Narrative:

Our day started out uneventfully. The entire crew overnighted at the same hotel and we reported to the aircraft on time if not early. The captain was waiting for his wife to clear security; so I proceeded to the gate and I told him I'd get everything ready to go. I got to the aircraft and completed the first flight of the day checks; checked the logbook and entered our flight information into it. I swapped the data base in the FMC; re-aligned and put in the present position in the FMC. I initialized the ACARS and uploaded the flight plan. I then proceeded to do an exterior walk around. Upon completion I returned to the cockpit and finished setting up for the flight. I did the overhead; set the cruise and landing altitudes. I then got the current ATIS and requested the pre departure clearance. Upon receipt of the pre departure clearance I loaded the departure and arrivals; checked the notams and weather. At about 20-25 minutes before push the captain arrived and passed out coffee for the crew. I informed him that everything had been done and that we were ready to go upon the completion of boarding. At that point I was supposed to have been pilot not flying and it was the captain's leg. He said since I'd done everything I might as well fly this leg; I agreed. Boarding was completed early and was uneventful. We pushed back from the gate and had a normal engine start of the right engine. We taxied out and were #4 for takeoff approximately 10 minutes before curfew being lifted for departures. I did the delayed start check and started the left engine. We completed the delayed start checklist and before take off checklist. Take off roll was normal and initial climbout. At 1;000 ft I called for VNAV. Right at the time I called for flaps up; we received a call from tower to switch to departure. This interrupted my train of thought; and I don't recall if I called for the after takeoff checklist. I usually call out 'flaps up/after takeoff checklist.' I remained hand flying the aircraft and upon switching to departure control we were given a climb to FL230. The captain responded to ATC climb 230 unrestricted. I then asked him if we were still speed restricted to 230 KTS (SID restriction) or if I could speed up to 250 KTS. It was a distraction and may have contributed to the failure to do the after takeoff checklist. Also about the same time we had turned into the sun and were again distracted by putting on sunglasses. I turned on the autopilot around 10;000 ft and the aircraft started to accelerate to climb speed. I think we were accelerating through around 300 KTS when ATC gave us a speed restriction of 270 KTS. I opened the speed window and dialed in 270. I noted the climb rate was exceeding 3;500 FPM and noted that the autopilot over compensated with a near level off when reaching 270. Shortly thereafter is when the intermittent warning horn went off. Both myself and the captain looked for obvious causes. What stood out was that the gear handle was still in the up and on position. The captain put the gear handle in the off position and the warning horn continued to sound. The elapsed time was about 5 seconds. With the warning horn continuing to sound I called for oxygen masks to be donned. We established communications; however it was labored and we had to shout at each other as the interphone wasn't working. At that point the captain directed me to descend to 10;000 ft; that I had the aircraft and radios and he began to run the QRH checklist and coordinate with the flight attendants. I declared an emergency with ATC and requested a descent to 10;000 ft and heading to clear terrain. I had had terrain mode selected for the departure; however after donning the oxygen mask it began to fog up and my vision was deteriorating. Rather than try and operate the MCP with limited vision I opted to hand fly the aircraft. Upon reaching 10;000 ft we were able to remove the oxygen masks. The captain was very busy trying to complete the checklist and coordinate with the cabin. I requested vectors back and began to prepare for the approach. At some point; I don't recall when I glanced up at the overhead and noticed both bleed trips illuminated. Instinctively I reached up and hit the trip reset switch. I cannot recall if I did this before or after the captain selected the cabin controller to manual and closed the outflow valve. In hindsight I should not have pushed the bleed trip reset as the captain was running the checklist. In my mind I saw that both bleeds were on but that they had tripped. I thought that if they'd reset then we could get air to the packs and pressurize. Again; I should have let the captain complete the QRH. We were cleared for the approach when the captain completed the QRH. As we were very close to landing the captain requested delay vectors to complete the descent and approach checklists and make sure we were completely ready for landing. Once we were ready to continue the approach we were given a turn to final and cleared for a visual. I had backed up the approach with the localizer and was using LNAV/VNAV guidance. Somewhere inside the final approach fix the flight attendant called up that there was smoke in the aft cabin. While the captain was coordinating with the flight attendant with this new issue I asked ATC to roll crash fire rescue equipment as we had smoke in the cabin. Landing and rollout were normal and we exited the high speed and came to a stop. Due to the report of smoke in the cabin the captain directed me to shut down both engines. I continued to monitor ATC and crash fire rescue equipment on the radio while the captain talked with the flight attendant. Upon landing the smoke dissipated and there was no smell or visible smoke. However the cabin smoke detectors had activated and continued until reset by the lead flight attendant. The aircraft was powered by the APU electrical but the APU bleed was left off. Upon release by crash fire rescue equipment we were towed to the gate by company operations.six passengers were treated by emt's at the gate for sore ears; one of which was transported to the hospital. After we got to the gate and completed the shutdown checklist and deplaned the passengers I noticed that the printer had printed out an ACARS message at around 7;500 ft warning of a potential pressurization problem and to check the bleeds on. Neither myself nor the captain remember hearing an ACARS tone alerting us of a message nor did either of us notice the message until after we were at the gate. I did not know that the bleed switches were in the off position until after the captain and I discussed probable causes. I told him I'd seen the switches in the on position when I noticed the bleed trip off lights illuminated. At that point he told me that he'd positioned them on when driven to by the QRH. That's when I realized that this event was pilot induced by a failure to complete checklist items and verify switch positions. Pilot actions that could have prevented this; I didn't realize it at the time; but I was task saturated by completing all the fly and non-fly preflight duties. Had I been doing just the non-fly duties I would have had more time to pay attention to detail; having said that; there were numerous places in subsequent checklists that would have prevented this event. Adherence to checklist discipline and switch verification with tactile touch would prevented this from happening. Another pilot action to prevent this from happening would be to place your hand on each switch as you are verifying its' position. Our minds tend to see what we think we should see a tactile touch would reduce this tendency to error. When I am the pilot not flying and doing the after takeoff checklist I physically place my left hand up to the cabin altitude window and rate of climb window and put a finger on each gauge to verify pressurization. I've been doing that ever since I've read previous reports of similar incidents and assured myself that I'd never be in this position. I could have done that as pilot flying as well. Another pilot action that may have prevented this is use of automation sooner rather than hand flying the entire SID or up to 10;000 ft. By doing so I would have been back in the loop sooner. Also I could have worn my sunglasses on takeoff roll instead of trying to put them on in a climbing turn into the sun. Other group action that could be taken to prevent this from occurring again: the engine bleed switches are not on the shutdown or securing checklist. A mandatory safety bulletin prohibiting turning the switches off should be issued. A change to the preflight checklist could also be incorporated to state: engine bleed switches on. I realize it's in the expanded vol 1 preflight procedures but as I can see now; it's being missed. Also a safety bulletin and directive to maintenance should be issued to not turn the engine bleeds off and if a maintenance procedure requires it then the procedures should be changed to include a step to turn them back on. Despite multiple checklist mistakes by myself and the captain as well as the failure to complete the after take off checklist; this event would not have happened had someone not turned the engine bleeds off when they should not have. There were contributing factors in the chain of events. Complacency; task saturation and checklist/switch verification all contributed to this event.

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Original NASA ASRS Text

Title: B737 First Officer describes the events leading up to a cabin altitude warning horn on climbout and the subsequent return to the departure airport.

Narrative: Our day started out uneventfully. The entire crew overnighted at the same hotel and we reported to the aircraft on time if not early. The Captain was waiting for his wife to clear security; so I proceeded to the gate and I told him I'd get everything ready to go. I got to the aircraft and completed the first flight of the day checks; checked the logbook and entered our flight information into it. I swapped the data base in the FMC; re-aligned and put in the present position in the FMC. I initialized the ACARS and uploaded the flight plan. I then proceeded to do an exterior walk around. Upon completion I returned to the cockpit and finished setting up for the flight. I did the overhead; set the cruise and landing altitudes. I then got the current ATIS and requested the PDC. Upon receipt of the PDC I loaded the departure and arrivals; checked the NOTAMs and weather. At about 20-25 minutes before push the Captain arrived and passed out coffee for the crew. I informed him that everything had been done and that we were ready to go upon the completion of boarding. At that point I was supposed to have been pilot not flying and it was the Captain's leg. He said since I'd done everything I might as well fly this leg; I agreed. Boarding was completed early and was uneventful. We pushed back from the gate and had a normal engine start of the right engine. We taxied out and were #4 for takeoff approximately 10 minutes before curfew being lifted for departures. I did the delayed start check and started the left engine. We completed the delayed start checklist and before take off checklist. Take off roll was normal and initial climbout. At 1;000 FT I called for VNAV. Right at the time I called for flaps up; we received a call from Tower to switch to Departure. This interrupted my train of thought; and I don't recall if I called for the After Takeoff Checklist. I usually call out 'flaps up/after takeoff checklist.' I remained hand flying the aircraft and upon switching to Departure Control we were given a climb to FL230. The Captain responded to ATC climb 230 unrestricted. I then asked him if we were still speed restricted to 230 KTS (SID restriction) or if I could speed up to 250 KTS. It was a distraction and may have contributed to the failure to do the After Takeoff Checklist. Also about the same time we had turned into the sun and were again distracted by putting on sunglasses. I turned on the autopilot around 10;000 FT and the aircraft started to accelerate to climb speed. I think we were accelerating through around 300 KTS when ATC gave us a speed restriction of 270 KTS. I opened the speed window and dialed in 270. I noted the climb rate was exceeding 3;500 FPM and noted that the autopilot over compensated with a near level off when reaching 270. Shortly thereafter is when the Intermittent warning horn went off. Both myself and the Captain looked for obvious causes. What stood out was that the gear handle was still in the up and on position. The Captain put the gear handle in the off position and the warning horn continued to sound. The elapsed time was about 5 seconds. With the warning horn continuing to sound I called for oxygen masks to be donned. We established communications; however it was labored and we had to shout at each other as the interphone wasn't working. At that point the Captain directed me to descend to 10;000 FT; that I had the aircraft and radios and he began to run the QRH checklist and coordinate with the flight attendants. I declared an emergency with ATC and requested a descent to 10;000 FT and heading to clear terrain. I had had terrain mode selected for the departure; however after donning the oxygen mask it began to fog up and my vision was deteriorating. Rather than try and operate the MCP with limited vision I opted to hand fly the aircraft. Upon reaching 10;000 FT we were able to remove the oxygen masks. The Captain was very busy trying to complete the checklist and coordinate with the cabin. I requested vectors back and began to prepare for the approach. At some point; I don't recall when I glanced up at the overhead and noticed both Bleed Trips illuminated. Instinctively I reached up and hit the trip reset switch. I cannot recall if I did this before or after the Captain selected the Cabin Controller to manual and closed the outflow valve. In hindsight I should not have pushed the bleed trip reset as the Captain was running the checklist. In my mind I saw that both bleeds were on but that they had tripped. I thought that if they'd reset then we could get air to the packs and pressurize. Again; I should have let the Captain complete the QRH. We were cleared for the approach when the Captain completed the QRH. As we were very close to landing the Captain requested delay vectors to complete the Descent and Approach checklists and make sure we were completely ready for landing. Once we were ready to continue the approach we were given a turn to final and cleared for a visual. I had backed up the approach with the localizer and was using LNAV/VNAV guidance. Somewhere inside the final approach fix the Flight Attendant called up that there was smoke in the AFT cabin. While the Captain was coordinating with the Flight Attendant with this new issue I asked ATC to roll CFR as we had smoke in the cabin. Landing and rollout were normal and we exited the high speed and came to a stop. Due to the report of smoke in the cabin the Captain directed me to shut down both engines. I continued to monitor ATC and CFR on the radio while the Captain talked with the Flight Attendant. Upon landing the smoke dissipated and there was no smell or visible smoke. However the cabin smoke detectors had activated and continued until reset by the Lead Flight Attendant. The aircraft was powered by the APU electrical but the APU bleed was left off. Upon release by CFR we were towed to the gate by company operations.Six passengers were treated by EMT's at the gate for sore ears; one of which was transported to the hospital. After we got to the gate and completed the shutdown checklist and deplaned the passengers I noticed that the printer had printed out an ACARS message at around 7;500 FT warning of a potential pressurization problem and to check the bleeds on. Neither myself nor the Captain remember hearing an ACARS tone alerting us of a message nor did either of us notice the message until after we were at the gate. I did not know that the Bleed switches were in the off position until after the Captain and I discussed probable causes. I told him I'd seen the switches in the ON position when I noticed the Bleed Trip off lights illuminated. At that point he told me that he'd positioned them on when driven to by the QRH. That's when I realized that this event was pilot induced by a failure to complete checklist items and verify switch positions. Pilot actions that could have prevented this; I didn't realize it at the time; but I was task saturated by completing all the fly and non-fly preflight duties. Had I been doing just the non-fly duties I would have had more time to pay attention to detail; having said that; there were numerous places in subsequent checklists that would have prevented this event. Adherence to checklist discipline and switch verification with tactile touch would prevented this from happening. Another pilot action to prevent this from happening would be to place your hand on each switch as you are verifying its' position. Our minds tend to see what we think we should see a tactile touch would reduce this tendency to error. When I am the pilot not flying and doing the After Takeoff Checklist I physically place my left hand up to the cabin altitude window and rate of climb window and put a finger on each gauge to verify pressurization. I've been doing that ever since I've read previous reports of similar incidents and assured myself that I'd never be in this position. I could have done that as pilot flying as well. Another pilot action that may have prevented this is use of automation sooner rather than hand flying the entire SID or up to 10;000 FT. By doing so I would have been back in the loop sooner. Also I could have worn my sunglasses on takeoff roll instead of trying to put them on in a climbing turn into the sun. Other Group Action that could be taken to prevent this from occurring again: The Engine Bleed switches are NOT on the Shutdown or Securing Checklist. A mandatory Safety Bulletin prohibiting turning the switches off should be issued. A change to the preflight checklist could also be incorporated to state: Engine Bleed Switches ON. I realize it's in the expanded Vol 1 preflight procedures but as I can see now; it's being missed. Also a Safety bulletin and directive to Maintenance should be issued to NOT turn the engine bleeds off and if a maintenance procedure requires it then the procedures should be changed to include a step to turn them back ON. Despite multiple checklist mistakes by myself and the Captain as well as the failure to complete the after take off checklist; this event would NOT have happened had someone not turned the Engine bleeds OFF when they should not have. There were contributing factors in the chain of events. Complacency; task saturation and checklist/switch verification all contributed to this event.

Data retrieved from NASA's ASRS site 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.