There are reports that Belbek airport has been surrounded by an unknown militia.
Although civilian flights were suspended in 2007, the airfield, currently guarded by unknown troops is known as Sevastapol International airport.
Its current occupants are the Ukranian Department of Defence and specifically the 204th Tactical Aviation Brigade of the Ukrainian Air Force, equipped with the Mig-29 Fulcrum.
The airfield itself is a few kilometers north of the strategically important port of Sevastapol and has a 3,009 mt (9,863 ft) long runway which can also handle any weight aircraft (indeed, it is described as unlimited maximum take off weight).
Perfect for heavily laden transport aircraft needed to supply a potential air bridge between the Russian Black Sea fleet and Russia itself.
Two videos have already surfaced showing 12 Russian helicopters entering the airspace over Crimea.
There are also reports that Russian jets are flying combat air patrol (CAP) over the Sea of Azov to the east of the Crimean Peninsula right up to Ukrainian airspace; the airspace over Savastopol is closed.
Image credit: Google Earth (top) and FlightRadar24.