A Rossiya Boeing 737-800 on behalf of Aeroflot, registration VQ-BJX performing flight SU-6551 from Moscow Vnukovo to Sochi (Russia) with 157 people on board, was climbing through FL145 out of Moscow when the crew rapidly descended the aircraft due to a cabin pressure warning. The aircraft entered a hold at FL070, then landed back at Vnukovo Airport about 45 minutes after departure. A replacement Boeing 737-800 registration VQ-BPX reached Sochi with a delay of 4 hours. On Apr 12th 2017 Rosaviatsia reported the cabin did not pressurize due to incorrect closure of the cabin door which left a gap between door and door opening. A malfunction in the door mechanics contributed. Rosaviatsia issued seven recommendations to the operator to be implemented by Apr 30th 2017 (editorial comment: Rosaviatsia actually wrote Apr 31st 2017).