Narrative:

During level cruise at FL410. Our primary pressurization source (air cycle machine) failed and the secondary pressurization source failed to activate automatically. The captain called for the emergency pressurization checklist and emergency pressurization was then selected manually. At this point the cabin vsi was showing a 4000 FPM climb and the master warning and 'cabin altitude 10000'' lights had illuminated. It appeared that no pressurized air was entering the cabin. The captain told me to request a lower altitude and we both donned our O2 masks. I called the center, 'request lower altitude, immediately.' center: 'roger, descend and maintain FL270, are you declaring an emergency.' I replied, 'not at this time, we're having pressurization problems.' 1 min later the captain told me, 'go ahead and declare the emergency, we need to get lower.' I called the center and declared the emergency. The frequency was very busy, the controller was talking with several other aircraft. I'm not sure if he heard this transmission. The captain leveled at FL270 briefly and then decided to continue the descent. A few seconds later the controller asked us, 'what's your altitude?' I told him we were 'declaring' and descending to 10000'. We descended west/O any further difficulty and continued on our previous routing at 10000' which we determined the proper course of action. This situation reminded me again of the importance of clear communication when dealing with a problem like this. ATC should do their best to keep the frequency clear of non essential conversation any time an aircraft reports a problem. Flight crews need to practice crew coordination and running checklists with O2 masks on. My own training in emergency dscnts focused on 'how to descend to the aircraft' and not how to work with another pilot in such a cumbersome and stressful situation. Supplemental information from acn 165008: the cabin was repressurized and we climbed to 22000'. I believe the loss of cabin pressure was due to icing over of water separator in acm (a poorly designed system). When this happens the left engine provides bleed air to pressurize the cabin. This emergency system did not work when we needed it most. Once we repressurized at 10000' we should or could have landed at the nearest suitable airport.

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Original NASA ASRS Text

Title: CPR LTT LOST CABIN PRESSURIZATION AT FL410. RECEIVED CLRNC TO FL270 AND WHEN THIS WAS NOT LOW ENOUGH CONTINUED DESCENT TO 10000'. EMERGENCY DECLARED BUT AFTER ACFT HAD LEFT FL270 WITHOUT CLRNC.

Narrative: DURING LEVEL CRUISE AT FL410. OUR PRIMARY PRESSURIZATION SOURCE (AIR CYCLE MACHINE) FAILED AND THE SECONDARY PRESSURIZATION SOURCE FAILED TO ACTIVATE AUTOMATICALLY. THE CAPT CALLED FOR THE EMER PRESSURIZATION CHECKLIST AND EMER PRESSURIZATION WAS THEN SELECTED MANUALLY. AT THIS POINT THE CABIN VSI WAS SHOWING A 4000 FPM CLB AND THE MASTER WARNING AND 'CABIN ALT 10000'' LIGHTS HAD ILLUMINATED. IT APPEARED THAT NO PRESSURIZED AIR WAS ENTERING THE CABIN. THE CAPT TOLD ME TO REQUEST A LOWER ALT AND WE BOTH DONNED OUR O2 MASKS. I CALLED THE CENTER, 'REQUEST LOWER ALT, IMMEDIATELY.' CENTER: 'ROGER, DSND AND MAINTAIN FL270, ARE YOU DECLARING AN EMER.' I REPLIED, 'NOT AT THIS TIME, WE'RE HAVING PRESSURIZATION PROBS.' 1 MIN LATER THE CAPT TOLD ME, 'GO AHEAD AND DECLARE THE EMER, WE NEED TO GET LOWER.' I CALLED THE CENTER AND DECLARED THE EMER. THE FREQ WAS VERY BUSY, THE CTLR WAS TALKING WITH SEVERAL OTHER ACFT. I'M NOT SURE IF HE HEARD THIS XMISSION. THE CAPT LEVELED AT FL270 BRIEFLY AND THEN DECIDED TO CONTINUE THE DSNT. A FEW SECS LATER THE CTLR ASKED US, 'WHAT'S YOUR ALT?' I TOLD HIM WE WERE 'DECLARING' AND DSNDING TO 10000'. WE DSNDED W/O ANY FURTHER DIFFICULTY AND CONTINUED ON OUR PREVIOUS RTING AT 10000' WHICH WE DETERMINED THE PROPER COURSE OF ACTION. THIS SITUATION REMINDED ME AGAIN OF THE IMPORTANCE OF CLR COM WHEN DEALING WITH A PROB LIKE THIS. ATC SHOULD DO THEIR BEST TO KEEP THE FREQ CLR OF NON ESSENTIAL CONVERSATION ANY TIME AN ACFT RPTS A PROB. FLT CREWS NEED TO PRACTICE CREW COORD AND RUNNING CHKLISTS WITH O2 MASKS ON. MY OWN TRNING IN EMER DSCNTS FOCUSED ON 'HOW TO DSND TO THE ACFT' AND NOT HOW TO WORK WITH ANOTHER PLT IN SUCH A CUMBERSOME AND STRESSFUL SITUATION. SUPPLEMENTAL INFO FROM ACN 165008: THE CABIN WAS REPRESSURIZED AND WE CLBED TO 22000'. I BELIEVE THE LOSS OF CABIN PRESSURE WAS DUE TO ICING OVER OF WATER SEPARATOR IN ACM (A POORLY DESIGNED SYS). WHEN THIS HAPPENS THE LEFT ENG PROVIDES BLEED AIR TO PRESSURIZE THE CABIN. THIS EMER SYS DID NOT WORK WHEN WE NEEDED IT MOST. ONCE WE REPRESSURIZED AT 10000' WE SHOULD OR COULD HAVE LANDED AT THE NEAREST SUITABLE ARPT.

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.