Dear,
Thasnk you very much for discussing politely. Please send me e-mail, to [email protected], and I will reply more extensively. Also I can then get help from a Russian person, I have been talking to him quite much and he will surely be able to explain better than I can.
Kind regards from Belgium,
Karel ADAMS
(and my apologies for not writing in your languate - I am told it is beautiful but hard to learn because there are many rules and many exceptions to all those rules :) )

Sorry I do not agree. ICAO codes for the former Soviet Union begin with U. You can refer to https://en.wikipedia.org/wiki/List_of_airports_by_ICAO_code:_U andd to many other references. Codes not Uxxx in Russia/CIS are non-ICAO. I discussed this with map.aopa.ru before changing! Regards,