Narrative:

I am a contract maintenance mechanic for several airlines in ZZZ. I have been authority/authorized and trained for each airline to perform gate maintenance repair. On sep/xa/00, I was called to perform an MEL procedure, which called for rudder pressure reducer valve lever to be moved until the word 'high' was visible on the lever and installing locking bolt to secure valve in the high pressure position. This area is a very confined area in and around the horizontal stabilizer inside the aft fuselage. This area is without a doubt the most inaccessible spot I ever encountered. Although the maintenance manual warns of danger in this area, I was very uncomfortable and uneasy. This may have contributed to my judgement. I misinterped which bolt was the proper one. In doing so, I removed the wrong bolt, even though I had the proper instructions with me at the time. The only light I had was a small flashlight. This area could use a ship work area light in this zone. I was also using a mirror while reading information stamped on valve. This was the first time I performed this particular procedure. The aircraft left the gate and landed safely. After reviewing the information I had used in the procedure, I realized the error. I called maintenance operations and informed them. They were to do follow-up maintenance as part of the MEL signoff. Maintenance operations assured me that it was properly repaired and signed off with no damage or adverse effects on flight.

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Original NASA ASRS Text

Title: A B737-300, DURING THE DEFERRAL OF THE YAW DAMPER BY A CONTRACT TECHNICIAN WHO WAS ACCOMPLISHING THE MEL SPECIAL PROC ON THE RUDDER PRESSURE REDUCER VALVE, INADVERTENTLY REMOVED THE WRONG BOLT.

Narrative: I AM A CONTRACT MAINT MECH FOR SEVERAL AIRLINES IN ZZZ. I HAVE BEEN AUTH AND TRAINED FOR EACH AIRLINE TO PERFORM GATE MAINT REPAIR. ON SEP/XA/00, I WAS CALLED TO PERFORM AN MEL PROC, WHICH CALLED FOR RUDDER PRESSURE REDUCER VALVE LEVER TO BE MOVED UNTIL THE WORD 'HIGH' WAS VISIBLE ON THE LEVER AND INSTALLING LOCKING BOLT TO SECURE VALVE IN THE HIGH PRESSURE POS. THIS AREA IS A VERY CONFINED AREA IN AND AROUND THE HORIZ STABILIZER INSIDE THE AFT FUSELAGE. THIS AREA IS WITHOUT A DOUBT THE MOST INACCESSIBLE SPOT I EVER ENCOUNTERED. ALTHOUGH THE MAINT MANUAL WARNS OF DANGER IN THIS AREA, I WAS VERY UNCOMFORTABLE AND UNEASY. THIS MAY HAVE CONTRIBUTED TO MY JUDGEMENT. I MISINTERPED WHICH BOLT WAS THE PROPER ONE. IN DOING SO, I REMOVED THE WRONG BOLT, EVEN THOUGH I HAD THE PROPER INSTRUCTIONS WITH ME AT THE TIME. THE ONLY LIGHT I HAD WAS A SMALL FLASHLIGHT. THIS AREA COULD USE A SHIP WORK AREA LIGHT IN THIS ZONE. I WAS ALSO USING A MIRROR WHILE READING INFO STAMPED ON VALVE. THIS WAS THE FIRST TIME I PERFORMED THIS PARTICULAR PROC. THE ACFT LEFT THE GATE AND LANDED SAFELY. AFTER REVIEWING THE INFO I HAD USED IN THE PROC, I REALIZED THE ERROR. I CALLED MAINT OPS AND INFORMED THEM. THEY WERE TO DO FOLLOW-UP MAINT AS PART OF THE MEL SIGNOFF. MAINT OPS ASSURED ME THAT IT WAS PROPERLY REPAIRED AND SIGNED OFF WITH NO DAMAGE OR ADVERSE EFFECTS ON FLT.

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.