The aircraft emergency oxygen supply system includes one or more sources of supplemental breathable oxygen, one or more inlet valves for one or more breathing devices, connected to the inlet valves, and one or more cabin air pressure transducers. A pressure controller controls the inlet valves in response to the one or more cabin air pressure transducers. One or more second pressure transducers may connected to conduits downstream of inlet valves to be monitored, and the pressure controller may also control operation of the inlet valves in response to the one or more second pressure transducers.