Narrative:

This started with a gate return for #1 engine cowl anti-ice valve discrepancy. Mr X and I found out that MEL was the only option; because we had no valve in stock. Rain was coming down and we wanted to get the passenger on their way safely in a timely manner. We read the MEL and proceeded to work maintenance procedures. Had 2 parts. I took the first; that was to lock out the cowl valve. Mr X took the second; which was to lock the high stage valve. Mr X had notified me that the bolt to lock the high stage valve had sheared; which is not uncommon. My focus diverted; because I knew high stage valve replacement was not easy. Per maintenance procedures I had to stow the tai pressure switch canon plug. In error I stowed the anti-ice valve canon plug. Both plugs are in the same area. I feel the MEL paperwork for this maintenance procedure is too generic; but I take full responsibility for my error. In the future I will take a step back and carefully understand my paperwork so the aircraft will go out safely and properly. Callback conversation with reporter revealed the following information: reporter stated that part of the MEL procedure mechanics use; includes a diagram to disconnect the tai pressure switch canon plug on the nose cowl anti-ice valve; wrap it in a plastic bag and stow the connector. However; there are two canon plugs on this same anti-ice valve in close proximity to each other. The MEL procedure diagram only shows one canon plug wrapped and stowed on this valve; without any reference to there being two different connectors. Reporter also stated he has done this procedure before. Yet somehow; he didn't catch the wording that referenced the pressure switch (tai) on the diagram. Instead; he disconnected the shut-off valve's connector. Reporter stated he has requested to his carrier that a revision be made to the MEL deferral procedure to include both canon plug connectors. The MM diagram does specifically show the different canon plug connectors.

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Original NASA ASRS Text

Title: A B737-700 RETURNED TO GATE DUE TO ANTI-ICE VALVE DISCREPANCY. MECHANIC PERFORMING MEL PROCEDURE MISTAKENLY DISCONNECTED AND STOWED THE ANTI-ICE VALVE CANON PLUG INSTEAD OF THE REQUIRED TAI PRESSURE SWITCH CANON PLUG.

Narrative: THIS STARTED WITH A GATE RETURN FOR #1 ENG COWL ANTI-ICE VALVE DISCREPANCY. MR X AND I FOUND OUT THAT MEL WAS THE ONLY OPTION; BECAUSE WE HAD NO VALVE IN STOCK. RAIN WAS COMING DOWN AND WE WANTED TO GET THE PAX ON THEIR WAY SAFELY IN A TIMELY MANNER. WE READ THE MEL AND PROCEEDED TO WORK MAINT PROCS. HAD 2 PARTS. I TOOK THE FIRST; THAT WAS TO LOCK OUT THE COWL VALVE. MR X TOOK THE SECOND; WHICH WAS TO LOCK THE HIGH STAGE VALVE. MR X HAD NOTIFIED ME THAT THE BOLT TO LOCK THE HIGH STAGE VALVE HAD SHEARED; WHICH IS NOT UNCOMMON. MY FOCUS DIVERTED; BECAUSE I KNEW HIGH STAGE VALVE REPLACEMENT WAS NOT EASY. PER MAINT PROCS I HAD TO STOW THE TAI PRESSURE SWITCH CANON PLUG. IN ERROR I STOWED THE ANTI-ICE VALVE CANON PLUG. BOTH PLUGS ARE IN THE SAME AREA. I FEEL THE MEL PAPERWORK FOR THIS MAINT PROC IS TOO GENERIC; BUT I TAKE FULL RESPONSIBILITY FOR MY ERROR. IN THE FUTURE I WILL TAKE A STEP BACK AND CAREFULLY UNDERSTAND MY PAPERWORK SO THE ACFT WILL GO OUT SAFELY AND PROPERLY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THAT PART OF THE MEL PROCEDURE MECHANICS USE; INCLUDES A DIAGRAM TO DISCONNECT THE TAI PRESSURE SWITCH CANON PLUG ON THE NOSE COWL ANTI-ICE VALVE; WRAP IT IN A PLASTIC BAG AND STOW THE CONNECTOR. HOWEVER; THERE ARE TWO CANON PLUGS ON THIS SAME ANTI-ICE VALVE IN CLOSE PROXIMITY TO EACH OTHER. THE MEL PROCEDURE DIAGRAM ONLY SHOWS ONE CANON PLUG WRAPPED AND STOWED ON THIS VALVE; WITHOUT ANY REFERENCE TO THERE BEING TWO DIFFERENT CONNECTORS. REPORTER ALSO STATED HE HAS DONE THIS PROCEDURE BEFORE. YET SOMEHOW; HE DIDN'T CATCH THE WORDING THAT REFERENCED THE PRESSURE SWITCH (TAI) ON THE DIAGRAM. INSTEAD; HE DISCONNECTED THE SHUT-OFF VALVE'S CONNECTOR. REPORTER STATED HE HAS REQUESTED TO HIS CARRIER THAT A REVISION BE MADE TO THE MEL DEFERRAL PROCEDURE TO INCLUDE BOTH CANON PLUG CONNECTORS. THE MM DIAGRAM DOES SPECIFICALLY SHOW THE DIFFERENT CANON PLUG CONNECTORS.

Data retrieved from NASA's ASRS site as of January 2009 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.