Absolute airmail rarity. The 10Pf flight stamp for the Regensburger Flugtage in very rare freshly colored best condition with flight stamp "Erste Regensburger Flugtage" genuinely transported with the special postal stationery of the Bavarian Aero Clubs. Hard to find again in this combination and quality. The flight stamps were only printed in a mini edition on glossy paper and are hard to come by. Cataloged in the Michel under "semi-official flight stamps".