Narrative:

Aircraft departed den on night flight to sfo. Takeoff was conducted in SOP bleeds off takeoff confign. WX was a concern with thunderstorms on course so radar was tuned for thunderstorm avoidance. Captain (PF) handled flying and ATC communication while first officer left primary frequency to call company with outbound call on radio #2. Prior to leaving frequency, now at about 10000 ft MSL, first officer secures APU. Around 15000 ft MSL, first officer reports back on radio #1 after calling company. About FL200, the cabin altitude warning horn sounds. First officer silences horn, crew discovers cabin altitude at 10000 ft MSL and climbing. All caution and warning lights are not illuminated. Captain calls for cockpit crew to don oxygen masks and establish crew communication. Pressurization panel switched to alternate and manual to close outflow valve without success. Cabin continues to climb. First officer directed to QRH for 'loss of pressurization' checklist while captain requests lower altitude from ARTCC for pressurization problem. At 14000 ft MSL, the passenger oxygen light illuminates indicating oxygen masks in cabin deployed. Captain requests return to den and further descent. In turn, captain discovers bleeds/packs left in takeoff confign. Never reconfigured during climb checklist after flap retraction. First officer missed climb checklist item 'bleeds/packs configured.' APU secured without checking bleeds/pack confign. After horn sounded, both crew members missed bleeds/packs in wrong position, crew focused on pressurization panel. Crew failed to discover incorrect bleeds/packs until after masks deployed. Human factors include some fatigue after 3 1/2 hour layover. First officer commutes from detroit to denver and had previously shown poor performance at the late stages of the day. Recommend commute day prior to trips. Physical factors: dark night, overhead panel lit dimly. Thunderstorms and avoidance a concern and occupied time. Supplemental information from acn 403145: company policy states that all takeoffs out of denver are done with engine bleeds off. At 1000 ft MSL, the captain called for the 'flap up, climb checklist.' as I did in the past, I executed the check by a flow pattern first. While doing that, we were told by tower to switch over to departure control. This caused me to stop in the middle of doing my check in order to respond to the tower controller and call departure control. By the time I was done talking to departure control, we were at 10000 ft, the altitude when I normally call the company to return the departure times. On the way back to denver, the captain noticed that the engine bleeds were not reset to the 'on' position, indicating that the cabin never pressurized. I then realized that I did not finish the climb checklist because resetting the engine bleeds to 'on' position is an item on the climb checklist. (Indicated on the checklist as engine bleeds -- check.) we then returned with a normal landing at denver. Because the passenger oxygen system was used and cockpit oxygen was used, the aircraft was grounded. We switched planes and completed the flight to san francisco. Because I allowed myself to get caught up in doing the radios and possibly fatigue, I think is the reason I forgot to finish the checklist. In other words, poor radio and checklist management.

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Original NASA ASRS Text

Title: A B737-300 FLC EXPERIENCES A LOSS OF CABIN PRESSURE CLBING THROUGH FL190. THE FO HAD FORGOTTEN TO TURN ON THE ENG BLEED AIR FOR THE CABIN PRESSURIZATION SYS.

Narrative: ACFT DEPARTED DEN ON NIGHT FLT TO SFO. TKOF WAS CONDUCTED IN SOP BLEEDS OFF TKOF CONFIGN. WX WAS A CONCERN WITH TSTMS ON COURSE SO RADAR WAS TUNED FOR TSTM AVOIDANCE. CAPT (PF) HANDLED FLYING AND ATC COM WHILE FO LEFT PRIMARY FREQ TO CALL COMPANY WITH OUTBOUND CALL ON RADIO #2. PRIOR TO LEAVING FREQ, NOW AT ABOUT 10000 FT MSL, FO SECURES APU. AROUND 15000 FT MSL, FO RPTS BACK ON RADIO #1 AFTER CALLING COMPANY. ABOUT FL200, THE CABIN ALT WARNING HORN SOUNDS. FO SILENCES HORN, CREW DISCOVERS CABIN ALT AT 10000 FT MSL AND CLBING. ALL CAUTION AND WARNING LIGHTS ARE NOT ILLUMINATED. CAPT CALLS FOR COCKPIT CREW TO DON OXYGEN MASKS AND ESTABLISH CREW COM. PRESSURIZATION PANEL SWITCHED TO ALTERNATE AND MANUAL TO CLOSE OUTFLOW VALVE WITHOUT SUCCESS. CABIN CONTINUES TO CLB. FO DIRECTED TO QRH FOR 'LOSS OF PRESSURIZATION' CHKLIST WHILE CAPT REQUESTS LOWER ALT FROM ARTCC FOR PRESSURIZATION PROB. AT 14000 FT MSL, THE PAX OXYGEN LIGHT ILLUMINATES INDICATING OXYGEN MASKS IN CABIN DEPLOYED. CAPT REQUESTS RETURN TO DEN AND FURTHER DSCNT. IN TURN, CAPT DISCOVERS BLEEDS/PACKS LEFT IN TKOF CONFIGN. NEVER RECONFIGURED DURING CLB CHKLIST AFTER FLAP RETRACTION. FO MISSED CLB CHKLIST ITEM 'BLEEDS/PACKS CONFIGURED.' APU SECURED WITHOUT CHKING BLEEDS/PACK CONFIGN. AFTER HORN SOUNDED, BOTH CREW MEMBERS MISSED BLEEDS/PACKS IN WRONG POS, CREW FOCUSED ON PRESSURIZATION PANEL. CREW FAILED TO DISCOVER INCORRECT BLEEDS/PACKS UNTIL AFTER MASKS DEPLOYED. HUMAN FACTORS INCLUDE SOME FATIGUE AFTER 3 1/2 HR LAYOVER. FO COMMUTES FROM DETROIT TO DENVER AND HAD PREVIOUSLY SHOWN POOR PERFORMANCE AT THE LATE STAGES OF THE DAY. RECOMMEND COMMUTE DAY PRIOR TO TRIPS. PHYSICAL FACTORS: DARK NIGHT, OVERHEAD PANEL LIT DIMLY. TSTMS AND AVOIDANCE A CONCERN AND OCCUPIED TIME. SUPPLEMENTAL INFO FROM ACN 403145: COMPANY POLICY STATES THAT ALL TKOFS OUT OF DENVER ARE DONE WITH ENG BLEEDS OFF. AT 1000 FT MSL, THE CAPT CALLED FOR THE 'FLAP UP, CLB CHKLIST.' AS I DID IN THE PAST, I EXECUTED THE CHK BY A FLOW PATTERN FIRST. WHILE DOING THAT, WE WERE TOLD BY TWR TO SWITCH OVER TO DEP CTL. THIS CAUSED ME TO STOP IN THE MIDDLE OF DOING MY CHK IN ORDER TO RESPOND TO THE TWR CTLR AND CALL DEP CTL. BY THE TIME I WAS DONE TALKING TO DEP CTL, WE WERE AT 10000 FT, THE ALT WHEN I NORMALLY CALL THE COMPANY TO RETURN THE DEP TIMES. ON THE WAY BACK TO DENVER, THE CAPT NOTICED THAT THE ENG BLEEDS WERE NOT RESET TO THE 'ON' POS, INDICATING THAT THE CABIN NEVER PRESSURIZED. I THEN REALIZED THAT I DID NOT FINISH THE CLB CHKLIST BECAUSE RESETTING THE ENG BLEEDS TO 'ON' POS IS AN ITEM ON THE CLB CHKLIST. (INDICATED ON THE CHKLIST AS ENG BLEEDS -- CHK.) WE THEN RETURNED WITH A NORMAL LNDG AT DENVER. BECAUSE THE PAX OXYGEN SYS WAS USED AND COCKPIT OXYGEN WAS USED, THE ACFT WAS GNDED. WE SWITCHED PLANES AND COMPLETED THE FLT TO SAN FRANCISCO. BECAUSE I ALLOWED MYSELF TO GET CAUGHT UP IN DOING THE RADIOS AND POSSIBLY FATIGUE, I THINK IS THE REASON I FORGOT TO FINISH THE CHKLIST. IN OTHER WORDS, POOR RADIO AND CHKLIST MGMNT.

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.