Narrative:

The flight originated without incident until the aircraft passed through 11500 ft. It was at this time the cabin altitude warning came on. Upon running the appropriate checklists it was discovered that the air conditioning packs were set in the wrong position. I do not believe this was a procedural problem. I was in a hurry doing several things at once. When performing the taxi, takeoff, and after takeoff checklists, the position of the air conditioning pack switches appeared to be in the correct position. The problem could have been discovered earlier if the pressurization indicator had a different design. The after takeoff checklist requires consulting the pressurization indicator. When I did this, the pressurization differential looked normal. In addition, I felt unusual pressure changes in my ears which made me again consult the pressure indicator. As it turns out, what I was looking at was the cabin altitude, not the pressurization differential. Both of these quantities are read from the same numbers on the same gauge. So when I saw what I thought was a pressure differential of 1.5 psi, what I was really looking at was a cabin altitude of 1500 ft. It wasn't until the cabin altitude alarm went off that I realized that I was looking at the wrong needle. As soon as I realized this, I knew what the problem was. Supplemental information from acn 460519: through the execution of this checklist we discovered the first officer had forgotten to turn on the air conditioning/pressurization packs, and as a result the cabin had not pressurized. At the time of the alert, I was hand flying the aircraft in night, IFR conditions with ice and rain visible. Because I was hand flying I did not have the opportunity to watch the first officer's actual completion of the after takeoff flow and checklist. The time between 10000 ft and 11500 ft when we received the alarm was very busy. The first officer had 6 opportunities to correct the problem -- 3 flows and 3 separate checklists (pre taxi, before takeoff and after takeoff). This could have been prevented, and should be corrected by giving the first officer more training in the proper use of flows and checklists, with attention to switch placement.

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Original NASA ASRS Text

Title: AN EMB120 FO FAILS TO SET THE CABIN PRESSURIZATION CORRECTLY, MISREADS THE DIAL AND ALLOWS THE CABIN PRESSURE TO SET OFF THE CABIN ALT WARNING ALERT. ZOA, CA.

Narrative: THE FLT ORIGINATED WITHOUT INCIDENT UNTIL THE ACFT PASSED THROUGH 11500 FT. IT WAS AT THIS TIME THE CABIN ALT WARNING CAME ON. UPON RUNNING THE APPROPRIATE CHKLISTS IT WAS DISCOVERED THAT THE AIR CONDITIONING PACKS WERE SET IN THE WRONG POS. I DO NOT BELIEVE THIS WAS A PROCEDURAL PROB. I WAS IN A HURRY DOING SEVERAL THINGS AT ONCE. WHEN PERFORMING THE TAXI, TKOF, AND AFTER TKOF CHKLISTS, THE POS OF THE AIR CONDITIONING PACK SWITCHES APPEARED TO BE IN THE CORRECT POS. THE PROB COULD HAVE BEEN DISCOVERED EARLIER IF THE PRESSURIZATION INDICATOR HAD A DIFFERENT DESIGN. THE AFTER TKOF CHKLIST REQUIRES CONSULTING THE PRESSURIZATION INDICATOR. WHEN I DID THIS, THE PRESSURIZATION DIFFERENTIAL LOOKED NORMAL. IN ADDITION, I FELT UNUSUAL PRESSURE CHANGES IN MY EARS WHICH MADE ME AGAIN CONSULT THE PRESSURE INDICATOR. AS IT TURNS OUT, WHAT I WAS LOOKING AT WAS THE CABIN ALT, NOT THE PRESSURIZATION DIFFERENTIAL. BOTH OF THESE QUANTITIES ARE READ FROM THE SAME NUMBERS ON THE SAME GAUGE. SO WHEN I SAW WHAT I THOUGHT WAS A PRESSURE DIFFERENTIAL OF 1.5 PSI, WHAT I WAS REALLY LOOKING AT WAS A CABIN ALT OF 1500 FT. IT WASN'T UNTIL THE CABIN ALT ALARM WENT OFF THAT I REALIZED THAT I WAS LOOKING AT THE WRONG NEEDLE. AS SOON AS I REALIZED THIS, I KNEW WHAT THE PROB WAS. SUPPLEMENTAL INFO FROM ACN 460519: THROUGH THE EXECUTION OF THIS CHKLIST WE DISCOVERED THE FO HAD FORGOTTEN TO TURN ON THE AIR CONDITIONING/PRESSURIZATION PACKS, AND AS A RESULT THE CABIN HAD NOT PRESSURIZED. AT THE TIME OF THE ALERT, I WAS HAND FLYING THE ACFT IN NIGHT, IFR CONDITIONS WITH ICE AND RAIN VISIBLE. BECAUSE I WAS HAND FLYING I DID NOT HAVE THE OPPORTUNITY TO WATCH THE FO'S ACTUAL COMPLETION OF THE AFTER TKOF FLOW AND CHKLIST. THE TIME BTWN 10000 FT AND 11500 FT WHEN WE RECEIVED THE ALARM WAS VERY BUSY. THE FO HAD 6 OPPORTUNITIES TO CORRECT THE PROB -- 3 FLOWS AND 3 SEPARATE CHKLISTS (PRE TAXI, BEFORE TKOF AND AFTER TKOF). THIS COULD HAVE BEEN PREVENTED, AND SHOULD BE CORRECTED BY GIVING THE FO MORE TRAINING IN THE PROPER USE OF FLOWS AND CHKLISTS, WITH ATTN TO SWITCH PLACEMENT.

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.