Narrative:

Flight was the second leg of the first day of a 2-DAY pairing. We were filed for FL350. On climb out we looked at the cruise page and noticed our optimum cruise altitude was 33400 ft; so we requested FL330 and received it; with the intention of climbing up to our filed altitude shortly. The first officer set in the 330 in the MCP and I set 330 in the FMC. Since we were planning on going up to FL350 in what I figured would be a short amount of time; to the first officer I said something to the effect of 'you can leave it; we'll be up there in a bit' referring to the pressurization control panel. The flight proceeded smoothly and; guess what; we never did climb to FL350. The ride was smooth and we had plenty of gas. We started our descent into den and got the 'off sched descent' light -- just like we should have. The air condition annunciator came on and I looked up and saw the 'off sched descent' light and quickly realized we never did reach FL350. I canceled the light and said 'checked per the condition.' the only explanation for this I can think of is that I had just got out of recurrent 2 days prior and with multiple malfunctions that have us never reaching our climb altitude; we are often getting the 'off-sched descent' light and saying 'checked per the condition.' as far as I recall; for expediency in the simulator; we don't bring out the checklist for it; because we know what happened and we are going back to the field we took off from. That's the key here -- we weren't going back to the field we took off from. We were going to a field; 5000 ft higher than the one we took off from. Unfortunately; habit patterns are developed and mine that day had me saying 'checked per the condition.' the descent continued and the 'off sched descent' light came on 2 more times I believe. Each time; I canceled it and said 'checked per the condition.' after this 3RD time; the first officer who was the PF sensed something wasn't right and looked up to check the pressurization and noticed the cabin altitude was well below our landing altitude (cabin was around 2700 ft). Great catch. At this time it fully dawned on me why we kept getting the 'off sched descent' light -- it was for a good reason. We had just descended through 10000 ft MSL and I figured it would take too long to bring the cabin pressure up by resetting the cruise altitude (or frankly if that method would have even worked now). Also; I am not sure if leaving it as it was would have been ok and the outflow valve would have moved slowly enough to the open position upon putting the switch to ground to make it a controllable change in cabin altitude. So I opted to adjust the cabin altitude by using the pressurization in the manual mode. I toggled and released the outflow valve switch to 'open' as briefly as possible a couple times until the cabin altitude came up to just over 4000 ft and then put the controller back in automatic. We landed uneventfully and taxied to the gate. I stood at the door and said goodbye and thank you to our passenger and no one commented about the pressurization; as it was very minor; albeit more than a normal rate of change. The flight attendants of course noticed; but said it wasn't a big deal and that none of the passenger commented. Lessons learned: if a light comes on that has an associated checklist -- always do it; regardless of prior experience.

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Original NASA ASRS Text

Title: B737-400 FLT CREW ENRTE TO DEN FAILS TO REPROGRAM AUTO PRESSURE CTLR WHEN THEY STOP CLB SHORT OF ORIGINAL PLANNED CRUISE ALT. PRESSURE CTLR THEREFORE PLANS A CABIN ALT AT TOUCHDOWN OF THE ALT AT THE DEP STATION.

Narrative: FLT WAS THE SECOND LEG OF THE FIRST DAY OF A 2-DAY PAIRING. WE WERE FILED FOR FL350. ON CLBOUT WE LOOKED AT THE CRUISE PAGE AND NOTICED OUR OPTIMUM CRUISE ALT WAS 33400 FT; SO WE REQUESTED FL330 AND RECEIVED IT; WITH THE INTENTION OF CLBING UP TO OUR FILED ALT SHORTLY. THE FO SET IN THE 330 IN THE MCP AND I SET 330 IN THE FMC. SINCE WE WERE PLANNING ON GOING UP TO FL350 IN WHAT I FIGURED WOULD BE A SHORT AMOUNT OF TIME; TO THE FO I SAID SOMETHING TO THE EFFECT OF 'YOU CAN LEAVE IT; WE'LL BE UP THERE IN A BIT' REFERRING TO THE PRESSURIZATION CTL PANEL. THE FLT PROCEEDED SMOOTHLY AND; GUESS WHAT; WE NEVER DID CLB TO FL350. THE RIDE WAS SMOOTH AND WE HAD PLENTY OF GAS. WE STARTED OUR DSCNT INTO DEN AND GOT THE 'OFF SCHED DSCNT' LIGHT -- JUST LIKE WE SHOULD HAVE. THE AIR CONDITION ANNUNCIATOR CAME ON AND I LOOKED UP AND SAW THE 'OFF SCHED DSCNT' LIGHT AND QUICKLY REALIZED WE NEVER DID REACH FL350. I CANCELED THE LIGHT AND SAID 'CHKED PER THE CONDITION.' THE ONLY EXPLANATION FOR THIS I CAN THINK OF IS THAT I HAD JUST GOT OUT OF RECURRENT 2 DAYS PRIOR AND WITH MULTIPLE MALFUNCTIONS THAT HAVE US NEVER REACHING OUR CLB ALT; WE ARE OFTEN GETTING THE 'OFF-SCHED DSCNT' LIGHT AND SAYING 'CHKED PER THE CONDITION.' AS FAR AS I RECALL; FOR EXPEDIENCY IN THE SIMULATOR; WE DON'T BRING OUT THE CHKLIST FOR IT; BECAUSE WE KNOW WHAT HAPPENED AND WE ARE GOING BACK TO THE FIELD WE TOOK OFF FROM. THAT'S THE KEY HERE -- WE WEREN'T GOING BACK TO THE FIELD WE TOOK OFF FROM. WE WERE GOING TO A FIELD; 5000 FT HIGHER THAN THE ONE WE TOOK OFF FROM. UNFORTUNATELY; HABIT PATTERNS ARE DEVELOPED AND MINE THAT DAY HAD ME SAYING 'CHKED PER THE CONDITION.' THE DSCNT CONTINUED AND THE 'OFF SCHED DSCNT' LIGHT CAME ON 2 MORE TIMES I BELIEVE. EACH TIME; I CANCELED IT AND SAID 'CHKED PER THE CONDITION.' AFTER THIS 3RD TIME; THE FO WHO WAS THE PF SENSED SOMETHING WASN'T RIGHT AND LOOKED UP TO CHK THE PRESSURIZATION AND NOTICED THE CABIN ALT WAS WELL BELOW OUR LNDG ALT (CABIN WAS AROUND 2700 FT). GREAT CATCH. AT THIS TIME IT FULLY DAWNED ON ME WHY WE KEPT GETTING THE 'OFF SCHED DSCNT' LIGHT -- IT WAS FOR A GOOD REASON. WE HAD JUST DSNDED THROUGH 10000 FT MSL AND I FIGURED IT WOULD TAKE TOO LONG TO BRING THE CABIN PRESSURE UP BY RESETTING THE CRUISE ALT (OR FRANKLY IF THAT METHOD WOULD HAVE EVEN WORKED NOW). ALSO; I AM NOT SURE IF LEAVING IT AS IT WAS WOULD HAVE BEEN OK AND THE OUTFLOW VALVE WOULD HAVE MOVED SLOWLY ENOUGH TO THE OPEN POS UPON PUTTING THE SWITCH TO GND TO MAKE IT A CONTROLLABLE CHANGE IN CABIN ALT. SO I OPTED TO ADJUST THE CABIN ALT BY USING THE PRESSURIZATION IN THE MANUAL MODE. I TOGGLED AND RELEASED THE OUTFLOW VALVE SWITCH TO 'OPEN' AS BRIEFLY AS POSSIBLE A COUPLE TIMES UNTIL THE CABIN ALT CAME UP TO JUST OVER 4000 FT AND THEN PUT THE CTLR BACK IN AUTO. WE LANDED UNEVENTFULLY AND TAXIED TO THE GATE. I STOOD AT THE DOOR AND SAID GOODBYE AND THANK YOU TO OUR PAX AND NO ONE COMMENTED ABOUT THE PRESSURIZATION; AS IT WAS VERY MINOR; ALBEIT MORE THAN A NORMAL RATE OF CHANGE. THE FLT ATTENDANTS OF COURSE NOTICED; BUT SAID IT WASN'T A BIG DEAL AND THAT NONE OF THE PAX COMMENTED. LESSONS LEARNED: IF A LIGHT COMES ON THAT HAS AN ASSOCIATED CHKLIST -- ALWAYS DO IT; REGARDLESS OF PRIOR EXPERIENCE.

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