Narrative:

Climbing through approximately FL246 on our way to FL250, the first officer noticed the cabin altitude was about 9800 ft and remarked it seemed excessive. I asked center to descend to FL240. The controller responded 'roger.' at that point, the cabin altitude went above 10000 ft and we received the cabin pressure warning. We, the first officer, leveled off as we began the aom procedures. I asked the controller for the descent again right before the warning. He said 'I have your request, say your altitude now.' during this exchange, the first officer had started his descent as I was putting on my oxygen mask. Once we were on oxygen, I advised center we were declaring an emergency due to cabin pressurization and would like to continue descent. Eventually at 10000 ft, after following all checklists per operating manual, the pressurization was stabilized by using the manual mode. After conferring with company dispatch and maintenance control, the decision was made to continue to dfw. There was no doubt of structural integrity. Since we no longer required priority handling, ATC asked if we wanted to cancel the emergency. We said yes and continued to dfw without event. I'm not sure what caused the excessive cabin altitude, but my lack of situational awareness in scanning the cabin pressurization panel during the climb out prevented us from remedying the problem, ie, cabin altitude above 10000 ft, before it got to that point which dictated a descent or emergency descent. Since the controller didn't issue a descent right off, we had to declare the emergency and descend since the cabin altitude had reached approximately 13000 ft. Since we rarely go above FL190 on our short trips, the pressurization is not usually an issue. Most of my trips recently have been short flts, around 10000 ft. This has probably led to the lack of scan. Needless to say, this occurrence has renewed my scan of all system during climb out. There were no injuries or aircraft damage. I believe the only emergency was to descend in order to assure the cabin altitude descended. There was no decompression in any manner. The manual mode did pressurize the aircraft. The pressurization is always an issue, to re-explain, it's just that the pressurization check, on the checklist is only on the initial climb checklist and on the descent checklist. One should scan the system at regular intervals of course, but having another pressurization check on the cruise checklist might help, even though in this case, we were still a few hundred ft from cruise altitude. Possible causes for the excessive cabin altitude, which was a gradual increase, could possibly have been the automatic controller at fault or the secondary outflow valve being cracked open by the manual know being misaligned or accidentally brushed against by something. At this time I don't know.

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Original NASA ASRS Text

Title: SF340 FLC DECLARED AN EMER AND DSNDED DUE TO NOTICING THE CABIN ALT CLBING TO AN UNACCEPTABLE ALT.

Narrative: CLBING THROUGH APPROX FL246 ON OUR WAY TO FL250, THE FO NOTICED THE CABIN ALT WAS ABOUT 9800 FT AND REMARKED IT SEEMED EXCESSIVE. I ASKED CTR TO DSND TO FL240. THE CTLR RESPONDED 'ROGER.' AT THAT POINT, THE CABIN ALT WENT ABOVE 10000 FT AND WE RECEIVED THE CABIN PRESSURE WARNING. WE, THE FO, LEVELED OFF AS WE BEGAN THE AOM PROCS. I ASKED THE CTLR FOR THE DSCNT AGAIN RIGHT BEFORE THE WARNING. HE SAID 'I HAVE YOUR REQUEST, SAY YOUR ALT NOW.' DURING THIS EXCHANGE, THE FO HAD STARTED HIS DSCNT AS I WAS PUTTING ON MY OXYGEN MASK. ONCE WE WERE ON OXYGEN, I ADVISED CTR WE WERE DECLARING AN EMER DUE TO CABIN PRESSURIZATION AND WOULD LIKE TO CONTINUE DSCNT. EVENTUALLY AT 10000 FT, AFTER FOLLOWING ALL CHKLISTS PER OPERATING MANUAL, THE PRESSURIZATION WAS STABILIZED BY USING THE MANUAL MODE. AFTER CONFERRING WITH COMPANY DISPATCH AND MAINT CTL, THE DECISION WAS MADE TO CONTINUE TO DFW. THERE WAS NO DOUBT OF STRUCTURAL INTEGRITY. SINCE WE NO LONGER REQUIRED PRIORITY HANDLING, ATC ASKED IF WE WANTED TO CANCEL THE EMER. WE SAID YES AND CONTINUED TO DFW WITHOUT EVENT. I'M NOT SURE WHAT CAUSED THE EXCESSIVE CABIN ALT, BUT MY LACK OF SITUATIONAL AWARENESS IN SCANNING THE CABIN PRESSURIZATION PANEL DURING THE CLBOUT PREVENTED US FROM REMEDYING THE PROB, IE, CABIN ALT ABOVE 10000 FT, BEFORE IT GOT TO THAT POINT WHICH DICTATED A DSCNT OR EMER DSCNT. SINCE THE CTLR DIDN'T ISSUE A DSCNT RIGHT OFF, WE HAD TO DECLARE THE EMER AND DSND SINCE THE CABIN ALT HAD REACHED APPROX 13000 FT. SINCE WE RARELY GO ABOVE FL190 ON OUR SHORT TRIPS, THE PRESSURIZATION IS NOT USUALLY AN ISSUE. MOST OF MY TRIPS RECENTLY HAVE BEEN SHORT FLTS, AROUND 10000 FT. THIS HAS PROBABLY LED TO THE LACK OF SCAN. NEEDLESS TO SAY, THIS OCCURRENCE HAS RENEWED MY SCAN OF ALL SYS DURING CLBOUT. THERE WERE NO INJURIES OR ACFT DAMAGE. I BELIEVE THE ONLY EMER WAS TO DSND IN ORDER TO ASSURE THE CABIN ALT DSNDED. THERE WAS NO DECOMPRESSION IN ANY MANNER. THE MANUAL MODE DID PRESSURIZE THE ACFT. THE PRESSURIZATION IS ALWAYS AN ISSUE, TO RE-EXPLAIN, IT'S JUST THAT THE PRESSURIZATION CHK, ON THE CHKLIST IS ONLY ON THE INITIAL CLB CHKLIST AND ON THE DSCNT CHKLIST. ONE SHOULD SCAN THE SYS AT REGULAR INTERVALS OF COURSE, BUT HAVING ANOTHER PRESSURIZATION CHK ON THE CRUISE CHKLIST MIGHT HELP, EVEN THOUGH IN THIS CASE, WE WERE STILL A FEW HUNDRED FT FROM CRUISE ALT. POSSIBLE CAUSES FOR THE EXCESSIVE CABIN ALT, WHICH WAS A GRADUAL INCREASE, COULD POSSIBLY HAVE BEEN THE AUTOMATIC CONTROLLER AT FAULT OR THE SECONDARY OUTFLOW VALVE BEING CRACKED OPEN BY THE MANUAL KNOW BEING MISALIGNED OR ACCIDENTALLY BRUSHED AGAINST BY SOMETHING. AT THIS TIME I DON'T KNOW.

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.