Narrative:

On climb out; we experienced a cabin pressurization warning light at 12000 ft. We requested a descent to 10000 ft from approach and informed them we had a pressurization issue. We performed the appropriate checklists and found the automatic/manual/dump switch to be in the dump position. We returned it to automatic and continued without further incident. Prior to this flight; we had a maintenance issue which required maintenance to perform an engine run-up. When maintenance does this; they often place the automatic/manual/dump in dump. When they finished their run-up; they must not have returned it to automatic. As a crew; we should have caught the automatic/manual/dump wasn't in automatic during our before start check with the item; 'cabin altitude controls...set.' often times; we only check to make sure the altitude is correct and the correct barometric pressure is in. During the after takeoff and climb checks; the plane was pressurizing; but at a slower rate than normal; but going to ase it will take the cabin to 8000 ft before increasing the internal pressure differential. At 10000 ft; it showed 8000 ft which would appear normal. It took the extra 2000 ft to get it over 10000 ft. We reviewed what cabin altitude controls set means in the flight manual and recommend that others do as well. Perhaps; pressurization controller would be a better way to word this item so crew check more than the altitude. Also; maintenance should return the aircraft to the condition they found it in; or crews should be required to do an acceptance check after engine run-ups.

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Original NASA ASRS Text

Title: DHC8 FLT CREW ENCOUNTERS PRESSURIZATION PROBLEM AFTER TKOF. REPORTER INDICATES MAINT MAY HAVE LEFT THE PRESSURIZATION MODE SELECTOR IN THE DUMP POSITION FOLLOWING A MAINT RUN-UP.

Narrative: ON CLBOUT; WE EXPERIENCED A CABIN PRESSURIZATION WARNING LIGHT AT 12000 FT. WE REQUESTED A DSCNT TO 10000 FT FROM APCH AND INFORMED THEM WE HAD A PRESSURIZATION ISSUE. WE PERFORMED THE APPROPRIATE CHKLISTS AND FOUND THE AUTO/MANUAL/DUMP SWITCH TO BE IN THE DUMP POS. WE RETURNED IT TO AUTO AND CONTINUED WITHOUT FURTHER INCIDENT. PRIOR TO THIS FLT; WE HAD A MAINT ISSUE WHICH REQUIRED MAINT TO PERFORM AN ENG RUN-UP. WHEN MAINT DOES THIS; THEY OFTEN PLACE THE AUTO/MANUAL/DUMP IN DUMP. WHEN THEY FINISHED THEIR RUN-UP; THEY MUST NOT HAVE RETURNED IT TO AUTO. AS A CREW; WE SHOULD HAVE CAUGHT THE AUTO/MANUAL/DUMP WASN'T IN AUTO DURING OUR BEFORE START CHK WITH THE ITEM; 'CABIN ALT CTLS...SET.' OFTEN TIMES; WE ONLY CHK TO MAKE SURE THE ALT IS CORRECT AND THE CORRECT BAROMETRIC PRESSURE IS IN. DURING THE AFTER TKOF AND CLB CHKS; THE PLANE WAS PRESSURIZING; BUT AT A SLOWER RATE THAN NORMAL; BUT GOING TO ASE IT WILL TAKE THE CABIN TO 8000 FT BEFORE INCREASING THE INTERNAL PRESSURE DIFFERENTIAL. AT 10000 FT; IT SHOWED 8000 FT WHICH WOULD APPEAR NORMAL. IT TOOK THE EXTRA 2000 FT TO GET IT OVER 10000 FT. WE REVIEWED WHAT CABIN ALT CTLS SET MEANS IN THE FLT MANUAL AND RECOMMEND THAT OTHERS DO AS WELL. PERHAPS; PRESSURIZATION CONTROLLER WOULD BE A BETTER WAY TO WORD THIS ITEM SO CREW CHK MORE THAN THE ALT. ALSO; MAINT SHOULD RETURN THE ACFT TO THE CONDITION THEY FOUND IT IN; OR CREWS SHOULD BE REQUIRED TO DO AN ACCEPTANCE CHK AFTER ENG RUN-UPS.

Data retrieved from NASA's ASRS site as of May 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.