Gillham code: Difference between revisions

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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.<!-- while having a family dinner. --><!-- Reportedly he "suddenly" died in March 1968. --> The final code variant was developed in late 1961 for the ICAO VIICommunications COMDivision meeting (VII COM) held in January/February 1962.<ref name="IEEE_1983"/> The exact timeframe and circumstances of the term ''Gillham code'' being coined are unclear, but by 1962<!-- 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_1962"/><ref name="CE_1963"/> and described in an [[FAA]] report.<ref name="FAA_1962"/><ref name="FAA_1962_T6"/><ref name="FI_1964"/> 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.