Narrative:

Flew a through flight but upon arrival out aircraft was taken for another flight. [We] had to wait 1:30 for another aircraft to continue to our overnight airport. Plane arrived at the gate and was promptly loaded with passengers. When first officer advised that the manual dc outflow valve was inoperative maintenance was called. Upon arrival he confirmed no man dc operation and was prepared to MEL it. I discussed with him that the man aircraft or dc operation could not be MEL'ed (no go item with passengers). I discussed about changing the control module and he agree but thought it would not solve the problem (more like the actuator itself). As the same time this was happening I contacted the ramp tower to find me another aircraft which was done within the hour. We took off near midnight in arriving at our destination 3 hours late. The jest of this report is that had the first officer not forgotten his old checklist and/or flows; we would have never known that the man dc actuator was inoperative. I am not aware of when this item gets check or by whom; I do know that it is no longer in any of our flows (captain or first officer) to test the man AC dc valves. As far as I know this aircraft could have been flying around for days or even months; and from the mechanics comments this was not an isolated case. Again I am not aware of who or when these valves are checked but I think the flow might be revisited to include these no go items.

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Original NASA ASRS Text

Title: A B737-400 First Officer discovered the Manual DC Outflow Valve failed during preflight using an old preflight method which tested the pressurization panel; a procedure not required by new procedures.

Narrative: Flew a through flight but upon arrival out aircraft was taken for another flight. [We] had to wait 1:30 for another aircraft to continue to our overnight airport. Plane arrived at the gate and was promptly loaded with passengers. When First Officer advised that the Manual DC Outflow Valve was inoperative Maintenance was called. Upon arrival he confirmed no MAN DC operation and was prepared to MEL it. I discussed with him that the MAN aircraft or DC operation could not be MEL'ed (no go item with passengers). I discussed about changing the Control Module and he agree but thought it would not solve the problem (more like the actuator itself). As the same time this was happening I contacted the Ramp Tower to find me another aircraft which was done within the hour. We took off near midnight in arriving at our destination 3 hours late. The jest of this report is that had the First Officer not forgotten his old checklist and/or flows; we would have never known that the MAN DC Actuator was inoperative. I am not aware of when this item gets check or by whom; I do know that it is no longer in any of our flows (Captain or First Officer) to test the MAN AC DC valves. As far as I know this aircraft could have been flying around for days or even months; and from the Mechanics comments this was not an isolated case. Again I am not aware of who or when these valves are checked but I think the flow might be revisited to include these no go items.

Data retrieved from NASA's ASRS site as of April 2012 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.