# Air data computer

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{{Short description|Avionics component}}
{{this|air data computers in general|the specific CADC used in the F-14|F-14 CADC}}

thumb|Air data computer

An '''air data computer''' ('''ADC''') or '''central air data computer''' ('''CADC''') computes critical real-time flight data.<ref>{{cite book |last1=United States Joint Chiefs of Staff |title=The official dictionary of military terms |date=1988 |publisher=Science Information Resource Center, Hemisphere Publishing |isbn=0-89116-792-7 |page=63 |url=https://archive.org/details/officialdictiona00unit/page/63/mode/1up}}</ref> It is an essential [avionics](/source/avionics) component found in modern aircraft. This computer, rather than individual [instruments](/source/flight_instruments), can determine the [calibrated airspeed](/source/calibrated_airspeed), Mach number, altitude, and [altitude trend](/source/vertical_speed_indicator) data from pressure and temperature inputs from an aircraft's [pitot-static system](/source/pitot-static_system).<ref>{{cite magazine |url=http://www.aea.net/AvionicsNews/ANArchives/ADCJan05.pdf |title=Air Data Computer |magazine=Avionics News |author=Kim Wiolland |date=January 2015}}</ref><ref>{{cite web |url=http://www.wisegeek.com/what-is-an-air-data-computer.htm |title=What Is an Air Data Computer? |website=Wisegeek.com |access-date=2015-06-25}}</ref> In some very high-speed aircraft such as the [Space Shuttle](/source/Space_Shuttle), [equivalent airspeed](/source/equivalent_airspeed) is calculated instead of calibrated airspeed. Air data computers usually also have an input of [total air temperature](/source/total_air_temperature). This enables the computation of static air temperature and [true airspeed](/source/true_airspeed).

==Models==
In [Airbus](/source/Airbus) aircraft the air data computer is combined with attitude, heading and navigation sources in a single unit known as the [Air Data Inertial Reference Unit](/source/Air_Data_Inertial_Reference_Unit) (ADIRU) which has now been replaced by the [Global Navigation Air Data Inertial Reference System](/source/Global_Navigation_Air_Data_Inertial_Reference_System) (GNADIRS).<ref>{{cite web |url=https://termaviation.com/what-is-gnadirs-on-airbus-a320/ |title=What is GNADIRS on Airbus A320? (Global Navigation Air Data Inertial Reference System) |access-date=2024-09-24}}</ref>

On the Embraer [Embraer E-Jet family](/source/Embraer_E-Jet_family) the concept has been refined further by splitting air data acquisition and measurement{{snd}}performed by combined pitot and static ''air data smart probes'' with integrated sensors{{snd}}and computation of parameters performed by air data applications (ADA) executed on non-dedicated processing units. As all information from the sensors is transmitted electrically, routing of pitot and static pressure lines through the aircraft and associated maintenance tasks is avoided.<ref>Embraer 195 Airplane Operations Manual, Volume 2, chapter 14</ref>

In simpler aircraft and helicopters, the air data computers, generally two in number, and smaller, lighter and simpler than an ADIRU, may be called air data units, although their internal computational power is still significant. They commonly have the pitot and static pressure inputs, as well as [outside air temperature](/source/outside_air_temperature) from a [platinum resistance thermometer](/source/platinum_resistance_thermometer) and may control heating of the pitot tube and static vent to prevent blockage due to ice. On simpler aircraft, there is usually not a fly-by-wire system, so the outputs are typically to the cockpit altimeters or display system, flight data recorder and autopilot system. Output interfaces typically are [ARINC 429](/source/ARINC_429), [Gillham](/source/Gillham_code) or even [IEEE 1394](/source/IEEE_1394) (Firewire). The data provided may be true airspeed, pressure altitude, [density altitude](/source/density_altitude) and [Outside Air Temperature](/source/Outside_Air_Temperature) (OAT), but with no involvement in aircraft attitude or heading, as there are no [gyroscope](/source/gyroscope)s or [accelerometer](/source/accelerometer)s fitted internally. These devices are usually autonomous and do not require pilot input, merely sending continuously updated data to the recipient systems while the aircraft is powered up. Some, like the Enhanced Software Configurable Air Data Unit (ESCADU)<ref>{{Cite web |url=https://www.curtisswrightds.com/products/electronic-systems/air-data/escadu.html |title=ESCADU |access-date=2019-02-02 |archive-date=2018-10-11 |archive-url=https://web.archive.org/web/20181011085728/https://www.curtisswrightds.com/products/electronic-systems/air-data/escadu.html |url-status=dead }}</ref> are software configurable to suit many different aircraft applications.

Apart from commercial ADCs, there are available do-it-yourself, and open-source implementations.<ref>[https://hackaday.com/2018/01/25/asgard-the-open-source-air-data-computer/ Asgard: the Open Source Air Data Computer], [HACKADAY](/source/HACKADAY), Tom Nardi, 2018-01</ref>

==History==
thumb|The Bendix Central Air Data Computer contains complex electromechanical mechanisms.

Electrical-mechanical air data computers were developed in the early 1950s to provide a central source of airspeed, altitude, and other signals to avionic systems that needed this data. A central air data computer avoided duplication of sensing equipment and could be more sophisticated and accurate.<ref>{{cite journal |last1=Klass |first1=Philip |title=Single Computer Combines Flight Data |journal=Aviation Week |date=28 Sep 1953 |pages=45–48 |url=https://archive.org/details/Aviation_Week_1953-09-28/page/n24/mode/1up}}</ref> The first air data computer was built by Kollsman Instruments for the [B-52 bomber](/source/B-52_bomber).<ref>{{cite journal |title=From the first to the latest |journal=Air Force Magazine |issue=Nov 1985 |page=115}}</ref> [Bendix](/source/Bendix_Corporation) started producing a central air data computer in 1956 for use on US Air Force jet fighters.<ref>{{cite book |last1=Hamlin |first1=Fred |last2=Miller |first2=Eleanor |title=The Aircraft Year Book for 1956 |date=1957 |publisher=The Lincoln Press |location=Washington, DC |page=171 |url=https://www.aia-aerospace.org/wp-content/uploads/the-1956-aircraft-year-book.pdf}}</ref> [Garrett AiResearch](/source/Garrett_AiResearch) developed early central air data computer systems that integrated pneumatic, electrical, and electronic components.<ref>{{cite journal |title=Air Data Computer System |journal=Aviation Week |date=2 May 1955 |page=5 |url=https://archive.org/details/Aviation_Week_1955-05-02/page/n1/mode/2up}}</ref>

The late 1960s saw the introduction of digital air data computers. In 1967, Garrett AiResearch's ILAAS air data computer was the first all-digital unit.<ref>{{cite journal |title=Fly by the numbers |journal=Electronics |date=16 Oct 1967 |volume=40 |issue=21 |page=42 |url=https://www.worldradiohistory.com/Archive-Electronics/60s/67/Electronics-1967-10-16.pdf}}</ref> The [DC-10](/source/DC-10) used Honeywell's digital air data system in 1969<ref>{{cite journal |last1=Corey |first1=Frederick |title=DC-10's air data system casts a long shadow |journal=Electronics |date=17 Mar 1969 |volume=42 |issue=6 |pages=125–130 |url=https://www.worldradiohistory.com/Archive-Electronics/60s/69/Electronics-1969-03-17.pdf#page=127}}</ref> and the [F-14 CADC](/source/F-14_CADC) used on the [F-14](/source/F-14) in 1970 used custom [integrated circuit](/source/integrated_circuit)s.

From the late 1980s much of the [USAF](/source/USAF) and [USN](/source/USN) aircraft fleets were retrofitted with the [GEC Avionics](/source/GEC_Avionics) Rochester-developed Standard Central Air Data Computer (SCADC).<ref>{{cite journal|title=New Avionics Standardization Initiative - Standard Central Air Data Computer (SCADC)|journal=Feedback|year=1979 |volume=II|issue=1|page=3|url=https://archive.org/stream/feedback211980unit#page/2/mode/2up|publisher=Wright-Patterson Air Force Base}}</ref><ref>{{cite book|title=Standard Central Air Data Computer|date=1985|publisher=GEC Avionics|url=http://rochesteravionicarchives.co.uk/img/catalog/ZZ_1376744342_DDBR0298%20%28O%26A-1b%29.pdf|archive-date=2015-04-18|access-date=2022-10-19|archive-url=https://web.archive.org/web/20150418214637/http://rochesteravionicarchives.co.uk/img/catalog/ZZ_1376744342_DDBR0298%20%28O%26A-1b%29.pdf|url-status=dead}}</ref> Aircraft fitted included the [A-4 Skyhawk](/source/A-4_Skyhawk), [A-6 Intruder](/source/A-6_Intruder), [A-7 Corsair](/source/A-7_Corsair), [C-5A/B Galaxy](/source/C-5A%2FB_Galaxy), [EA-6B Prowler](/source/EA-6B_Prowler), [F-111 Aardvark](/source/F-111_Aardvark), [F-4 Phantom](/source/F-4_Phantom), [S-3 Viking](/source/S-3_Viking), [C-141 Starlifter](/source/C-141_Starlifter), [C-135 Stratolifter](/source/C-135_Stratolifter), [C-2 Greyhound](/source/C-2_Greyhound), and [E-2 Hawkeye](/source/E-2_Hawkeye),<ref>{{Cite web|url=https://rochesteravionicarchives.co.uk/document-archive/brochures/standard-central-air-data-computer-1|title=Standard Central Air Data Computer &#91;SCADC, 1987&#93; :: Rochester Avionic Archives}}</ref> for which the company received the [Queen's Award for Technological Achievement](/source/Queen's_Award_for_Technological_Achievement).<ref>{{Cite web|url=https://rochesteravionicarchives.co.uk/media-archive/video/isd-queen-s-award-ceremony|title = ISD Queen's Award Ceremony :: Rochester Avionic Archives}}</ref>

==See also==
* [Acronyms and abbreviations in avionics](/source/Acronyms_and_abbreviations_in_avionics)
* [F-14 Central Air Data Computer](/source/F-14_Central_Air_Data_Computer), used on the [F-14](/source/F-14)
* [Synthetic air data system](/source/Synthetic_air_data_system)

== References ==
{{reflist}}

{{Aircraft components}}

{{DEFAULTSORT:Air Data Computer}}
Category:Avionics
Category:Aircraft instruments
Category:Glass cockpit

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Adapted from the Wikipedia article [Air data computer](https://en.wikipedia.org/wiki/Air_data_computer) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Air_data_computer?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.