Abstract: An aircraft pneumatic cabin pressure control system that is adapted to prevent the difference between cabin pressure and atmospheric pressure from exceeding a threshold value wherein the threshold value varies in relation to aircraft altitude. In some instances the control system includes at least one outflow valve adapted to prevent the difference between cabin pressure and atmospheric pressure from exceeding a threshold value, and the control system is adapted to override the outflow valve at predetermined altitudes. The control system may implement a method for controlling the cabin pressure of an aircraft using a pneumatic cabin pressure control system that includes an outflow valve comprising at least two pressure input ports, the method comprising coupling an isolation valve to an input port of the outflow control valve and utilizing the interrupt valve to isolate the outflow valve input port to which the isolation valve is coupled from pressure changes.