Narrative:

Departed with left pack deferred due temperature controller issues (did we really need to lose entire pack for that problem? I think maintenance manual did not put much thought into that; especially as maintenance control after satcom discussion sent note to printer asking same question). We were restr to FL340 maximum; and about 20 mins after leveloff; the cabin altitude warning went off. Both pilots immediately donned O2 masks; but although I confirmed and reconfirmed switchology; we were not able to talk to each other with masks on. I attempted to run qrc but captain could not hear me; and he; therefore; wisely declared emergency with ATC seeking lower altitude. (I could hear his xmissions; but my speaker was very crackly.) he began emergency descent while I continued checking items on qrc for firstly cabin altitude; then emergency descent. I was communicating mostly using semaphore and; therefore; it was obvious that the sooner we could get masks off the better. We elected to turn deferred pack back on using our emergency authority/authorized. The left pack immediately caught the cabin; and the cabin altitude descended quickly below 10000 ft; at which point I removed my mask and told the captain he could do same. He continued descent and we both worked on clean-up items; such as communicating with the passenger and flight attendants. I computed distance/fuel flow issues and we discussed our options and decided it was not an issue to continue to ZZZ with perfect VFR WX and a planned landing fuel of about 55 mins endurance remaining at 10000 ft holding speed. I talked with dispatch and maintenance on satcom and all parties were comfortable with continuing. I canceled emergency and we continued to ZZZ with no further issues. Editorial unresolved questions/concerns: why single pack did not hold (we checked it several times in climb and initial leveloff; a creeper for sure). This will make me think hard before accepting an aircraft with single pack operation in future. I was surprised that MEL let us fly so high; when other aircraft are restr to FL250. Why pack was deferred; especially as maintenance had same concern during satcom conference: I think maintenance was in too big a rush to defer without really thinking this through. (Benefit of hindsight; etc.) why we operate with interior intracockpit communications on this fleet. Can we not get better masks and mikes/speakers? ATC had great difficulty understanding us; as well as our own communications problems. A full face mask would have been of great help (I lost my glasses initially putting mask on). And now the high points: great CRM and overall leadership by the captain. Great and immediate help from dispatch and maintenance and ATC.

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Original NASA ASRS Text

Title: B767-300 IS DISPATCHED WITH ONE PACK INOP. AFTER LEVELOFF; CABIN ALT WARNING ACTIVATED AND FLT CREW INITIATED EMER DESCENT.

Narrative: DEPARTED WITH L PACK DEFERRED DUE TEMP CONTROLLER ISSUES (DID WE REALLY NEED TO LOSE ENTIRE PACK FOR THAT PROB? I THINK MAINT MANUAL DID NOT PUT MUCH THOUGHT INTO THAT; ESPECIALLY AS MAINT CTL AFTER SATCOM DISCUSSION SENT NOTE TO PRINTER ASKING SAME QUESTION). WE WERE RESTR TO FL340 MAX; AND ABOUT 20 MINS AFTER LEVELOFF; THE CABIN ALT WARNING WENT OFF. BOTH PLTS IMMEDIATELY DONNED O2 MASKS; BUT ALTHOUGH I CONFIRMED AND RECONFIRMED SWITCHOLOGY; WE WERE NOT ABLE TO TALK TO EACH OTHER WITH MASKS ON. I ATTEMPTED TO RUN QRC BUT CAPT COULD NOT HEAR ME; AND HE; THEREFORE; WISELY DECLARED EMER WITH ATC SEEKING LOWER ALT. (I COULD HEAR HIS XMISSIONS; BUT MY SPEAKER WAS VERY CRACKLY.) HE BEGAN EMER DSCNT WHILE I CONTINUED CHKING ITEMS ON QRC FOR FIRSTLY CABIN ALT; THEN EMER DSCNT. I WAS COMMUNICATING MOSTLY USING SEMAPHORE AND; THEREFORE; IT WAS OBVIOUS THAT THE SOONER WE COULD GET MASKS OFF THE BETTER. WE ELECTED TO TURN DEFERRED PACK BACK ON USING OUR EMER AUTH. THE L PACK IMMEDIATELY CAUGHT THE CABIN; AND THE CABIN ALT DSNDED QUICKLY BELOW 10000 FT; AT WHICH POINT I REMOVED MY MASK AND TOLD THE CAPT HE COULD DO SAME. HE CONTINUED DSCNT AND WE BOTH WORKED ON CLEAN-UP ITEMS; SUCH AS COMMUNICATING WITH THE PAX AND FLT ATTENDANTS. I COMPUTED DISTANCE/FUEL FLOW ISSUES AND WE DISCUSSED OUR OPTIONS AND DECIDED IT WAS NOT AN ISSUE TO CONTINUE TO ZZZ WITH PERFECT VFR WX AND A PLANNED LNDG FUEL OF ABOUT 55 MINS ENDURANCE REMAINING AT 10000 FT HOLDING SPD. I TALKED WITH DISPATCH AND MAINT ON SATCOM AND ALL PARTIES WERE COMFORTABLE WITH CONTINUING. I CANCELED EMER AND WE CONTINUED TO ZZZ WITH NO FURTHER ISSUES. EDITORIAL UNRESOLVED QUESTIONS/CONCERNS: WHY SINGLE PACK DID NOT HOLD (WE CHKED IT SEVERAL TIMES IN CLB AND INITIAL LEVELOFF; A CREEPER FOR SURE). THIS WILL MAKE ME THINK HARD BEFORE ACCEPTING AN ACFT WITH SINGLE PACK OP IN FUTURE. I WAS SURPRISED THAT MEL LET US FLY SO HIGH; WHEN OTHER ACFT ARE RESTR TO FL250. WHY PACK WAS DEFERRED; ESPECIALLY AS MAINT HAD SAME CONCERN DURING SATCOM CONFERENCE: I THINK MAINT WAS IN TOO BIG A RUSH TO DEFER WITHOUT REALLY THINKING THIS THROUGH. (BENEFIT OF HINDSIGHT; ETC.) WHY WE OPERATE WITH INTERIOR INTRACOCKPIT COMS ON THIS FLEET. CAN WE NOT GET BETTER MASKS AND MIKES/SPEAKERS? ATC HAD GREAT DIFFICULTY UNDERSTANDING US; AS WELL AS OUR OWN COMS PROBS. A FULL FACE MASK WOULD HAVE BEEN OF GREAT HELP (I LOST MY GLASSES INITIALLY PUTTING MASK ON). AND NOW THE HIGH POINTS: GREAT CRM AND OVERALL LEADERSHIP BY THE CAPT. GREAT AND IMMEDIATE HELP FROM DISPATCH AND MAINT AND ATC.

Data retrieved from NASA's ASRS site as of January 2009 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.