity air data to all user systems<ref name="aero-08">
{{cite web
|url=http://www.boeing.com/commercial/aeromagazine/aero_08/erroneous_textonly.html
==Complexity in redundancy==
Analysis of complex systems is itself so difficult as to be subject to errors in the certification process. Complex interactions between flight computers and ADIRU's can lead to counter-intuitive behaviour for the crew in the event of a failure. In the case of [[Qantas Flight 72]], the captain switched the source of IR data from ADIRU1 to ADIRU3 following a failure of ADIRU1; however ADIRU1 continued to supply ADR data to the captain's primary flight display. In addition, the master flight control computer (PRIM1) was switched from PRIM1 to PRIM2, then PRIM2 back to PRIM1, thereby creating a situation of uncertainty for the crew who did not know which redundant systems they were relying upon.<ref name="harmful">
However the ADIRU continued to supply ADR data to the pilots' primary flight displays.
{{cite web |url=http://www.dcs.gla.ac.uk/~johnson/papers/ISSC09/ADIRU_Accident_Submission.pdf |title=The Dangers of Interaction with Modular and Self-Healing Avionics Applications: Redundancy Considered Harmful |author1=C.W. Johnson |author2=C. Michael Holloway |date=2 February 2009 |access-date=8 June 2009}}</ref>
TheReliance ADIRUon doesredundancy notof requireaircraft maintenancesystems followingcan firstalso andlead secondto failuresdelays ofin it'sexecuting gyros,needed accelerometersrepairs, processors,as powerairline suppliesoperators orrely ARINCon interfaces.the redundancy Thisto allowskeep forthe deferredaircraft maintenancesystem of the ADIRUworking untilwithout ahaving suitableto timerepair andfaults ___locationimmediately.<ref name="art5"/><ref name="art2"/><ref name="gremlins"/><ref name="harmful"/>
{{cite web |url=http://www.dcs.gla.ac.uk/~johnson/papers/ISSC09/ADIRU_Accident_Submission.pdf |title=The Dangers of Interaction with Modular and Self-Healing Avionics Applications: Redundancy Considered Harmful |author1=C.W. Johnson |author2=C. Michael Holloway |date=2 February 2009 |access-date=8 June 2009}}</ref>
==Failures and directives==
| 