BEIJING -- A Soviet-built Chinese airliner that exploded Monday killing all 160 people on board had not been overhauled since 1992 but had been serviced for "malfunctions" only three days before, the airline said. In the first detailed account of China's worst civil air disaster, China Northwest Airlines general manager Gao Junyue said the crash was the "first time in Chinese aviation history that a passenger plane had blown up in mid-air." Gao, quoted in Thursday's official China Daily, said the Soviet-built Tupolev-154 "was reported to have some malfunctions" on June 3. He did not describe the problems. "It was soon repaired and was determined in test flying to be satisfactory," China Daily quoted Gao as saying. "Monday's fatal trip was its first formal flight since then." Gao said the plane, procured from an unnamed Russian firm, had flown about 10,000 hours --about a third of its expected life -- but had not been overhauled since 1992 and had flown 2,857 hours since then. Gao quoted the Russian manufacturer as saying the Tu-154 was considered "new" at an age of 10,000 flying hours. He said the maker agreed with China's request to send investigators. Analysts said the Russian plane's apparently questionable airworthiness was likely to raise serious new questions about China's willingness to use surplus Soviet-era aircraft to cope with a staggering 20 percent annual growth of its aviation market. Only hours before the crash, which killed all passengers and 14 crew, Beijing had trumpeted its lease of five more surplus Tu-154s from the former Soviet republics. Gao "ruled out a quick explanation" of what caused the plane to blow up eight minutes after taking off from Xian on a scheduled route to Guangzhou, saying investigators were still analyzing the plane's cockpit data recorder. But he did say it was clear that the pilot could not control the aircraft, which then exploded and splintered into three pieces.