Pioneer airmail card flown on the Gelber Hund (Yellow Dog) mail plane with called-for Rhein Main semi-official Flugpost / Airmail Goose issue overprinted 'Gelber Hund'. A bit worn, as per scan. Nice usage; this bears the Nr 835 handstamp and message reverse "Diese Karte fleigt unter dem Protektorat der Grossherzogin" / "This card flown under the auspices of the Grand Duchess" (Sieger Vi variant), '01 CV EUR620