Narrative:

A charter flight from atlantic city to detroit. Aircraft was large transport type. Preflight through takeoff was normal. I, as first officer, was flying this leg. Climb out was normal except for a hold at lower altitudes for conflicting traffic going into and out of philly. Approximately 15 min into the flight we were cleared to our cruising altitude of FL310. About 20 min into flight climbing our of FL230 the second officer said that the cabin was starting to climb at an abnormal rate. This was also felt by the rest of the crew.I leveled off at FL240 while the captain and second officer completed the stabilizing actions for loss of pressurization. After about 30 seconds at FL240 I donned my oxy mask as a precaution and requested a lower altitude to the captain. He coordination lower and I started down, about 1 to 1 1/2 min after pressurization started to be lost. As I started out of FL225 the second officer said he could not control cabin pressure and that the manual mode wasn't working either and the cabin was now increasing at 6000'/min. We had clearance to 12000' and I started a rapid descent 6000' plus to that altitude as the captain requested 10000' from center. We had been on vector during climb and continued vectors from center during descent. Center was fully cooperative and assisted us in every aspect they could. Passing 14000' the cabin altitude horn went off and passenger oxy deployed. The system worked normally. The second officer said that he was gaining control of the cabin slowly as we passed 13000'. We leveled off at 10000' and the second officer continued bring down the bacin to landing altitude. After assessing no one was hurt and fuel and aircraft were ok we continued on and landed west/O further incident at dtw. This problem of lost pressurization was of unknown causes from the standpoint of the second officer. Looking into the pressurization system a problem arises that to get the outflow valves full open you have to exceed 9.42 psi cabin differential. However the second officer said he had set the cabin to 3000 giving adequate margin at FL230 with pressurization controls set normally. So either the pressure controller malfunctioned or operator error existed. We gained control of the pressurization at 13000' and remained in control for remainder of flight. So that rules out controller failure. What caused the error to happen. The second officer could have set the cabin rate of climb to 0'/min or he could have put on only one air conditioning pack to provide air. Talking through the problem after landing the second officer said he remembers the cabin climbing early into flight. Being vectored for traffic maybe he was distraction from checking cabin altitude performance while looking for other aircraft while climbing out to cruise altitude. This could not be confirmed by second officer. As to the pack being off the captain checked them during stabilization steps taken. Probable cause was operator error of unknown switch positioning in pressurization system.

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Original NASA ASRS Text

Title: LOSS OF CABIN PRESSURIZATION RESULTS IN EMERGENCY DESCENT TO 10000'.

Narrative: A CHARTER FLT FROM ATLANTIC CITY TO DETROIT. ACFT WAS LGT TYPE. PREFLT THROUGH TKOF WAS NORMAL. I, AS F/O, WAS FLYING THIS LEG. CLB OUT WAS NORMAL EXCEPT FOR A HOLD AT LOWER ALTS FOR CONFLICTING TFC GOING INTO AND OUT OF PHILLY. APPROX 15 MIN INTO THE FLT WE WERE CLRED TO OUR CRUISING ALT OF FL310. ABOUT 20 MIN INTO FLT CLBING OUR OF FL230 THE S/O SAID THAT THE CABIN WAS STARTING TO CLB AT AN ABNORMAL RATE. THIS WAS ALSO FELT BY THE REST OF THE CREW.I LEVELED OFF AT FL240 WHILE THE CAPT AND S/O COMPLETED THE STABILIZING ACTIONS FOR LOSS OF PRESSURIZATION. AFTER ABOUT 30 SECS AT FL240 I DONNED MY OXY MASK AS A PRECAUTION AND REQUESTED A LOWER ALT TO THE CAPT. HE COORD LOWER AND I STARTED DOWN, ABOUT 1 TO 1 1/2 MIN AFTER PRESSURIZATION STARTED TO BE LOST. AS I STARTED OUT OF FL225 THE S/O SAID HE COULD NOT CTL CABIN PRESSURE AND THAT THE MANUAL MODE WASN'T WORKING EITHER AND THE CABIN WAS NOW INCREASING AT 6000'/MIN. WE HAD CLRNC TO 12000' AND I STARTED A RAPID DSNT 6000' PLUS TO THAT ALT AS THE CAPT REQUESTED 10000' FROM CTR. WE HAD BEEN ON VECTOR DURING CLB AND CONTINUED VECTORS FROM CTR DURING DSNT. CTR WAS FULLY COOPERATIVE AND ASSISTED US IN EVERY ASPECT THEY COULD. PASSING 14000' THE CABIN ALT HORN WENT OFF AND PAX OXY DEPLOYED. THE SYS WORKED NORMALLY. THE S/O SAID THAT HE WAS GAINING CTL OF THE CABIN SLOWLY AS WE PASSED 13000'. WE LEVELED OFF AT 10000' AND THE S/O CONTINUED BRING DOWN THE BACIN TO LNDG ALT. AFTER ASSESSING NO ONE WAS HURT AND FUEL AND ACFT WERE OK WE CONTINUED ON AND LANDED W/O FURTHER INCIDENT AT DTW. THIS PROB OF LOST PRESSURIZATION WAS OF UNKNOWN CAUSES FROM THE STANDPOINT OF THE S/O. LOOKING INTO THE PRESSURIZATION SYS A PROB ARISES THAT TO GET THE OUTFLOW VALVES FULL OPEN YOU HAVE TO EXCEED 9.42 PSI CABIN DIFFERENTIAL. HOWEVER THE S/O SAID HE HAD SET THE CABIN TO 3000 GIVING ADEQUATE MARGIN AT FL230 WITH PRESSURIZATION CTLS SET NORMALLY. SO EITHER THE PRESSURE CTLR MALFUNCTIONED OR OPERATOR ERROR EXISTED. WE GAINED CTL OF THE PRESSURIZATION AT 13000' AND REMAINED IN CTL FOR REMAINDER OF FLT. SO THAT RULES OUT CTLR FAILURE. WHAT CAUSED THE ERROR TO HAPPEN. THE S/O COULD HAVE SET THE CABIN RATE OF CLB TO 0'/MIN OR HE COULD HAVE PUT ON ONLY ONE AIR CONDITIONING PACK TO PROVIDE AIR. TALKING THROUGH THE PROB AFTER LNDG THE S/O SAID HE REMEMBERS THE CABIN CLBING EARLY INTO FLT. BEING VECTORED FOR TFC MAYBE HE WAS DISTR FROM CHKING CABIN ALT PERFORMANCE WHILE LOOKING FOR OTHER ACFT WHILE CLBING OUT TO CRUISE ALT. THIS COULD NOT BE CONFIRMED BY S/O. AS TO THE PACK BEING OFF THE CAPT CHKED THEM DURING STABILIZATION STEPS TAKEN. PROBABLE CAUSE WAS OPERATOR ERROR OF UNKNOWN SWITCH POSITIONING IN PRESSURIZATION SYS.

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.