What was found
THE CABIN ALTITUDE WAS NOTED AS UNUSUALLY HIGH. THE CABIN RATE CONTINUED TO CLIMB AS THE AIRCRAFT DESCENDED AND THE CABIN ALTITUDE WARNING HORN SOUNDED. THE CREW DECLARED AN EMERGENCY AND PERFORMED AN EMERGENCY DESCENT WHILE DONNING THE OXYGEN MASKS. THE AIRCRAFT LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE ISSUED MEL 21-30-5 FOR THE OUTFLOW VALVES AND THE AIRCRAFT WAS RETURNED TO SERVICE. ON AUGUST 22, 2005 A PRESSURIZATION SYSTEM FUNCTIONAL TEST WAS PERFORMED BY MAINTENANCE. SYSTEM OPERATION WAS SATISFACTORY. THE CABIN OXYGEN MASKS WERE CLEANED AND STOWED AND A SATISFACTORY CHECK FLIGHT WAS PERFORMED. THE AIRCRAFT WAS RETURNED TO SERVICE.