Gillham code: Difference between revisions

Revision as of 00:07, 8 August 2020

Revision as of 22:25, 15 August 2020

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The ''Gillham interface'' and ''code'' are an outgrowth of the 12-bit [[IFF Mark X]] system, which was introduced in the 1950s. The civil [[transponder interrogation mode (aviation)|transponder interrogation mode]]s [[Mode A|A]] and [[Mode C|C]] were defined in [[air traffic control]] (ATC) and [[secondary surveillance radar]] (SSR) in 1960.<!-- source needed! -->

{{anchor|Gillham}}The code is named after Ronald Lionel Gillham, a signals officer at Air Navigational Services, [[Ministry of Transport and Civil Aviation (United Kingdom)|Ministry of Transport and Civil Aviation]], who had been appointed a civil member of the [[Most Excellent Order of the British Empire]] (MBE)<!-- unclear if this was related to his involvement with this code, or for some other achievements --> in the Queen's [[1955 Birthday Honours]].<ref name="LG_1955-06-03"/> He was the UK's representative to the [[International Air Transport Association]] (IATA) committee developing the specification for the second generation of air traffic control system, known in the UK as "Plan Ahead", and is said to have had the idea of using a modified Gray code.<!--ref while having a family dinner. --><!-- Reportedly hegroup="nb" name="suddenlyNB_Anecdote" died in March 1968. --/> The final code variant was developed in late 1961<ref name="Ashley_1961"/> for the ICAO Communications Division meeting (VII COM) held in January/February 1962,<ref name="IEEE_1983"/> and described in a 1962 [[FAA]] report.<ref name="FAA_1962"/><ref name="FAA_1962_T6"/><ref name="FI_1964"/> The exact timeframe and circumstances of the term ''Gillham code'' being coined are unclear, but by 1963<!-- not a specific date, just the earliest source using the term I could find so far. --> the code was already recognized under this name.<ref name="CS_1963"/><ref name="CE_1963"/> By the mid-1960s the code was also known as ''MOA–Gillham code''<ref name="Wheeler_1969"/> or ''ICAO–Gillham code''. ''ARINC 572'' specified the code as well in 1968.<ref name="ARINC_572"/><ref name="ARINC_572-1"/>

Once recommended by the [[ICAO]] for automatic height transmission for air traffic control purposes,<ref name="FI_1964"/><ref name="Wightman_2017"/> it is now discouraged<ref name="Tooley-Wyatt_2009"/> and has been mostly replaced by modern serial communication in newer aircraft.

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* [[Flight level]]

* [[ARINC 429]]

==Notes==

{{Reflist|group="nb"|refs=

<ref group="nb" name="NB_Anecdote">Anecdotally, Ronald Lionel Gillham had the idea for the modified Gray code while having a family dinner. Reportedly, he died in March 1968.{{cn|date=August 2020|reason=The family dinner story and Gillham's date of death were already part of the article's body between 2009 and 2011, when they, together with other parts of the story, were removed for being unreferenced. Since most of the other bits of information in this context could meanwhile be proven and references provided, these two remaining unsourced bits of information were restored as footnote now on the principle of assuming good faith. Still, it is desirable to have a reliable reference for this. If you find one, please add it. Also see talk.}}</ref>

}}

==References==