Narrative:

We departed den going to ict. We had done an engine bleeds off takeoff, so the APU was used to pressurize the airplane for takeoff. At cruise, I looked up and the APU was still on, so I turned it off not seeing that it was still being used to pressurize the airplane. The horn went on when the cabin altitude reached 10000 ft but it is the same horn for the takeoff warning. So at first we thought it was a takeoff warning horn. Just as the cabin reached 14000 ft MSL, we caught the problems and restored the cabin pressure. The passenger oxygen mask did drop, but no emergency descent was needed. There was no emergency declared. All the checklists were completed. No injuries or complaints were known.

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Original NASA ASRS Text

Title: CAPT OF AN MLG ACR ACFT INADVERTENTLY TURNED OFF THE ACFT PRESSURIZATION WHEN SHUTTING DOWN THE APU IN CRUISE RESULTING IN ALL PAX OXYGEN MASKS DROPPING FOR USE.

Narrative: WE DEPARTED DEN GOING TO ICT. WE HAD DONE AN ENG BLEEDS OFF TKOF, SO THE APU WAS USED TO PRESSURIZE THE AIRPLANE FOR TKOF. AT CRUISE, I LOOKED UP AND THE APU WAS STILL ON, SO I TURNED IT OFF NOT SEEING THAT IT WAS STILL BEING USED TO PRESSURIZE THE AIRPLANE. THE HORN WENT ON WHEN THE CABIN ALT REACHED 10000 FT BUT IT IS THE SAME HORN FOR THE TKOF WARNING. SO AT FIRST WE THOUGHT IT WAS A TKOF WARNING HORN. JUST AS THE CABIN REACHED 14000 FT MSL, WE CAUGHT THE PROBS AND RESTORED THE CABIN PRESSURE. THE PAX OXYGEN MASK DID DROP, BUT NO EMER DSCNT WAS NEEDED. THERE WAS NO EMER DECLARED. ALL THE CHKLISTS WERE COMPLETED. NO INJURIES OR COMPLAINTS WERE KNOWN.

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.