Air Data Inertial Reference Unit

Air Data Inertial Reference Unit (ADIRU) is an aircraft component.Cite web|url=http://acronyms.thefreedictionary.com/ADIRU|title=ADIRU|accessdate=2006-09-16|year=2005] It is a part of the integrated Air Data/Inertial Reference system (ADIRS) which consists of up to three Air Data/Inertial Reference Units (ADIRUs) located in the aircraft electronic rack, an associated Control and Display Unit (CDU) in the cockpit and remotely mounted Air Data Modules (ADMs).Cite web|url=https://www.arinc.com/cf/store/catalog_detail.cfm?item_id=280|title=738-3 Air Data and Inertial Reference System (ADIRS)|accessdate=2008-07-14|year=2008] The ADIRS system supplies air data (air speed and altitude) and inertial reference (position and attitude) information to the pilots' Electronic Flight Instrument System displays and other user systems on the aircraft, including, but not limited to, the engines, autopilot, flight control and landing gear systems..Cite web|url=http://findarticles.com/p/articles/mi_m0UBT/is_32_20/ai_n26957235|title=The Intricate Complexity Within An Immaculate Redundancy Concern|accessdate=2008-07-16|publisher=Air Safety Week|year=August 14, 2006] An ADIRU acts as a "single, fault tolerant" source for both pilots of an aircraft.Cite web|url=http://www.findarticles.com/p/articles/mi_m0UBT/is_2005_May_9/ai_n13829607|title=LookSmart's FindArticles - Safety Concern|accessdate=2006-09-16|year=2005] This device is used on the new Airbus aircraft.Cite web|url=http://www.ainonline.com/Publications/farn/farn_02/farn_02d2_honeywellpg48.html|title=Honeywell's ADIRU selected by Airbus|accessdate=2008-07-16|publisher=Aviation International News|year=2002]

The No 3 ADIRU is a standby unit only and in the event of a partial or complete failure of either the No 1 or No 2 ADIRU, the No 3 ADIRU may be selected to supply air data and/or inertial reference data to either the commander's or the co-pilot's displays. However, there is no cross-channel redundancy between the No 1 and 2 ADIRUs, No 3 ADIRU being the only alternate source of air and inertial reference data. An IR (Inertial Reference} fault in ADIRU No 1 or 2 will cause a loss of attitude and navigation information on their associated PFD (Primary Flight Display) and ND (Navigation Display) screens. An ADR (Air Data Reference) 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.Cite web|url=http://findarticles.com/p/articles/mi_m0UBT/is_32_20/ai_n26957235|title=The Intricate Complexity Within An Immaculate Redundancy Concern|accessdate=2008-07-16|publisher=Air Safety Week|year=August 14, 2006]

Working principle

Each ADIRU is divided into two parts, either of which can operate independently in case of a failure of the other. The Air Data Reference (ADR) part provides airspeed, angle of attack, temperature and barometric altitude data. The Inertial Reference (IR) part gives attitude, flight path vector, ground speed and positional data.Cite web|url=http://findarticles.com/p/articles/mi_m0UBT/is_32_20/ai_n26957235|title=The Intricate Complexity Within An Immaculate Redundancy Concern|accessdate=2008-07-16|publisher=Air Safety Week|year=August 14, 2006]

Air Data Reference

The pitot and static pressures are measured by small Air Data Modules (ADM) located as close as possible to the respective pressure sources (pitot and static probes). The ADMs transmit their pressures to the ADIRUs through ARINC 429 data buses.Cite web|url=http://www.boeing.com/commercial/aeromagazine/aero_08/erroneous_textonly.html|title=Erroneous Flight Instruments|accessdate=2008-07-14|publisher=Boeing Aero Magazine, Issue 08]

References