Narrative:

Our flight departed sna at XA10 with a normal noise abatement takeoff procedure used (TOGW 127500 pounds with maximum power, flaps 5 degrees, cutback and power restored altitude at 4000 ft). A no engine bleed procedure was used for this departure. The after takeoff checklist was initiated at 6000 ft, due to the extended climb phase for noise abatement. We were stepped climbed to 10000 ft, direct lax, then 14000 ft, 16000 ft, and finally FL260. Passing approximately FL230 and approaching the vicinity of ehf VOR, the cabin altitude warning horn sounded. Before we could react to the horn, the master caution, overhead and passenger oxygen on lights illuminated. Realizing our mistake, the engine bleeds were immediately turned back on and the cabin pressurized in 'automatic.' the depressurization checklist was reviewed and the captain placed the pressurization system into 'manual' mode. This pressurized the cabin faster and after a cabin altitude of less than 10000 ft, I placed the controller back to 'automatic.' the captain went on the PA system to communicate with the passenger and intercom system to coordinate with the rest of the flight crew. I continued to monitor ATC and the autoplt. The captain asked for a lower altitude, but was denied due to traffic. We assessed the situation and noted that the aircraft was pressurized and through crew coordination, we had enough oxygen to continue to destination. According to the lead flight attendant, upon descent, some passenger were activating their oxygen 'just to try it.' our flight arrived with an uneventful landing at XB13. Looking back, the problem started with not reconfiguring the engine bleeds during the after takeoff checklist. This can be attributed to a couple of things: 1) this particular procedure was around 1 month old to our company and not all crews were using it. 2) it was a rather busy night over the los angeles basin and along with a departure report, my radio calls were somewhat continuous. Another contributing factor is that the cabin altitude warning horn was misidented as the confign warning horn. This may be due to the fact that all of our rapid decompression training in the simulator is done in the cruise phase of flight. Also of importance is the similarity between both warning horns. The error chain, once realized, was quickly broken when coordination and training came into play. The ability to stay focused and not to look back at the 'we should've' and 'we could've' played a major role. If any member of our crew got fixated on the mistake, thus continuing the error chain, the incident may have turned out a lot worse.

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Original NASA ASRS Text

Title: A B737-700 FLT CREW INADVERTENTLY FORGET TO TURN BACK ON THE PACKS AFTER TKOF AND INITIALLY MISINTERPRETED THE ALT WARNING HORN AS HAVING AN ACFT CONFIGURATION PROB. THE RPTR STATES THAT THE DUAL USE WARNING HORN CONTRIBUTED TO THE DELAYED RECOGNITION AND THE DEPLOYMENT OF THE O2 MASKS.

Narrative: OUR FLT DEPARTED SNA AT XA10 WITH A NORMAL NOISE ABATEMENT TKOF PROC USED (TOGW 127500 LBS WITH MAX PWR, FLAPS 5 DEGS, CUTBACK AND PWR RESTORED ALT AT 4000 FT). A NO ENG BLEED PROC WAS USED FOR THIS DEP. THE AFTER TKOF CHKLIST WAS INITIATED AT 6000 FT, DUE TO THE EXTENDED CLB PHASE FOR NOISE ABATEMENT. WE WERE STEPPED CLBED TO 10000 FT, DIRECT LAX, THEN 14000 FT, 16000 FT, AND FINALLY FL260. PASSING APPROX FL230 AND APCHING THE VICINITY OF EHF VOR, THE CABIN ALT WARNING HORN SOUNDED. BEFORE WE COULD REACT TO THE HORN, THE MASTER CAUTION, OVERHEAD AND PAX OXYGEN ON LIGHTS ILLUMINATED. REALIZING OUR MISTAKE, THE ENG BLEEDS WERE IMMEDIATELY TURNED BACK ON AND THE CABIN PRESSURIZED IN 'AUTO.' THE DEPRESSURIZATION CHKLIST WAS REVIEWED AND THE CAPT PLACED THE PRESSURIZATION SYS INTO 'MANUAL' MODE. THIS PRESSURIZED THE CABIN FASTER AND AFTER A CABIN ALT OF LESS THAN 10000 FT, I PLACED THE CONTROLLER BACK TO 'AUTO.' THE CAPT WENT ON THE PA SYS TO COMMUNICATE WITH THE PAX AND INTERCOM SYS TO COORDINATE WITH THE REST OF THE FLT CREW. I CONTINUED TO MONITOR ATC AND THE AUTOPLT. THE CAPT ASKED FOR A LOWER ALT, BUT WAS DENIED DUE TO TFC. WE ASSESSED THE SIT AND NOTED THAT THE ACFT WAS PRESSURIZED AND THROUGH CREW COORD, WE HAD ENOUGH OXYGEN TO CONTINUE TO DEST. ACCORDING TO THE LEAD FLT ATTENDANT, UPON DSCNT, SOME PAX WERE ACTIVATING THEIR OXYGEN 'JUST TO TRY IT.' OUR FLT ARRIVED WITH AN UNEVENTFUL LNDG AT XB13. LOOKING BACK, THE PROB STARTED WITH NOT RECONFIGURING THE ENG BLEEDS DURING THE AFTER TKOF CHKLIST. THIS CAN BE ATTRIBUTED TO A COUPLE OF THINGS: 1) THIS PARTICULAR PROC WAS AROUND 1 MONTH OLD TO OUR COMPANY AND NOT ALL CREWS WERE USING IT. 2) IT WAS A RATHER BUSY NIGHT OVER THE LOS ANGELES BASIN AND ALONG WITH A DEP RPT, MY RADIO CALLS WERE SOMEWHAT CONTINUOUS. ANOTHER CONTRIBUTING FACTOR IS THAT THE CABIN ALT WARNING HORN WAS MISIDENTED AS THE CONFIGN WARNING HORN. THIS MAY BE DUE TO THE FACT THAT ALL OF OUR RAPID DECOMPRESSION TRAINING IN THE SIMULATOR IS DONE IN THE CRUISE PHASE OF FLT. ALSO OF IMPORTANCE IS THE SIMILARITY BTWN BOTH WARNING HORNS. THE ERROR CHAIN, ONCE REALIZED, WAS QUICKLY BROKEN WHEN COORD AND TRAINING CAME INTO PLAY. THE ABILITY TO STAY FOCUSED AND NOT TO LOOK BACK AT THE 'WE SHOULD'VE' AND 'WE COULD'VE' PLAYED A MAJOR ROLE. IF ANY MEMBER OF OUR CREW GOT FIXATED ON THE MISTAKE, THUS CONTINUING THE ERROR CHAIN, THE INCIDENT MAY HAVE TURNED OUT A LOT WORSE.

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.