Narrative:

He had just taken off from rno and were on a vector to intercept the lovelock 208 degree radial. We had an inoperative APU and had made a packs off takeoff in accordance with the flight manual. After power reduction after takeoff, the packs were turned on and pressurization controller was set to automatic in accordance with flight manual procedures. The cabin began to pressurize and climb out appeared normal. Passing approximately 12500 ft an intermittent warning horn came on. We suspected the horn was caused by a problem with the air/ground switch on the gear and began to troubleshoot. We checked the gear (went from off to up with the gear handle), flap annunciators, and cycled speed brakes in its detent. The captain pulled out the handbook to reconfirm the items on the takeoff warning system. We continued our climb and passing 15500 ft we got an overhead annunciator light and passenger oxygen light. At the time we noticed the cabin altitude was between 14000-15000 ft . We also had the pressurization controller 'standby' mode light on with the mode switch in automatic. The cabin rate of climb was still climbing and the captain cycled the controller from automatic to standby back to automatic and then back to standby. We regained control of the pressurization. We requested clearance back down to 10000 ft when we got the passenger oxygen light and regained pressurization control in a descent passing about 14000 ft headed for 10000. The passenger oxygen masks deployed when the cabin exceeded 14000 ft. I feel we could have prevented the masks from deploying had we recognized the horn was a pressurization and not an air/ground switch problem. Both problems use the same warning horn. Neither of us noticed any problems with our ears when the cabin was not pressurizing. We both felt this would be one of your first clues of a pressurization problem.

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Original NASA ASRS Text

Title: ACR MLG ACFT RETURNED TO LAND AFTER THE ACFT CABIN PRESSURIZATION FAILED AND ALL PAX OXYGEN MASKS DROPPED DOWN FOR USE.

Narrative: HE HAD JUST TAKEN OFF FROM RNO AND WERE ON A VECTOR TO INTERCEPT THE LOVELOCK 208 DEG RADIAL. WE HAD AN INOP APU AND HAD MADE A PACKS OFF TKOF IAW THE FLT MANUAL. AFTER PWR REDUCTION AFTER TKOF, THE PACKS WERE TURNED ON AND PRESSURIZATION CTLR WAS SET TO AUTO IAW FLT MANUAL PROCS. THE CABIN BEGAN TO PRESSURIZE AND CLBOUT APPEARED NORMAL. PASSING APPROX 12500 FT AN INTERMITTENT WARNING HORN CAME ON. WE SUSPECTED THE HORN WAS CAUSED BY A PROBLEM WITH THE AIR/GND SWITCH ON THE GEAR AND BEGAN TO TROUBLESHOOT. WE CHKED THE GEAR (WENT FROM OFF TO UP WITH THE GEAR HANDLE), FLAP ANNUNCIATORS, AND CYCLED SPD BRAKES IN ITS DETENT. THE CAPT PULLED OUT THE HANDBOOK TO RECONFIRM THE ITEMS ON THE TKOF WARNING SYS. WE CONTINUED OUR CLB AND PASSING 15500 FT WE GOT AN OVERHEAD ANNUNCIATOR LIGHT AND PAX OXYGEN LIGHT. AT THE TIME WE NOTICED THE CABIN ALT WAS BTWN 14000-15000 FT . WE ALSO HAD THE PRESSURIZATION CTLR 'STANDBY' MODE LIGHT ON WITH THE MODE SWITCH IN AUTO. THE CABIN RATE OF CLB WAS STILL CLBING AND THE CAPT CYCLED THE CTLR FROM AUTO TO STANDBY BACK TO AUTO AND THEN BACK TO STANDBY. WE REGAINED CTL OF THE PRESSURIZATION. WE REQUESTED CLRNC BACK DOWN TO 10000 FT WHEN WE GOT THE PAX OXYGEN LIGHT AND REGAINED PRESSURIZATION CTL IN A DSCNT PASSING ABOUT 14000 FT HEADED FOR 10000. THE PAX OXYGEN MASKS DEPLOYED WHEN THE CABIN EXCEEDED 14000 FT. I FEEL WE COULD HAVE PREVENTED THE MASKS FROM DEPLOYING HAD WE RECOGNIZED THE HORN WAS A PRESSURIZATION AND NOT AN AIR/GND SWITCH PROBLEM. BOTH PROBLEMS USE THE SAME WARNING HORN. NEITHER OF US NOTICED ANY PROBLEMS WITH OUR EARS WHEN THE CABIN WAS NOT PRESSURIZING. WE BOTH FELT THIS WOULD BE ONE OF YOUR FIRST CLUES OF A PRESSURIZATION PROBLEM.

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.