Abstract: A breathing mask for aircraft crewmember comprising an on-demand regulator, said regulator comprising an inlet connected to a source of breathing gas and an outlet to exhaust the breathing gas, said outlet having an aperture controlled by a movable valve (18) having an open position when the crewmember breathes out and a closed position when the crewmember breathes in, wherein said breathing mask comprises latch means (30) operable by said crewmember to latch said valve in the open position, said latch means comprising an unlocking means (42, 46, 48) to release said valve when the cabin pressure is below a predetermined value.