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Air data inertial reference unit

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The Air Data Inertial Reference Unit (ADIRU) is a key component of the integrated Air Data Inertial Reference System (ADIRS), which supplies air data (air speed and altitude) and inertial reference (position and attitude) information to the pilots' Electronic Flight Instrument System displays as well as other systems on the aircraft such as the engines, autopilot, flight control and landing gear systems.[1] An ADIRU acts as a single, fault tolerant source of navigational data for both pilots of an aircraft.[2] It may be complemented by a Secondary Attitude Air Data Reference Unit (SAARU), as in the Boeing 777 design.[3]

This device is used on various military aircraft as well as civilian airliners starting with the Airbus A320[4] and Boeing 777.[5]

Description

An ADIRS consists of up to three fault tolerant ADIRUs located in the aircraft electronic rack, an associated Control and Display Unit (CDU) in the cockpit and remotely mounted Air Data Modules (ADMs).[6] The No 3 ADIRU is a standby unit that may be selected to supply data to either the commander's or the co-pilot's displays in the event of a partial or complete failure of either the No 1 or No 2 ADIRU. There is no cross-channel redundancy between the Nos 1 and 2 ADIRUs, as No 3 ADIRU 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 attitude and navigation information on their associated Primary Flight Display (PFD) and Navigation Display (ND) 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.[1]

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.[1] The ring laser gyroscope is the core enabling technology in the system, and is used together with accelerometers, pitots and other sensors to provide raw data.[7] The primary benefits of a ring laser over older mechanical gyroscopes is that there are no moving parts, it is rugged and lightweight, frictionless and does not resist a change in precession.

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.[4]

Failures and directives

  • May 3, 2000 - FAA Airworthiness directive 2000-07-27 was issued, addressing dual critical failures during flight, attributed to power supply issues affecting early Honeywell HG2030 and HG2050 ADIRU ring laser gyros used on several Boeing 737, 757, Airbus A319, A320, A321, A330, and A340 models.[2][8][9]
  • January 27, 2004 - FAA Airworthiness directive 2003-26-03 (later superseded by AD 2008-17-12) called for modification to the mounting of ADIRU3 to prevent failure and loss of critical attitude and airspeed data.[2] [10]
  • 25 June 2005 - An Alitalia Airbus A320-200 registered as I-BIKE departed Milan with a defective ADIRU as permitted by the Minimum Equipment List. While approaching London Heathrow Airport during deteriorating weather another ADIRU failed, leaving only one operable. In the subsequent confusion the third was inadvertently reset, losing its reference heading and disabling several automatic functions. The crew was able to effect a safe landing after declaring a Pan-pan.[11]
  • 1 August 2005 - Malaysia Airlines Flight 124, a Boeing 777-2H6ER departed Perth, Western Australia for Kuala Lumpur. Climbing through 38,000 feet a faulty accelerometer caused the aircraft's ADIRU and autopilot to command changes of altitude. The flight crew overrode the system and manually returned to land the aircraft at Perth. The subsequent ATSB investigation led the US FAA to issue emergency airworthiness directive 2005-18-51 on the fly-by-wire software.[12]
  • 6 August 2008 - The FAA issued airworthiness directive 2008-17-12 expanding on the requirements of the earlier AD 2003-26-03 which had been determined to be an insufficient remedy. In some cases it called for replacement of ADIRUs with newer models, but allowed 46 months from October 2008 to implement the directive.[13]
  • 7 October 2008 - Qantas Airlines Flight 72, an Airbus A330 departed Singapore for Perth. Some time into the flight, while cruising at 37,000ft, a failure in the No.1 ADIRU led to the autopilot automatically disengaging followed by two sudden uncommanded pitch down manoeuvres, according to the Australian Transport Safety Bureau (ATSB). The accident injured up to 74 passengers and crew, ranging from minor to serious injuries. The aircraft was able to make an emergency landing without further injuries. The aircraft was equipped with a Northrop Grumman made ADIRS, which investigators sent to the manufacturer for further testing.[14][15]
  • 15 January 2009 - The EASA issues Emergency Airworthiness Directive No 2009-0012-E to address the above A330 and A340 Northrop-Grumman ADIRU problem of incorrectly responding to a defective inertial reference.

References

  1. ^ a b c "The intricate complexity within an immaculate redundancy concern". Air Safety Week. August 14, 2006. Retrieved 2008-07-16.
  2. ^ a b c "Safety concern". Air Safety Week. May 5, 2005. Retrieved 2006-09-16.
  3. ^ "In the grip of the gremlins". Air Safety Week. March 26, 2007.
  4. ^ a b "Honeywell's ADIRU selected by Airbus". Farnborough: Aviation International News via archive.org. 22—28 July 2002. Retrieved 2008-07-16. {{cite web}}: Check date values in: |date= (help) Cite error: The named reference "art3" was defined multiple times with different content (see the help page).
  5. ^ Digital Avionics Systems. IEEE, AIAA. 1995. ISBN 0780330501. Retrieved 2008-10-16.
  6. ^ "738-3 Air Data and Inertial Reference System (ADIRS)". ARINC. 2008. Retrieved 2008-07-14.
  7. ^ International Aerospace Abstracts. Cambridge Scientific Abstracts, Inc, American Institute of Aeronautics and Astronautics. 1985. Retrieved 2008-10-16.
  8. ^ "Various transport category airplanes equipped with certain Honeywell Air Data Inertial Reference Units". US Federal Aviation Authority. April 18, 2000. Retrieved 2008-10-15.
  9. ^ "AD/INST/45 Honeywell Air Data Inertial Reference Units 6/2000 DM" (PDF). Australian Civil Aviation Safety Authority. April 27, 2000.
  10. ^ "Airbus model A318, A319, A320, and A321 series airplanes equipped with certain Northrop Grumman (formerly Litton) Air Data Inertial Reference Units". US Federal Aviation Authority. August 6, 2008. Retrieved 2008-10-15.
  11. ^ "AAIB Bulletin: 6/2006" (PDF). UK Air Accidents Investigation Branch. 2006. Retrieved 2008-10-15.
  12. ^ "Incident 20050801-1". Aviation Safety Network. Retrieved 2008-10-14.
  13. ^ "AD 2008-17-12 Airbus" (PDF). US Federal Aviation Authority. 6 August 2008. Retrieved 2008-10-16.
  14. ^ "Computer error behind Qantas midair drama". Australian Broadcasting Corporation. 14 October 2008. Retrieved 2008-10-15.
  15. ^ Steve Creedy (17 October 2008). "US tests on false data sent on Qantas jet over WA". The Australian.

Further reading

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