Narrative:

We returned to the gate at slc due to a problem with our right airconditioner. The problem could not be corrected, so we were dispatched with the right airconditioner inoperative. This MEL condition restr our maximum flight altitude to FL350. After takeoff, we climbed to and leveled off at FL330. During climb out, cabin pressurization was checked often and appeared normal. After several mins at cruise altitude, we received the 'cabin altitude' warning. The pressurization control panel showed a cabin altitude of 10000 ft with a cabin rate of climb of 200-300 FPM. The outflow valve showed closed. We donned our oxygen masks and requested an immediate descent. After declaring an emergency with ATC, we were cleared to FL240 (or thereabouts). The power reduction required for descent caused the cabin to climb at 1000 FPM. We continued our descent to FL240. The cabin altitude was now at approximately 1200 ft and climbing. We declared an emergency several more times requesting a descent to MEA and squawked 7700 with the transponder. The controller didn't realize the time critical nature of our descent and said he would give us a lower altitude after passing traffic. We emphasized that we were an emergency aircraft and needed further descent. Further descent was granted after ATC turned another aircraft. We descended to 16000 ft, and we received a clearance to slc. Cabin pressurization was recovered and cabin altitude began to descend somewhere between FL240 and 16000 ft. Passenger oxygen mask did not deploy as the cabin did not get above 14000 ft. On the return to slc, we received a 'cabin altitude automatic 1' status message. Several mins later we received a 'left pack temperature' EICAS message and a left pack 'inoperative' light on the air- conditioning panel. An uneventful return to slc airport was accomplished. All necessary checklists were accomplished at the appropriate time. No passenger or crew members were hurt. Callback conversation with reporter revealed the following information: the reporter flies the B-757 and does not know what caused the pressurization problem. He knows that several 'black boxes' were changed. He believes that he took off 'with the better pack' disabled per MEL. His air carrier's FAA liaison talked directly with the ARTCC controller that denied the lower altitude. The controller 'had a plan' for giving a lower altitude after traffic passed. The reporter's trip was canceled and he has not flown this aircraft since the day of the incident.

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Original NASA ASRS Text

Title: EMER DSCNT FOLLOWING A GRADUAL LOSS OF PRESSURIZATION.

Narrative: WE RETURNED TO THE GATE AT SLC DUE TO A PROB WITH OUR R AIRCONDITIONER. THE PROB COULD NOT BE CORRECTED, SO WE WERE DISPATCHED WITH THE R AIRCONDITIONER INOP. THIS MEL CONDITION RESTR OUR MAX FLT ALT TO FL350. AFTER TKOF, WE CLBED TO AND LEVELED OFF AT FL330. DURING CLBOUT, CABIN PRESSURIZATION WAS CHKED OFTEN AND APPEARED NORMAL. AFTER SEVERAL MINS AT CRUISE ALT, WE RECEIVED THE 'CABIN ALT' WARNING. THE PRESSURIZATION CTL PANEL SHOWED A CABIN ALT OF 10000 FT WITH A CABIN RATE OF CLB OF 200-300 FPM. THE OUTFLOW VALVE SHOWED CLOSED. WE DONNED OUR OXYGEN MASKS AND REQUESTED AN IMMEDIATE DSCNT. AFTER DECLARING AN EMER WITH ATC, WE WERE CLRED TO FL240 (OR THEREABOUTS). THE PWR REDUCTION REQUIRED FOR DSCNT CAUSED THE CABIN TO CLB AT 1000 FPM. WE CONTINUED OUR DSCNT TO FL240. THE CABIN ALT WAS NOW AT APPROX 1200 FT AND CLBING. WE DECLARED AN EMER SEVERAL MORE TIMES REQUESTING A DSCNT TO MEA AND SQUAWKED 7700 WITH THE XPONDER. THE CTLR DIDN'T REALIZE THE TIME CRITICAL NATURE OF OUR DSCNT AND SAID HE WOULD GIVE US A LOWER ALT AFTER PASSING TFC. WE EMPHASIZED THAT WE WERE AN EMER ACFT AND NEEDED FURTHER DSCNT. FURTHER DSCNT WAS GRANTED AFTER ATC TURNED ANOTHER ACFT. WE DSNDED TO 16000 FT, AND WE RECEIVED A CLRNC TO SLC. CABIN PRESSURIZATION WAS RECOVERED AND CABIN ALT BEGAN TO DSND SOMEWHERE BTWN FL240 AND 16000 FT. PAX OXYGEN MASK DID NOT DEPLOY AS THE CABIN DID NOT GET ABOVE 14000 FT. ON THE RETURN TO SLC, WE RECEIVED A 'CABIN ALT AUTO 1' STATUS MESSAGE. SEVERAL MINS LATER WE RECEIVED A 'L PACK TEMP' EICAS MESSAGE AND A L PACK 'INOP' LIGHT ON THE AIR- CONDITIONING PANEL. AN UNEVENTFUL RETURN TO SLC ARPT WAS ACCOMPLISHED. ALL NECESSARY CHKLISTS WERE ACCOMPLISHED AT THE APPROPRIATE TIME. NO PAX OR CREW MEMBERS WERE HURT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR FLIES THE B-757 AND DOES NOT KNOW WHAT CAUSED THE PRESSURIZATION PROB. HE KNOWS THAT SEVERAL 'BLACK BOXES' WERE CHANGED. HE BELIEVES THAT HE TOOK OFF 'WITH THE BETTER PACK' DISABLED PER MEL. HIS ACR'S FAA LIAISON TALKED DIRECTLY WITH THE ARTCC CTLR THAT DENIED THE LOWER ALT. THE CTLR 'HAD A PLAN' FOR GIVING A LOWER ALT AFTER TFC PASSED. THE RPTR'S TRIP WAS CANCELED AND HE HAS NOT FLOWN THIS ACFT SINCE THE DAY OF THE INCIDENT.

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.