Aircraft pressurization systems operate automatically, but crews must confirm correct operation by monitoring cabin altitude, cabin rate of climb and descent, and differential pressure. The safety valve acts to prevent cabin pressure from exceeding the maximum, allows air into the cabin when ambient pressure exceeds cabin pressure, and as a dump valve for the flight crew to dump cabin air manually. A cabin altimeter, differential pressure gauge, and cabin rate of climb gauge help the crew to monitor the aircraft pressurization. Oxygen masks will drop in the cabin automatically when the cabin altitude reaches 14,000 feet, according to information at Airbus. Cabin crew should grab the nearest mask and secure themselves until the flight crew says that it is safe to move.