The plane crashed around 20.10 Moscow time 50 km from the town of Feodosia. The military detected a signal from the aircraft's emergency beacon prior to the crash.
Search and rescue operations commenced immediately - an An-26 plane, a Mi-8 helicopter and a small anti-submarine vessel are taking part in the effort.
This is the second recorded Russian military plane crash of the day - an L-39 combat training plane flown by a cadet crashed in a field in the Krasnodar region on the afternoon of March 25. According to a report by the Interfax News Agency, the pilot was killed, with technical failure cited as a preliminary cause of the crash.
The Su-27 is a fourth-generation multirole fighter. The plane officially entered service with the Soviet Air Forces in 1985, and is one of the Russian Air Force’s main aircraft.