Passage: The airline was established on 20 September 1991 and began operations on 3 December 1993 with two Boeing 737-200 aircraft as Sahara Airlines, as part of the major Sahara India Pariwar business conglomerate. Initially services were primarily concentrated in the northern sectors of India, keeping Delhi as its base, and then operations were extended to cover all the country. Sahara Airlines was rebranded as Air Sahara on 2 October 2000, although Sahara Airlines remains the carrier's registered name. On 22 March 2004 it became an international carrier with the start of flights from Chennai to Colombo, later expanding to London, Singapore, Maldives and Kathmandu. It had also planned to become the first private Indian carrier to serve China with flights to Guangzhou from winter 2006, however this did not materialize. The uncertainty over the airline's fate caused its share of the domestic Indian air transport market go down from approximately 11% in January 2006 to a reported 8.5% in April 2007.

Question: What year was the airline established?
1991