Narrative:

First officer was PF. Day started uneventful. Engine start uneventful. Passing 13000 ft the altitude warning horn activated. I leveled off as the captain checked the cabin altimeter. It read 10000 ft. Captain requested a leveloff and a descent to 10000 ft from ATC. The pressurization panel was checked and noted that the pack switches were off. I set the switches to automatic. The cabin altitude started to come back down. We ran the QRH before continuing our climb. After beating ourselves over the head about checklist discipline and how many times we looked but did not see; it came down to 'I' missed the pack switches 3 times. Once after start; once before takeoff; and once during the 10000 ft check. After the engine start checklist while I was accomplishing my after start flow; the captain turned off the cockpit light. The cockpit was totally dark and I asked if I could turn on the light again. I then failed to set the packs to automatic. The next opportunity to catch the switches was the before takeoff check. We had just started running the checklist when tower asked us to pull up to #1. The item was called from the checklist and again with a dark cockpit; I looked at the panel but did not see; and accepted the appropriate response. With the climb check still to come; it is hard to believe that this item was missed a third time. This should have been the place to find the error; aircraft pressurization and the pack switches; along with confirming the cabin temperature; which; ironically; was accomplished. There is no excuse that can justify my actions except for the initial interruption and complacency. I've read safety reports; and they have been very helpful. I am just ashamed that I didn't do what I was supposed to do. And yes; the cabin altitude warning horn does sound like the gear warning horn. Following company policy on checklist discipline will eliminate this event in the future. Paying lip service gets you nowhere. Call for an item on the checklist; listen to the response; and verify the position of the switch.

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Original NASA ASRS Text

Title: B737 CREW GETS CABIN ALT WARNING HORN DURING CLBOUT DUE TO PACK SWITCHES BEING OFF.

Narrative: FO WAS PF. DAY STARTED UNEVENTFUL. ENG START UNEVENTFUL. PASSING 13000 FT THE ALT WARNING HORN ACTIVATED. I LEVELED OFF AS THE CAPT CHKED THE CABIN ALTIMETER. IT READ 10000 FT. CAPT REQUESTED A LEVELOFF AND A DSCNT TO 10000 FT FROM ATC. THE PRESSURIZATION PANEL WAS CHKED AND NOTED THAT THE PACK SWITCHES WERE OFF. I SET THE SWITCHES TO AUTO. THE CABIN ALT STARTED TO COME BACK DOWN. WE RAN THE QRH BEFORE CONTINUING OUR CLB. AFTER BEATING OURSELVES OVER THE HEAD ABOUT CHKLIST DISCIPLINE AND HOW MANY TIMES WE LOOKED BUT DID NOT SEE; IT CAME DOWN TO 'I' MISSED THE PACK SWITCHES 3 TIMES. ONCE AFTER START; ONCE BEFORE TKOF; AND ONCE DURING THE 10000 FT CHK. AFTER THE ENG START CHKLIST WHILE I WAS ACCOMPLISHING MY AFTER START FLOW; THE CAPT TURNED OFF THE COCKPIT LIGHT. THE COCKPIT WAS TOTALLY DARK AND I ASKED IF I COULD TURN ON THE LIGHT AGAIN. I THEN FAILED TO SET THE PACKS TO AUTO. THE NEXT OPPORTUNITY TO CATCH THE SWITCHES WAS THE BEFORE TKOF CHK. WE HAD JUST STARTED RUNNING THE CHKLIST WHEN TWR ASKED US TO PULL UP TO #1. THE ITEM WAS CALLED FROM THE CHKLIST AND AGAIN WITH A DARK COCKPIT; I LOOKED AT THE PANEL BUT DID NOT SEE; AND ACCEPTED THE APPROPRIATE RESPONSE. WITH THE CLB CHK STILL TO COME; IT IS HARD TO BELIEVE THAT THIS ITEM WAS MISSED A THIRD TIME. THIS SHOULD HAVE BEEN THE PLACE TO FIND THE ERROR; ACFT PRESSURIZATION AND THE PACK SWITCHES; ALONG WITH CONFIRMING THE CABIN TEMP; WHICH; IRONICALLY; WAS ACCOMPLISHED. THERE IS NO EXCUSE THAT CAN JUSTIFY MY ACTIONS EXCEPT FOR THE INITIAL INTERRUPTION AND COMPLACENCY. I'VE READ SAFETY RPTS; AND THEY HAVE BEEN VERY HELPFUL. I AM JUST ASHAMED THAT I DIDN'T DO WHAT I WAS SUPPOSED TO DO. AND YES; THE CABIN ALT WARNING HORN DOES SOUND LIKE THE GEAR WARNING HORN. FOLLOWING COMPANY POLICY ON CHKLIST DISCIPLINE WILL ELIMINATE THIS EVENT IN THE FUTURE. PAYING LIP SVC GETS YOU NOWHERE. CALL FOR AN ITEM ON THE CHKLIST; LISTEN TO THE RESPONSE; AND VERIFY THE POS OF THE SWITCH.

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.