A B747-400 WAS DISPATCHED WITH THE L FMS INOP DUE TO AN AUTOPLT FLT CTL COMPUTER BEING INADVERTENTLY INSTALLED IN THE FMC POS.

Narrative

ON JAN/FRI/05 I WAS ASSISTING ANOTHER TECHNICIAN WHO WAS CALLED OUT FOR A PROB ON A B747-400. THE DISCREPANCY WAS: 'R FMC DATA OUT OF TIME.' WHILE IN THE COCKPIT LOOKING AT THIS PROB; THE L FMC 'LOCKED UP' AND WAS EFFECTIVELY INOP. SINCE THIS MEANT THAT THERE WERE 2 FMC'S NOW INOP; 1 OF THEM HAD TO BE FIXED; SINCE THE MEL WILL ONLY ALLOW 1 FMC TO BE INOP. WE ATTEMPTED TO ORDER THE L FMC FROM STOCK AND WERE INFORMED THAT THERE WERE NONE IN STOCK. WE NOW HAD TO 'ROB' THE PART FROM ANOTHER ACFT SINCE THE ONE WE WERE WORKING ON WAS SCHEDULED TO DEPART FOR ZZZZ. WHILE REMOVING OR ROBBING THE PART FROM ANOTHER ACFT; I INADVERTENTLY REMOVED A FLT CTL COMPUTER INSTEAD OF A FLT MGMNT COMPUTER AND INSTALLED IT ON THE ACFT WE WERE WORKING ON. WE THEN WENT TO LOAD THE DATABASE ON THE FMC THAT WE THOUGHT WE HAD INSTALLED; BUT REALLY DIDN'T BECAUSE I HAD CHANGED THE WRONG COMPUTER. HOWEVER; WE WERE; AFTER A TIME; ABLE TO LOAD THE DATABASE AND THE L FMC STARTED FUNCTIONING NORMALLY AND TESTED NORMALLY PER THE MAINT MANUAL. WE THEN DEFERRED THE R FMC PER THE APPLICABLE MEL. WHILE WE WERE COMPLETING THE LOGBOOK ENTRIES; WE REALIZED THAT THE WRONG PART HAD BEEN CHANGED; SO WE ATTEMPTED TO SET UP MORE TIME TO CORRECT THE SIT WHEN MGMNT (LINE MAINT MGR ON DUTY AT THE TIME); OVERRODE OUR DECISION AND CALLED THE ACFT GOOD TO GO AND THE ACFT DEPARTED FOR ZZZZ. I THEN GENERATED A NON ROUTINE WORK CARD FOR THE FCC THAT I CHANGED AND DEFERRED IT INCORRECTLY TO VISUAL CHK INSTEAD OF AN AUTOLAND CONFIGN DEFERRAL THAT IT SHOULD HAVE HAD; SO THE ACFT DEPARTED WITHOUT THE PROPER AUTOLAND CONFIGN CHKOUT THAT IT SHOULD HAVE HAD. TO MY KNOWLEDGE; NO MESSAGES WERE GENERATED INFLT AND THE SYS OPERATED NORMALLY. I DON'T BELIEVE THAT THERE WAS ANY SAFETY OF FLT ISSUE SINCE THE L FMC WAS OPERATING NORMALLY AND BOTH L AND R FCC'S WERE OPERATING NORMALLY. UPON ARR IN ZZZZ; THE L FCC WAS REPLACED AND AUTOLAND CONFIGN QUALIFIED; AND UPON ARR BACK IN ZZZ; THE R FMC WAS REPLACED PER THE APPLICABLE MAINT MANUALS.