Narrative:

During cruise at FL390 the 'essential standby power' light on the pilot's caution warning panel illuminated. No other indications. 30 seconds later, the 'dc standby buss' failure light on the flight engineer's panel illuminated. All other busses -- AC and dc -- were pwred. This is a most unusual situation since the 'dc standby buss' is the last buss to lose power and is pwred several different ways. As the captain and flight engineer worked the problem the cabin began to rise, slowly at first and then unctlably. The pressurization system was completely uncontrollable in all 3 modes, and all subsystems were not working as well. At this point, we donned our oxygen masks and initiated an emergency descent, notified ATC and declared an emergency, communicated with the senior flight attendant and made a PA to the passenger. The captain and flight engineer continued to work the problems as I executed the emergency descent. As I leveled at 14000 ft, the flight engineer regained control of the pressurization system, once that was stabilized we decided to remain at 14000 ft. After contacting dispatch, we decided that with the fuel remaining it was safe to continue to the destination. Considering the nature of the flight, diverting to cairo was an unattractive option. After securing all checklists the captain, sent the flight engineer back to the cabin to evaluate the situation. Fortunately, there were no injuries and the passenger were in good spirits. The flight continued to the destination uneventfully. We know what happened, just not why. For the 'standby dc buss' to fail on its own and have the outflow valves drive open with a pressurization failure defies logic, but it happened. Thanks to good training, this event went smoothly. Everyone knew their roles and performed without a glitch. Good communication was maintained between the cabin and flight deck which helped in keeping the passenger informed.

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Original NASA ASRS Text

Title: L1011 FLC EXPERIENCED A LOSS OF CABIN PRESSURE AT FL390. AN EMER DSCNT WAS INITIATED TO 14000 FT WHERE CTL WAS REGAINED.

Narrative: DURING CRUISE AT FL390 THE 'ESSENTIAL STANDBY PWR' LIGHT ON THE PLT'S CAUTION WARNING PANEL ILLUMINATED. NO OTHER INDICATIONS. 30 SECONDS LATER, THE 'DC STANDBY BUSS' FAILURE LIGHT ON THE FE'S PANEL ILLUMINATED. ALL OTHER BUSSES -- AC AND DC -- WERE PWRED. THIS IS A MOST UNUSUAL SIT SINCE THE 'DC STANDBY BUSS' IS THE LAST BUSS TO LOSE PWR AND IS PWRED SEVERAL DIFFERENT WAYS. AS THE CAPT AND FE WORKED THE PROB THE CABIN BEGAN TO RISE, SLOWLY AT FIRST AND THEN UNCTLABLY. THE PRESSURIZATION SYS WAS COMPLETELY UNCTLABLE IN ALL 3 MODES, AND ALL SUBSYSTEMS WERE NOT WORKING AS WELL. AT THIS POINT, WE DONNED OUR OXYGEN MASKS AND INITIATED AN EMER DSCNT, NOTIFIED ATC AND DECLARED AN EMER, COMMUNICATED WITH THE SENIOR FLT ATTENDANT AND MADE A PA TO THE PAX. THE CAPT AND FE CONTINUED TO WORK THE PROBS AS I EXECUTED THE EMER DSCNT. AS I LEVELED AT 14000 FT, THE FE REGAINED CTL OF THE PRESSURIZATION SYS, ONCE THAT WAS STABILIZED WE DECIDED TO REMAIN AT 14000 FT. AFTER CONTACTING DISPATCH, WE DECIDED THAT WITH THE FUEL REMAINING IT WAS SAFE TO CONTINUE TO THE DEST. CONSIDERING THE NATURE OF THE FLT, DIVERTING TO CAIRO WAS AN UNATTRACTIVE OPTION. AFTER SECURING ALL CHKLISTS THE CAPT, SENT THE FE BACK TO THE CABIN TO EVALUATE THE SIT. FORTUNATELY, THERE WERE NO INJURIES AND THE PAX WERE IN GOOD SPIRITS. THE FLT CONTINUED TO THE DEST UNEVENTFULLY. WE KNOW WHAT HAPPENED, JUST NOT WHY. FOR THE 'STANDBY DC BUSS' TO FAIL ON ITS OWN AND HAVE THE OUTFLOW VALVES DRIVE OPEN WITH A PRESSURIZATION FAILURE DEFIES LOGIC, BUT IT HAPPENED. THANKS TO GOOD TRAINING, THIS EVENT WENT SMOOTHLY. EVERYONE KNEW THEIR ROLES AND PERFORMED WITHOUT A GLITCH. GOOD COM WAS MAINTAINED BTWN THE CABIN AND FLT DECK WHICH HELPED IN KEEPING THE PAX INFORMED.

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.