On December 20, 1931 the Eurasia Aviation Corporation(歐亞航空公司) made trial flights to the Northwest from Peiping to Tihwa (迪化) stopping on the way Kweihwa (歸化) and Rosueiher (弱水河). During the trial period ordinary postage rates were permitted for air mail. But beginning on August 11 of the same year, air mail postage was collected in accordance with postal regulations. Because of the difficulty which Sinkiang had experienced in getting a reasonable quantity of air mail stamps from the Postal Supply Department of the Directorate General of Posts, the Sinkiang District Head Office was authorized to convert a number of the Reaper definitive stamps (30￠denomination of the 1st Peking Print and 15￠denomination of the 2nd Print) as air mail stamps by over-printing with the Regular-Writing characters〝航空〞(aviation) on both sides of the wording 〝限新省貼用〞(restricted for use in Sinkiang) previously overprinted in black color in a vertical line on the stamps. The overprint was done with a wood hand chop on the stamps. During the trial period the flights were irregular. Regular service started from the middle of December 1932. On June 8, 1933, when the air mail postage was revised, 5￠and 10￠denominations of Junk definitive stamps of the 2nd Peking Print originally bearing the overprint 〝限新省貼用〞(restricted for use in Sinkiang) were similarly overprinted to match the sale.