AN INSPECTION PANEL FELL OFF THE HORIZ STABILIZER OF AN ACR MLG. AIRLINE MAINT PROC DEFICIENCY.

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ACFT HAD MISSING HORIZ STABILIZER PANEL L SIDE. AFTER APPROX 4 FLT LEGS; PANEL 9111 WAS FOUND MISSING AT DCA SEP/TUE/94. BEING MY SECOND DAY ON THE MAINT CHK CREW IN TAMPA AFTER 5 YRS WORKING LINE AVIONICS AND MOST RECENT YR AND A HALF WORKING DAYLIGHT (0700-1500); I WAS GIVEN A JOB ASSIGNMENT WITHOUT ANY TRAINING OR FAMILIARIZATION WITH THE ACFT OR MAINT CHK PROCS. THE ASSIGNMENT WAS TO REMOVE 5 HORIZ STABILIZER PANELS L SIDE. HAVE INSPECTION DEPT LOOK FOR MAINT PROBS AND; IF OK; REINSTALL PANELS. MORE TIME WAS NEEDED DURING REMOVAL THAN EXPECTED BECAUSE MANY SCREWS HAD TO BE REMOVED BY DRILLING WHICH IS A TIME CONSUMING TASK. INSTALLATION OF PANELS WAS STARTED ON THE MOST INBOARD SECTION WORKING MY WAY OUT TO PANEL 9111 WHICH IS THE MOST OUTBOARD PANEL REMOVED. MANY SCREWS WERE REMOVED BY DRILLING; WHICH DESTROYS THE SCREWS. BY THE TIME PANEL 9111 WAS REACHED; MANY SCREWS WOULD BE NEEDED. IT MIGHT BE POSSIBLE PANEL 9111 WAS INSTALLED BY ONLY A FEW SCREWS. IN GOING TO GET NEW SCREWS; IT MIGHT BE POSSIBLE I WAS INTERRUPTED AND THE PRESSURE OF BEING BEHIND SCHEDULE; THINGS GOT TURNED AROUND. DOUBLE-CHKING WORK BEFORE SIGNING MAINT CHK CARD SHOWED ALL PANELS WERE INSTALLED. BUT IT MIGHT BE POSSIBLE PANEL 9111 DID NOT HAVE ALL THE SCREWS INSTALLED OR MIGHT BE WRONG SIZE SCREWS. SUPPLEMENTAL INFO FROM ACN 283938: AN INSPECTION PLATE FROM THE UNDERSIDE OF THE HORIZ STABILIZER WAS DISCOVERED MISSING IN DCA. SUPPLEMENTAL INFO FROM ACN 283939: I WAS THE CAPT ON FLT BOS TO DCA; A BOEING 737- 400. IT IS UNSURE AS TO THE EXACT TIME OF DAY OR LOCATION WHICH THE PANEL WAS LOST. I DID THE NECESSARY PREFLT AND ACCEPTANCE ACTIVITIES TO INCLUDE A WALK-AROUND EXTERIOR INSPECTION. NO PANELS WERE MISSING. A WALKAROUND IN BOS WAS NOT REQUIRED BY OUR MANUALS.