New Delhi:

The Delhi Flying Club, established in 1928 with two de Havilland Moth aircraft named Delhi and Roshanara, was based at Safdarjung Airport which started operations in 1929, when it was the Delhi's only airport and the second in India. The airport functioned until 2001, however in January 2002 the government closed the airport for flying activities because of security concerns following the New York attacks in September 2001. Since then, the club only carries out aircraft maintenance courses, and is used for helicopter rides to Indira Gandhi International Airport for VIP including the president and the prime minister.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". In what year did the government close Safdarjung Airport due to security concerns?
2002