Two Thai Air Force pilots were killed on Thursday when their aircraft crashed outside the northern city of Chiang Mai during a training mission, the military said.The AT-6TH Wolverine light attack and reconnaissance plane went down in Chom Thong district, about 60 kilometres from Chiang Mai airport, in a military training area, spokesperson Air Marshal Jackkrit Thammavichai said.The cause of the crash of the two-seater turboprop aircraft is under investigation.Thailand recently acquired the fighter-trainer, which is produced in the United States by Beechcraft, a part of Textron Aviation. The Thai Air Force commissioned the final of its eight AT-6TH planes in September.