About this issue
Hungary's first airmail stamps appeared on 4 July 1918 for the air post from Budapest to Vienna and on to Kraków and Lviv: two Parliament stamps of 1916 were overprinted REPÜLŐ POSTA with new values of 1 K 50 f and 4 K 50 f. The air fee was 1 K 50 f per stage – once to Vienna, twice to Kraków, three times to Lviv – plus a 1-korona handling fee and 60 fillér for express. They were sold only until 24 July 1918, with 70,000 of each printed; the Vienna–Budapest line flew twice a day, but complications and accidents ended it after a few weeks.
Sources: Wikikönyvek: 1918. évi magyar bélyegek, Hungarian Stamps: Parliament Issues, Austria-Forum: 100 Jahre Flugpost