Bidspirit auction | Worldwide Air Post Stamps and

Worldwide Air Post Stamps and Postal History - Soviet Union - 1927 (September 27), Pioneer Flight registered cover from Moscow to Riga, franked by 4 stamps of the Hague Air Post Conference, one 10k with broken undercarriage variety, backstamped Moscow-Exp. date stamp, minor reversal foxing, mostly VF, Scott #C10-11