Narrative:

During climb out to a cruise altitude of FL330 from mkc to pit we detected the audible cabin pressure warning horn and noted a cabin pressure altitude of approximately 9500 ft (and climbing). To preclude any further deterioration of the situation that might have resulted in the need for a full emergency descent and deployment of the passenger oxygen system, the captain elected to descend to a lower altitude. Upon promptly receiving clearance from ARTCC we began an initial descent to FL250 during which we conducted the rapid depressurization immediate action procedures. We both initially assessed the problem as a malfunction of the automatic portion of our pressurization controller as the captain was able to restore pressurization in the standby mode. During his corrective actions however, the captain found the 'land altitude' window set with a 10000 ft error based on my transposing pit's 1203 ft field elevation into the same digits placed in the 'land altitude' window 1 decimal point to the left. During preflight I had set the cabin pressurization control panel for cruise flight in our medium large transport Y to FL330 in the 'flight altitude' window, 1003 MSL in the 'cabin attendant altitude' window (200 ft below landing field elevation in accordance with the flight manual), and 1203 MSL in the land altitude window or so I thought. Just prior to the gate agent's load confirmation, the captain and I accomplished the before start checklist. After pushback and engine start we taxied for an uneventful takeoff and initial climb. During our descent to FL250, the captain discovered that I had in fact entered 12030 MSL in the 'land altitude' window instead of 1203 MSL which we both had 'seen' during our preflight checklist accomplishment. In effect, the automatic pressure controller was performing as it was instructed by climbing the cabin to 12030 MSL. After reaching a lower altitude with the pressurization stabilized, the captain visited the passenger cabin to explain the reason for our unplanned descent. Several passenger were reassured as to safety of the flight and we proceeded to an on-time arrival at pit. Having, unfortunately, one of the best seats in the house for observing my own mistake and its immediate consequences, I've had the opportunity to be reminded how one shouldn't stay in a profession unless he thinks he can learn something new every time he goes out and (in my case) flies. While there is no excuse for me to have not seen what really had been set in the pressure controller, I'm afraid my 61 hours of time in the aircraft since initial training perhaps had a role in limiting the depth of detail I had developed over the past 3 yrs while flying the medium large transport X model. Supplemental information from acn 206157: during this time, I did not declare an emergency or take priority over any other aircraft while changing altitude. Our checklist calls for the captain to check the pressurization settings before takeoff. These settings are put in by the first officer since the cabin altitude controller is above the first officer. When pressurization check was called for on the checklist, I did look over and say 12?, but did not count the zeros. The first officer put in 12000 ft and I read it as 1200 ft. Next time, I'll slow down and read what it says and not what I wanted it to say.

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Original NASA ASRS Text

Title: AMENDED CLRNC REQUESTED BY FLC AFTER TEMPORARY LOSS OF CTL OF CABIN PRESSURE.

Narrative: DURING CLBOUT TO A CRUISE ALT OF FL330 FROM MKC TO PIT WE DETECTED THE AUDIBLE CABIN PRESSURE WARNING HORN AND NOTED A CABIN PRESSURE ALT OF APPROX 9500 FT (AND CLBING). TO PRECLUDE ANY FURTHER DETERIORATION OF THE SITUATION THAT MIGHT HAVE RESULTED IN THE NEED FOR A FULL EMER DSCNT AND DEPLOYMENT OF THE PAX OXYGEN SYS, THE CAPT ELECTED TO DSND TO A LOWER ALT. UPON PROMPTLY RECEIVING CLRNC FROM ARTCC WE BEGAN AN INITIAL DSCNT TO FL250 DURING WHICH WE CONDUCTED THE RAPID DEPRESSURIZATION IMMEDIATE ACTION PROCS. WE BOTH INITIALLY ASSESSED THE PROBLEM AS A MALFUNCTION OF THE AUTOMATIC PORTION OF OUR PRESSURIZATION CTLR AS THE CAPT WAS ABLE TO RESTORE PRESSURIZATION IN THE STANDBY MODE. DURING HIS CORRECTIVE ACTIONS HOWEVER, THE CAPT FOUND THE 'LAND ALT' WINDOW SET WITH A 10000 FT ERROR BASED ON MY TRANSPOSING PIT'S 1203 FT FIELD ELEVATION INTO THE SAME DIGITS PLACED IN THE 'LAND ALT' WINDOW 1 DECIMAL POINT TO THE L. DURING PREFLT I HAD SET THE CABIN PRESSURIZATION CTL PANEL FOR CRUISE FLT IN OUR MLG Y TO FL330 IN THE 'FLT ALT' WINDOW, 1003 MSL IN THE 'CAB ALT' WINDOW (200 FT BELOW LNDG FIELD ELEVATION IN ACCORDANCE WITH THE FLT MANUAL), AND 1203 MSL IN THE LAND ALT WINDOW OR SO I THOUGHT. JUST PRIOR TO THE GATE AGENT'S LOAD CONFIRMATION, THE CAPT AND I ACCOMPLISHED THE BEFORE START CHKLIST. AFTER PUSHBACK AND ENG START WE TAXIED FOR AN UNEVENTFUL TKOF AND INITIAL CLB. DURING OUR DSCNT TO FL250, THE CAPT DISCOVERED THAT I HAD IN FACT ENTERED 12030 MSL IN THE 'LAND ALT' WINDOW INSTEAD OF 1203 MSL WHICH WE BOTH HAD 'SEEN' DURING OUR PREFLT CHKLIST ACCOMPLISHMENT. IN EFFECT, THE AUTOMATIC PRESSURE CTLR WAS PERFORMING AS IT WAS INSTRUCTED BY CLBING THE CABIN TO 12030 MSL. AFTER REACHING A LOWER ALT WITH THE PRESSURIZATION STABILIZED, THE CAPT VISITED THE PAX CABIN TO EXPLAIN THE REASON FOR OUR UNPLANNED DSCNT. SEVERAL PAX WERE REASSURED AS TO SAFETY OF THE FLT AND WE PROCEEDED TO AN ON-TIME ARR AT PIT. HAVING, UNFORTUNATELY, ONE OF THE BEST SEATS IN THE HOUSE FOR OBSERVING MY OWN MISTAKE AND ITS IMMEDIATE CONSEQUENCES, I'VE HAD THE OPPORTUNITY TO BE REMINDED HOW ONE SHOULDN'T STAY IN A PROFESSION UNLESS HE THINKS HE CAN LEARN SOMETHING NEW EVERY TIME HE GOES OUT AND (IN MY CASE) FLIES. WHILE THERE IS NO EXCUSE FOR ME TO HAVE NOT SEEN WHAT REALLY HAD BEEN SET IN THE PRESSURE CTLR, I'M AFRAID MY 61 HRS OF TIME IN THE ACFT SINCE INITIAL TRAINING PERHAPS HAD A ROLE IN LIMITING THE DEPTH OF DETAIL I HAD DEVELOPED OVER THE PAST 3 YRS WHILE FLYING THE MLG X MODEL. SUPPLEMENTAL INFO FROM ACN 206157: DURING THIS TIME, I DID NOT DECLARE AN EMER OR TAKE PRIORITY OVER ANY OTHER ACFT WHILE CHANGING ALT. OUR CHKLIST CALLS FOR THE CAPT TO CHK THE PRESSURIZATION SETTINGS BEFORE TKOF. THESE SETTINGS ARE PUT IN BY THE FO SINCE THE CABIN ALT CTLR IS ABOVE THE FO. WHEN PRESSURIZATION CHK WAS CALLED FOR ON THE CHKLIST, I DID LOOK OVER AND SAY 12?, BUT DID NOT COUNT THE ZEROS. THE FO PUT IN 12000 FT AND I READ IT AS 1200 FT. NEXT TIME, I'LL SLOW DOWN AND READ WHAT IT SAYS AND NOT WHAT I WANTED IT TO SAY.

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.