1928 (13 Sep) Austria Vienna - Berlin - Moscow - Baku then back to the sender, Expres Airmail Registered cover, flights Vienna - Berlin, Berlin - Moscow, Moscow - Baku (Muller 147 (Austria), 353 (Germany), 26 (USSR) CV $2,850)

From ex Dr. Peter Moeller collection that received the Large Gold Medal at the Hannover 2011 Exhibition.

Vienna - Berlin - Moscow -
Baku/Azerbaijan

As of 13.9.1928 airmail delivery with express flight Vienna - Berlin to the Deruluft connection Berlin - Moscow with connecting flight Moscow - Baku

Postmark:
Vienna 13.9.1928
Berlin MLb
Moscow 16.9.1928
Moscow MLb
Baku 19.9.1928

Postage:
Letter abroad 0,40 ÖS
Lp surcharge 1,20 ÖS
Registered mail 0,60 ÖS
Total 2,20 ÖS postage due

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Wien - Berlin - Moskau -
Baku/Aserbeidschan

Ab 13.9.1928 Luftpostzuleitung mit Eilflug Wien - Berlin zur Deruluft-Verbindung Berlin - Moskau mit Anschlussflug Moskau - Baku

Poststempel:
Wien 13.9.1928
Berlin MLb
Moskau 16.9.1928
Moskau MLb
Baku 19.9.1928

Porto:
Brief Ausland 0,40 ÖS
Lp-Zuschlag 1,20 ÖS
Einschreiben 0,60 ÖS
Total 2,20 ÖS portogerecht