Isobaric range

The range of cabin pressurization in which cabin pressure is maintained at a constant level (a constant cabin altitude), rather than allowing it to change with flight altitude. Most cabin pressurization systems operate in the isobaric range up to the altitude at which the cabin differential pressure is the maximum allowed by the aircraft structure. Then the system automatically shifts to the constant-differential mode, which keeps a constant pressure difference between the pressure of the air inside the cabin and the air outside the cabin.