Narrative:

On oct/sat/03, I was to work an airbus A320. 5 mins before departure I was called to the flight deck for an avionics system vent fault. I performed the bite test and found the skin extract valve to be at fault. I proceeded to defer the valve per MEL 21-26-04. While performing the requirements of the MEL, I mistakenly locked open the main flap of the extract valve instead of the internal flap of the main flap. As a result the aircraft gained altitude but could not pressurize resulting in a landing and return to gate. Human factors involved: besides the maintenance action on the valve I also needed to do a departure walkaround and assist with air and air start (inoperative APU). I wasn't being rushed but was a little overwhelmed. I was not familiar with the MEL procedure. The opening of the internal flap is explained clearly on a note on page 3 of the MEL right before section B. I overlooked this important note because section B is the procedure for the opening of the skin exchange isolation valve which is also part of the MEL. Feeling that I had completed the procedure for the main flap I prematurely moved on to the isolation valve.

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Original NASA ASRS Text

Title: AN AIRBUS 320 WAS DISPATCHED IN NON COMPLIANCE WITH THE SKIN AIR EXTRACT VALVE DEFERRED PER THE MEL BUT VALVE POSITIONED INCORRECTLY. ACFT RETURNED UNABLE TO PRESSURIZE.

Narrative: ON OCT/SAT/03, I WAS TO WORK AN AIRBUS A320. 5 MINS BEFORE DEP I WAS CALLED TO THE FLT DECK FOR AN AVIONICS SYS VENT FAULT. I PERFORMED THE BITE TEST AND FOUND THE SKIN EXTRACT VALVE TO BE AT FAULT. I PROCEEDED TO DEFER THE VALVE PER MEL 21-26-04. WHILE PERFORMING THE REQUIREMENTS OF THE MEL, I MISTAKENLY LOCKED OPEN THE MAIN FLAP OF THE EXTRACT VALVE INSTEAD OF THE INTERNAL FLAP OF THE MAIN FLAP. AS A RESULT THE ACFT GAINED ALT BUT COULD NOT PRESSURIZE RESULTING IN A LNDG AND RETURN TO GATE. HUMAN FACTORS INVOLVED: BESIDES THE MAINT ACTION ON THE VALVE I ALSO NEEDED TO DO A DEP WALKAROUND AND ASSIST WITH AIR AND AIR START (INOP APU). I WASN'T BEING RUSHED BUT WAS A LITTLE OVERWHELMED. I WAS NOT FAMILIAR WITH THE MEL PROC. THE OPENING OF THE INTERNAL FLAP IS EXPLAINED CLRLY ON A NOTE ON PAGE 3 OF THE MEL RIGHT BEFORE SECTION B. I OVERLOOKED THIS IMPORTANT NOTE BECAUSE SECTION B IS THE PROC FOR THE OPENING OF THE SKIN EXCHANGE ISOLATION VALVE WHICH IS ALSO PART OF THE MEL. FEELING THAT I HAD COMPLETED THE PROC FOR THE MAIN FLAP I PREMATURELY MOVED ON TO THE ISOLATION VALVE.

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.