A B727-200 IN CRUISE AT FL330 DECLARED AN EMER AND DSNDED DUE TO LOSS OF CABIN PRESSURE CAUSED BY THE #3 ENG BLEED TRIP AND SLIGHT HULL LEAKAGE.

Narrative

WHILE AT CRUISE ALT FL330; THE CABIN BEGAN AN UNSCHEDULED CLB AT 1500 FPM. COCKPIT CREW WENT IMMEDIATELY ON OXYGEN. AS FE CONSULTED APPROPRIATE CHKLIST IN MANUAL; I REQUESTED A LOWER ALT FROM ATC AND DECLARED AN EMER. ATC SAID WE CAN HAVE LOWER BUT MUST FIRST TURN 40 DEGS TO THE L. THE FO MADE THE TURN AND THEN BEGAN A NORMAL DSCNT. ATC ASKED US TO MAINTAIN ALT FOR OPPOSITE DIRECTION TFC. BY THIS TIME; THE FE HAD THE CABIN PRESSURE UNDER CTL. AFTER DSNDING 500 FT; THE FO BEGAN CLBING BACK TO FLT LEVEL AT WHICH TIME ATC CLRED US TO FL250. WE CONTINUOUSLY MONITORED THE OPPOSITE DIRECTION TFC ON TCASII. SAFETY WAS NEVER IN QUESTION. THE CAUSE FOR THE LOSS OF CABIN PRESSURE WAS A BLEED VALVE TRIP ON THE #3 ENG. THE HIGHEST CABIN ALT DURING THIS TIME WAS 8000 FT MSL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE ACFT WAS A B727-200 AND THE CAUSE OF THE LOSS OF PRESSURE WAS A COMBINATION OF THE #3 ENG BLEED TRIPPING OFF; MINOR HULL LEAKAGE THROUGH THE CARGO DOOR SEALS AND ONE PACK OP. THE RPTR SAID THE CABIN ALT INCREASED VERY SLOWLY AND NEVER EXCEEDED 8000 FT AND WHEN THE ACFT DSNDED TO FL250 THE CABIN PRESSURE WAS NORMAL. THE RPTR SAID NO INFO WAS AVAILABLE FROM MAINT ON THE CORRECTIVE MAINT ACTION TAKEN.