Russian investigators looking into the crash of a military plane that killed all 92 on-board, believe a fault with its wing flaps was the reason it plunged into the Black Sea.<br/><br/>The plane, a Tupolev-154 belonging to the Defence Ministry, disappeared from radar screens two minutes after taking off on Sunday from Sochi in southern Russia en route to Syria.<br/><br/>Russian news agencies said, three black box flight recorders from the aircraft were found yesterday. <br/><br/>The Interfax news agency cited an unnamed investigative source as saying preliminary data showed the wing flaps had failed and not worked in tandem.