Airmail, 1930, $1.30 + $2.60 Graf Zeppelins. $2.60 plate no. single, both tied by Washington D.C. duplex postmark on South American Round Trip flight cover, flight cachets including round trip handstamp, Friedrichshafen and New York backstamps, Very Fine and choice. Scott No. C14-C15  Estimate $500 - 750. $0 (Image)