Off-nominal situation leading to the loss of Proton-M booster with Mexican MexSat-1 satellite happened at 08.59, Moscow time, May 16, 2015 one minute before the space device and the upper stage were t o separate from the 3rd stage of the booster. According to preliminary data the accident was caused by Proton 3rd stage steering engine failure.
Short after the accident Roscosmos Head Igor Komarov ordered to form State Commission to investigate the cause of the accident.