Narrative:

While at cruise altitude FL330, the cabin began an unscheduled climb at 1500 FPM. Cockpit crew went immediately on oxygen. As flight engineer consulted appropriate checklist in manual, I requested a lower altitude from ATC and declared an emergency. ATC said we can have lower but must first turn 40 degrees to the left. The first officer made the turn and then began a normal descent. ATC asked us to maintain altitude for opposite direction traffic. By this time, the flight engineer had the cabin pressure under control. After descending 500 ft, the first officer began climbing back to flight level at which time ATC cleared us to FL250. We continuously monitored the opposite direction traffic on TCASII. Safety was never in question. The cause for the loss of cabin pressure was a bleed valve trip on the #3 engine. The highest cabin altitude during this time was 8000 ft MSL. Callback conversation with reporter revealed the following information: the reporter stated the aircraft was a B727-200 and the cause of the loss of pressure was a combination of the #3 engine bleed tripping off, minor hull leakage through the cargo door seals and one pack operation. The reporter said the cabin altitude increased very slowly and never exceeded 8000 ft and when the aircraft descended to FL250 the cabin pressure was normal. The reporter said no information was available from maintenance on the corrective maintenance action taken.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.