Narrative:

Aircraft was dispatched with automatic pressure control inoperative -- requiring use of manual pressure control -- a very unusual situation (third or fourth time in my 14 yrs as captain on aircraft). During climb out through approximately 17000 ft cabin altitude horn sounded indicating cabin altitude 10000 ft. Depressurization procedures were followed, cargo heat outflow closed and manual pressure control clockwise to stop cabin climb. Cabin continued climbing as descent was coordinated with center and initiated. Passenger oxygen masks deployed as cabin altitude went through 14000 ft before aircraft could be descended through that altitude. Aircraft continued descent to 8000 ft. Fuel was dumped to maximum landing weight as aircraft returned to ord. Approach and landing were uneventful. Contributing factors were 1) the operating manual procedure with respect to operating in 'manual mode only' were basically non-existent, 2) very new flight engineer on panel with minimal training with respect to manual pressure operation. 3) a 'freak' coincidence in that the cabin altitude needle was superimposed directly below the cabin pressure differential needle on the 'outer dial/inner dial' dual reading gauge at the instant the horn went off -- momentarily delaying verification of actual cabin altitude and subsequent crew reactions. Supplemental information from acn 215778: since turning manual cabin pressure control knob full clockwise did not arrest cabin control, this leads me to believe that outflow valve was stuck in open position. In addition, operating manual does not provide instructions on operational use of manual cabin control nor is any training given on use of manual cabin pressure control operations.

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Original NASA ASRS Text

Title: ACR LGT MAKES A RAPID DSCNT AFTER LOSING CABIN PRESSURE AND AUTOMATIC DEPLOYMENT OF OXYGEN MASKS IS EXPERIENCED.

Narrative: ACFT WAS DISPATCHED WITH AUTOMATIC PRESSURE CTL INOP -- REQUIRING USE OF MANUAL PRESSURE CTL -- A VERY UNUSUAL SITUATION (THIRD OR FOURTH TIME IN MY 14 YRS AS CAPT ON ACFT). DURING CLBOUT THROUGH APPROX 17000 FT CABIN ALT HORN SOUNDED INDICATING CABIN ALT 10000 FT. DEPRESSURIZATION PROCS WERE FOLLOWED, CARGO HEAT OUTFLOW CLOSED AND MANUAL PRESSURE CTL CLOCKWISE TO STOP CABIN CLB. CABIN CONTINUED CLBING AS DSCNT WAS COORDINATED WITH CTR AND INITIATED. PAX OXYGEN MASKS DEPLOYED AS CABIN ALT WENT THROUGH 14000 FT BEFORE ACFT COULD BE DSNDED THROUGH THAT ALT. ACFT CONTINUED DSCNT TO 8000 FT. FUEL WAS DUMPED TO MAX LNDG WT AS ACFT RETURNED TO ORD. APCH AND LNDG WERE UNEVENTFUL. CONTRIBUTING FACTORS WERE 1) THE OPERATING MANUAL PROC WITH RESPECT TO OPERATING IN 'MANUAL MODE ONLY' WERE BASICALLY NON-EXISTENT, 2) VERY NEW FE ON PANEL WITH MINIMAL TRAINING WITH RESPECT TO MANUAL PRESSURE OPERATION. 3) A 'FREAK' COINCIDENCE IN THAT THE CABIN ALT NEEDLE WAS SUPERIMPOSED DIRECTLY BELOW THE CABIN PRESSURE DIFFERENTIAL NEEDLE ON THE 'OUTER DIAL/INNER DIAL' DUAL READING GAUGE AT THE INSTANT THE HORN WENT OFF -- MOMENTARILY DELAYING VERIFICATION OF ACTUAL CABIN ALT AND SUBSEQUENT CREW REACTIONS. SUPPLEMENTAL INFO FROM ACN 215778: SINCE TURNING MANUAL CABIN PRESSURE CTL KNOB FULL CLOCKWISE DID NOT ARREST CABIN CTL, THIS LEADS ME TO BELIEVE THAT OUTFLOW VALVE WAS STUCK IN OPEN POS. IN ADDITION, OPERATING MANUAL DOES NOT PROVIDE INSTRUCTIONS ON OPERATIONAL USE OF MANUAL CABIN CTL NOR IS ANY TRAINING GIVEN ON USE OF MANUAL CABIN PRESSURE CTL OPS.

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.