New Delhi: Thirty-one aircraft of the Indian Air Force have been involved in accidents in the last four years, the government informed the Lok Sabha on Wednesday. In a written reply to a question, Minister of State for Defence Subhash Bhamre said 10 accidents had taken place in 2014-15 while the number was six in 2015-16 and 10 in 2016-17. The number of accidents reported in 2017-18 was five. "Every aircraft accident in the Indian Air Force is investigated by a Court of Inquiry (CoI) to ascertain the cause of accident," Bhamre said. He said phasing out of the aircraft and their replacement with new generation aircraft depends upon national security, strategic objectives and operational requirements of the defence forces.