Soviet Union. July 25-27, 1931, North Pole Zeppelin Flight registered cover from Leningrad to Ice-Breaker ''Malygin'', franked by perforated complete set of four, tied by Leningrad ''25.VII.31'' special ds, German confirmation cachet, arrival ''27.VII.31'' and all appropriate markings, mostly VF, Sieger #120Ca, €1,300, Est. $600-$800 (Image)

Soviet Union. September 12-16, 1932, 6th SAF postcard from Moscow to Pernambuco, franked by three airship stamps, Berlin connection, green confirmation cachet, Pernambuco ''16.X.32'' arrival ds is alongside, VF, Sieger #177, Est. $450-$500 (Image)

Soviet Union. August 5-8, 1933, 4th South America Flight registered cover from Leningrad to Brazil, franked by four stamps, including three Zeppelin adhesives, delivered by flight Leningrad - Berlin with connecting ''29.7.33'' ds, two confirmation markings and Pernambuco ''8.VIII.33'' arrival hs, slight traces of mounts on reverse, still VF and scarce, Est. $450-$500 (Image)

Soviet Union. September 1-5, 1934, 7th SAF registered cover from Zaporizhia via Moscow and Berlin to Brazil, franked by high value of definitive set - worker 5r blue and brown on watermarked paper, Berlin and Friedrichshafen connections and flight confirmation cachet are alongside, postmarked at Pernambuco ''5.IX.34'', VF, unusual origin and very rare franking making this item completely outstanding, Est. $500-$750 (Image)