Narrative:

We were flying from yyz to mke. Earlier en route to yyz we experienced problems with our cabin pressurization's system failure to pressurize aircraft. While I flew the aircraft, captain troubleshot the system. We consulted maintenance and were advised to operate in manual mode to pressurize aircraft. Flight continued normally with a descent and approach into yyz ILS runway 24L non eventfully. After landing, captain consulted maintenance back at mke. After discussion, we pulled appropriate circuit breakers and operated aircraft in manual mode. After an uneventful departure followed by quick right turn for WX. There were thunderstorms along the entire route to yyz and again on our departure. We were advised to contact yyz departure control. We were told to climb to FL280. Captain was flying aircraft. I was the PNF and I handled the communication as well as manually closing the pressure control lever (lollipop) to ensure aircraft pressurization. Manual control of the pressurization system is an inexact science and the system is very sensitive with cabin rate control spiking up and down as you close the lever closing the outflow valves. Ear drums are affected making it hard to hear and swallow. While climbing through FL240 for FL280, flight attendant came forward to advise us that the oxygen masks in the cabin had deployed. Captain and I both glanced up to the cabin altitude which indicated approximately 7500 ft with a cabin differential of 5 psi. We leveled off at FL240. I had closed the cabin pressure lollipop almost completely. I advised ATC of our leveloff at FL240. ATC queried us, did we have a problem? I stated we had a pressurization problem. ATC asked, 'were we declaring an emergency?' I stated, 'negative' but restated that, 'we needed to level off at FL240.' ATC complied. During this exchange we were maneuvering around cells being painted on our radar. When we leveled off the master caution and a red cabin altitude warning light came on. Captain commanded us to don oxygen masks. We both quickly complied. While fumbling around for the intercom switches the captain stated she was initiating a descent and stated she wanted 12000 ft. I advised ATC that we needed 12000 ft. I did not initially hear the captain as her intercom button had not been pressed yet, therefore, it was some time before I became aware of the descent and informed ATC. They 'rogered' us while we were descending through FL240. The captain and I both concurred that the cabin was no longer climbing. I informed center and we requested FL180. ATC complied. We leveled off at FL180, and discontinued oxygen use. I became the PF and captain tried to troubleshoot the situation. Captain also was in contact with company maintenance and dispatch. We checked our numbers, fuel state, distance to go, WX at 16000 ft, our final leveloff altitude, and continued to mke. The captain made an uneventful landing. I believe the fact we were deviating around thunderstorms with the pressurization problem while changing frequencys, executing a quick descent, miscom on the flight deck due to oxygen mask and intercom usage led to not initially understanding captain's action that she was initiating a descent, and thereby communicating all this to center. Like most problems this began with a smaller problem that started a chain of events. Contributing to all this was bad WX, faulty equipment, early morning show time. With our company operations procedure, when we have 2 master cautions and a cabin altitude problem at FL260, procedure demands that we execute memory items. Also, we were unsure as to where our cabin altitude was going to. All of this indicated we should descend quickly. Perhaps taking a second or two to evaluate the situation could have helped. I believe we operated with good CRM and returned to our destination in a safe and professional manner with our passenger being kept informed as much as possible.

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Original NASA ASRS Text

Title: DC9-10 FLC EXPERIENCES A CABIN PRESSURIZATION PROB LEAVING YYZ FOR MKE. MAINT HAD, ON INBOUND LEG, ADVISED CREW TO OPERATE CTLS IN MANUAL MODE. THE CABIN PAX MASKS DEPLOYED ON CLBOUT FROM YYZ PRIOR TO ANY COCKPIT WARNING LIGHTS BEING ACTIVATED. IN THE ENSUING MELEE, THE CREW FAILED TO PROPERLY COMMUNICATE WITH ATC AND EACH OTHER, THUS GOING THROUGH 2 ALTDEVS AND FAILING TO DECLARE AN EMER.

Narrative: WE WERE FLYING FROM YYZ TO MKE. EARLIER ENRTE TO YYZ WE EXPERIENCED PROBS WITH OUR CABIN PRESSURIZATION'S SYS FAILURE TO PRESSURIZE ACFT. WHILE I FLEW THE ACFT, CAPT TROUBLESHOT THE SYS. WE CONSULTED MAINT AND WERE ADVISED TO OPERATE IN MANUAL MODE TO PRESSURIZE ACFT. FLT CONTINUED NORMALLY WITH A DSCNT AND APCH INTO YYZ ILS RWY 24L NON EVENTFULLY. AFTER LNDG, CAPT CONSULTED MAINT BACK AT MKE. AFTER DISCUSSION, WE PULLED APPROPRIATE CIRCUIT BREAKERS AND OPERATED ACFT IN MANUAL MODE. AFTER AN UNEVENTFUL DEP FOLLOWED BY QUICK R TURN FOR WX. THERE WERE TSTMS ALONG THE ENTIRE RTE TO YYZ AND AGAIN ON OUR DEP. WE WERE ADVISED TO CONTACT YYZ DEP CTL. WE WERE TOLD TO CLB TO FL280. CAPT WAS FLYING ACFT. I WAS THE PNF AND I HANDLED THE COM AS WELL AS MANUALLY CLOSING THE PRESSURE CTL LEVER (LOLLIPOP) TO ENSURE ACFT PRESSURIZATION. MANUAL CTL OF THE PRESSURIZATION SYS IS AN INEXACT SCIENCE AND THE SYS IS VERY SENSITIVE WITH CABIN RATE CTL SPIKING UP AND DOWN AS YOU CLOSE THE LEVER CLOSING THE OUTFLOW VALVES. EAR DRUMS ARE AFFECTED MAKING IT HARD TO HEAR AND SWALLOW. WHILE CLBING THROUGH FL240 FOR FL280, FLT ATTENDANT CAME FORWARD TO ADVISE US THAT THE OXYGEN MASKS IN THE CABIN HAD DEPLOYED. CAPT AND I BOTH GLANCED UP TO THE CABIN ALT WHICH INDICATED APPROX 7500 FT WITH A CABIN DIFFERENTIAL OF 5 PSI. WE LEVELED OFF AT FL240. I HAD CLOSED THE CABIN PRESSURE LOLLIPOP ALMOST COMPLETELY. I ADVISED ATC OF OUR LEVELOFF AT FL240. ATC QUERIED US, DID WE HAVE A PROB? I STATED WE HAD A PRESSURIZATION PROB. ATC ASKED, 'WERE WE DECLARING AN EMER?' I STATED, 'NEGATIVE' BUT RESTATED THAT, 'WE NEEDED TO LEVEL OFF AT FL240.' ATC COMPLIED. DURING THIS EXCHANGE WE WERE MANEUVERING AROUND CELLS BEING PAINTED ON OUR RADAR. WHEN WE LEVELED OFF THE MASTER CAUTION AND A RED CABIN ALT WARNING LIGHT CAME ON. CAPT COMMANDED US TO DON OXYGEN MASKS. WE BOTH QUICKLY COMPLIED. WHILE FUMBLING AROUND FOR THE INTERCOM SWITCHES THE CAPT STATED SHE WAS INITIATING A DSCNT AND STATED SHE WANTED 12000 FT. I ADVISED ATC THAT WE NEEDED 12000 FT. I DID NOT INITIALLY HEAR THE CAPT AS HER INTERCOM BUTTON HAD NOT BEEN PRESSED YET, THEREFORE, IT WAS SOME TIME BEFORE I BECAME AWARE OF THE DSCNT AND INFORMED ATC. THEY 'ROGERED' US WHILE WE WERE DSNDING THROUGH FL240. THE CAPT AND I BOTH CONCURRED THAT THE CABIN WAS NO LONGER CLBING. I INFORMED CTR AND WE REQUESTED FL180. ATC COMPLIED. WE LEVELED OFF AT FL180, AND DISCONTINUED OXYGEN USE. I BECAME THE PF AND CAPT TRIED TO TROUBLESHOOT THE SIT. CAPT ALSO WAS IN CONTACT WITH COMPANY MAINT AND DISPATCH. WE CHKED OUR NUMBERS, FUEL STATE, DISTANCE TO GO, WX AT 16000 FT, OUR FINAL LEVELOFF ALT, AND CONTINUED TO MKE. THE CAPT MADE AN UNEVENTFUL LNDG. I BELIEVE THE FACT WE WERE DEVIATING AROUND TSTMS WITH THE PRESSURIZATION PROB WHILE CHANGING FREQS, EXECUTING A QUICK DSCNT, MISCOM ON THE FLT DECK DUE TO OXYGEN MASK AND INTERCOM USAGE LED TO NOT INITIALLY UNDERSTANDING CAPT'S ACTION THAT SHE WAS INITIATING A DSCNT, AND THEREBY COMMUNICATING ALL THIS TO CTR. LIKE MOST PROBS THIS BEGAN WITH A SMALLER PROB THAT STARTED A CHAIN OF EVENTS. CONTRIBUTING TO ALL THIS WAS BAD WX, FAULTY EQUIP, EARLY MORNING SHOW TIME. WITH OUR COMPANY OPS PROC, WHEN WE HAVE 2 MASTER CAUTIONS AND A CABIN ALT PROB AT FL260, PROC DEMANDS THAT WE EXECUTE MEMORY ITEMS. ALSO, WE WERE UNSURE AS TO WHERE OUR CABIN ALT WAS GOING TO. ALL OF THIS INDICATED WE SHOULD DSND QUICKLY. PERHAPS TAKING A SECOND OR TWO TO EVALUATE THE SIT COULD HAVE HELPED. I BELIEVE WE OPERATED WITH GOOD CRM AND RETURNED TO OUR DESTINATION IN A SAFE AND PROFESSIONAL MANNER WITH OUR PAX BEING KEPT INFORMED AS MUCH AS POSSIBLE.

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.