Air Mail cover 1918 (10 July) Budapest-Vienna-Lemberg flight, registered envelope bearing Air 4K.50f. together with two other adhesives cancelled by "BUDAPEST/4" c.d.s., reverse showing Vienna (10.7) and Lemberg (11.7) "FLUGPOST" c.d.s., together with "ETAPPENPOSTAMT" arrival c.d.s. (13.7). Rare. Photo