Russia 1928 (May 9) Soviet Union, USSR  Registered Air Mail Cover Moscow to Riga, Latvia. Cover showing Airmail label and cachet, bearing two sets of the Aircraft ANT-3 Over World Map set of 2 values 15k & 10k (Mi:326-327; Scott C10-C11; Yt: PA18 -19; SG. 499-500),  Deruluft air mail cachet and arrival Riga 10.5.28.