A Boeing 737-800 belonging to Yakutia, with registration VQ-BOY, was performing a flight from Krasnodar to Istanbul. The plane was climbing to flight level 180 when the crew noticed the air conditioning systems are inoperative. The cabin pressure dropped significantly and the cockpit crew immediately descended to flight level 100. They returned to the airport safely.
Rosaviatsia reported an alarm activated that the aircraft was climbing without airconditioning.