Patent ID: 7784462

Claim:
An oxygen supply system for a passenger aircraft, said system comprising at least one therapeutic oxygen breathing mask (OM) accessible to passengers, an emergency oxygen supply first subsystem (EOS) including a first oxygen source ( 1 ), a therapeutic oxygen supply second subsystem (TOS) including a second oxygen source ( 1 ′, 22 ), a first oxygen conduit (EOC) connecting said first oxygen source ( 1 ) to said at least one therapeutic oxygen breathing mask (OM), a second oxygen conduit (TOC) connecting said second oxygen source ( 1 ′, 22 ) to said at least one therapeutic oxygen breathing mask (OM), controllable valve means in at least one of said first and second oxygen conduits (EOC, TOC) for connecting said at least one therapeutic oxygen breathing mask selectively to one of said first subsystem (EOS) and said second subsystem (TOS), a control ( 16 , 26 ) connected to said second subsystem (TOS) for activating said second subsystem (TOS), whereby said at least one therapeutic oxygen breathing mask is selectively usable in said first subsystem and in said second subsystem, wherein said controllable valve means comprises pressure responsive valves ( 9 , 10 ) for switching between said first subsystem (EOS) and said second subsystem (TOS) so that oxygen is supplied to said at least one therapeutic oxygen breathing mask (OM) from said first oxygen source ( 1 ) when a cabin pressure in said passenger aircraft falls below a predetermined cabin pressure threshold value, and so that oxygen is supplied to said at least one therapeutic oxygen breathing mask (OM) from said second oxygen source ( 1 ′, 22 ) when said cabin pressure rises above said predetermined cabin pressure threshold value.