MECH OF ACR LGT ACFT INADVERTENTLY LEFT 1 OF THE 3 ENGS IN A TEST POS RESULTING IN THE ACFT OPERATING WITH LESS THAN THE MAX AVAILABLE PWR.

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I WAS ASSIGNED WITH ANOTHER MECH TO PERFORM A #2 ENG TRIM ON LGT. THE MECH WHICH WAS WORKING WITH ME HAD NEVER PERFORMED AN ENG TRIM ON A LGT TYPE ACFT. HE WAS ASSIGNED TO WORK WITH ME AS I SHOWED HIM HOW TO DO ONE. THE TRIM EQUIP WAS BROUGHT TO THE PLANE AND WAS ATTACHED TO THE ACFT AS SPECIFIED BY THE MAINT MANUAL. AT THIS POINT; APPROX AM00 HRS; THE PARTIAL PWR STOP ON THE #2 ENG'S FUEL CTL UNIT WAS SAFETY WIRED IN THE PARTIAL PWR POS. THE LGT WAS NOW READY TO GO TO THE RUNUP BLOCKS FOR THE ENG TRIM. AT THIS POINT; THE TRIM BOX WAS CHKED BY MYSELF AND FOUND TO BE INOP. I INFORMED MY SUPVR AND HE INFORMED MAINT CTL. THEY TOLD US TO STANDBY WHILE THEY TRIED TO GET A DEFERRAL FOR THE D.I.P. ON ACFT. AS I WAS WAITING FOR INSTRUCTIONS A WDB ACFT ON ITS WAY TO PARIS MADE AN AIR RETURN FOR A CRACKED L3 WINDOW. I WAS ASKED TO PERFORM AN L3 WINDOW CHANGE. AT THIS TIME I GAVE A VERBAL TURNOVER TO THE MECH WHICH I WAS WORKING WITH. I TOLD HIM WHEN THE ENG TRIM GETS DEFERRED; DISCONNECT THE ENG TRIM EQUIP AND PUT THE PARTIAL PWR STOP BACK TO ITS ORIGINAL POS. HE AGREED TO THIS. I COMPLETED THE L3 WINDOW CHANGE ON THE WDB ACFT AND PROCEEDED BACK TO MY WORK PLACE. I ASKED MY SUPVR IF THE ENG TRIM HAD BEEN DEFERRED; AND HE SAID YES. I WENT OUT TO ACFT AND THE OTHER MECH APCHED ME AND TOLD ME THE EQUIP WAS DISCONNECTED AND THE PLANE WAS READY FOR ITS DEP. THE PLANE DEPARTED WITH THE PARTIAL PWR STOP IN PARTIAL PWR POS. THE CREW OF MLG ACFT WAS ENRTE TO CLE; OH. ON DEP; THEY LOGGED THAT THEY DID NOT REACH MAX CLB PWR FROM #2 ENG AND IT FELT AS IF IT WAS HAVING A THROTTLE BINDING. IT LANDED IN OH; AND MAINT FOUND THE #2 ENGS FUEL CTL UNIT TO HAVE THE PARTIAL PWR STOP IN THE PARTIAL PWR POS. THEY SET THE STOP BACK AND CORRECTED THE PROBLEM. I FEEL THE PROBLEM COULD HAVE BEEN AVOIDED IF I WOULD HAVE MADE A MAINT ENTRY IN THE LOGBOOK OR IF I WOULD HAVE CHKED THE MECH'S WORK AFTER I ASKED IF THE EQUIP AND PLANE WERE RESTORED TO NORMAL. ANOTHER FACTOR IN THIS SITUATION WAS THE DELAY ON THE DEFERRAL BY MAINT CTL. A BIG FACTOR IN MY OPINION WAS THE URGENCY OF THE WDB ACFT THAT MADE THE AIR RETURN. THE SUPVRS OF MAINT WERE IN A HURRY TO GET THE WDB ACFT BACK OFF THE DEP GATE SO THE FLT WOULD NOT BE CANCELLED BECAUSE THE CREW WOULD HAVE BEEN ILLEGAL. THE DECISION TO LET MY WORK BE IN THE HANDS OF ANOTHER MECH WAS WRONG. I SHOULD HAVE CHKED THE WORK MYSELF. I SHOULD HAVE FINISHED 1 JOB BEFORE THE NEXT; BUT MY SUPVR PUT ME ON THE WDB ACFT TO WORK. NOW I UNDERSTAND THE IMPORTANCE OF MAKING OPEN LOG WRITE-UPS FOR UNFINISHED WORK. NEXT TIME THE DECISIONS WILL BE THE RIGHT ONES. I WILL NOT RELY ON ANYONE TO COMPLETE MY WORK. SUPPLEMENTAL INFO FROM ACN 208492: SCHEDULED PAX FLT EWR TO CLE. MADE 'REDUCED PWR' TKOF IN EWR. ALL ENGS NORMAL; APPROX 90% N1. HAD TO LEVEL OFF APPROX 8000 FT DUE TO TFC. AFTER SETTING CLB PWR; ENGINEER SAID #2 THROTTLE FELT FUNNY. HE SAID THE THROTTLE WOULDN'T GO FORWARD PAST SOME POINT. WE HAD VERY SLIGHTLY LESS THAN CLB PWR ON #2. I TRIED PUSHING THE #2 THROTTLE UP. I COULD MOVE IT ABOUT AN INCH FURTHER BUT THE RPM DIDN'T CHANGE AND THE THROTTLE CAME BACK TO THE SAME POINT. NOTIFIED MAINT IN CLE AND WROTE UP THE #2 THROTTLE ON ARR. DAYS LATER; FOUND OUT THAT MAINT HAD WORKED ON THE ACFT PRIOR TO MY FLT. THEY HAD INSTALLED A 'PARTIAL PWR STOP PIN' ON #2 THROTTLE. THIS SUPPOSEDLY LIMITS THE THROTTLE MOVEMENT PAST APPROX 70 OR 80% N1. I HAVE FLOWN ALL 3 POS ON THE LGT OVER THE LAST 20 YRS. THIS IS THE FIRST TIME I EVER HEARD OF A 'PARTIAL PWR STOP PIN.' IT IS STRICTLY A MAINT FUNCTION. SOME BOOBY TRAP!