Det är en rysk stad eller flygplatsidentifierare. Många små städer har inte IATA-koder, men har interna ryska koder.
Detta system kallas CRT (Centrum för scheman och tariffer, ЦРТ, Центр Расписаний и Тарифов) uppkallad efter en avdelning i organisationen som förvaltar dem (se nedan). Wikipedia artikeln citerade nedan hävdar att det också kallas "Sirena" -koden (uppkallad efter Sirena - ett bokningssystem för flyg- och järnvägsbiljetter).
Här är en översättning av ett fragment från Ryska Wikipedia :
The internal city and airport coding system in the former USSR is structured analogous to IATA. [...]
The airport code in this system consists of 3 letters of the Russian alphabet. As in IATA codes, the 3-letter combination is interpreted as atomic and has no internal structure. As in case with IATA, all 3-letter codes are unique.
Like IATA, the codes were assigned to cities such that the code has something in common either with the name of the city or with its IATA code [...] Contrary to IATA, the internal codes were changed after cities were renamed in the 1990s: Saint Petersburg's internal code was changed from ЛЕД to СПТ, Samara (formerly Kuibyshev) -- from КУФ to СМШ, Ekaterinburg (formerly Sverdlovsk) -- from СВХ to ЕКБ.
Many small cities and airports in the former USSR have an internal code only.
In late 1990s foreign (non-Russian) cities were assigned internal codes because of the popularity of these destinations (e. g. Barcelona -- БЦН).
As of April 2009, there are about three thousand internal codes that are actively used.
Det verkar som att koderna bibehålls av Transporthanteringshuset . Sektionen Kodningskataloger på deras sida Schema & Tariffer säger:
STC maintains the aggregated database of coding directories for the purpose of universal use of codes in information systems for passenger services reservation and sales, publication of timetables and fares, ticketing, settlement and other commercial issues related to passenger services.
STC maintains the codifiers in pursuance of Provision on Assignment, Maintenance and Use of Internal Codes of Carriers, Organizations, Airports, Cities (points) and Civil Aviation Agencies (№ ДВ-63/и dated 12.05.94) and Directive "On Coding Directories Approval” (№ ДВ-109/и date 14.07.94).
STC supports the following coding directories:
Airlines Airports Cities
På ryska är STC översatt som CRT (ЦРТ) och jag har hört att folk hänvisar till de interna koderna som "CRT-koder".