![WZ-9 helicopters fly at night(3/6)](http://www.ecns.cn/hd/2017/04/19/0bc8de0164c1427c8d6eb2d3b038b026.jpg)
A WZ-9 helicopter attached to a helicopter group of the PLA Air Force Xi'an Flight College takes off for a sortie during a night flight training exercise at a military training base in southwest China's Sichuan Province in mid-March, 2017. (Photo/81.cn)