Air corridor

An Air Corridor was a type of corridor that could be used to supply and dispell air through a chosen part of unprotected and non oxygenated segment of space. The Doctor's Tardis had the ability to create an air corridor, and did so for River Song's escape of the Byzantium ship for her to reach the TARDIS safely. (DW: The Time of Angels).

The same mechanism was used in The Beast Below, to create the bubble of air, around the TARDIS for Amy when she was outside the TARDIS in the opening scene.