A B757 FLC FAILED TO NOTE THAT THEIR EICAS COMPUTER SWITCH WAS NOT IN THE AUTO POS DURING THEIR USE OF THE 'THROUGH FLT' CHKLIST OUT OF MIA; FL.

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CREW ACCOMPLISHED THROUGH FLT ON ACFT THAT PREVIOUSLY FLEW SAME DAY WITH NO ITEMS ENTERED IN MAINT LOGBOOK. A CHK BY MAINT WAS ALSO COMPLETED AT ZZZ BY MAINT. AFTER AIRBORNE; FO NOTICED EICAS COMPUTER SWITCH IN R COMPUTER INSTEAD OF AUTO POS. UPON REPOSITION TO AUTO POS; LOWER EICAS WAS INOP UNLESS EICAS COMPUTER SWITCH PLACED TO R COMPUTER SELECTION. SENT 'FMR' MESSAGE; CHKED MEL WHICH REFED PLACING STANDBY ENG INSTS SWITCH TO 'ON' POS AND NOTED APPLICABLE CONTINGENCIES IN EVENT OF FUTURE DISPLAY FAILURE. LANDED AT DEST WITHOUT INCIDENT; MAINT RESET COMPUTERS; FAULTS CLRED. RECOMMEND TO AIRCREWS AND MAINT THE IMPORTANCE OF PUTTING SWITCHES BACK INTO NORMAL POS AND OR WRITING UP MALFUNCTIONS SO THAT FUTURE CREWS ON THROUGH FLTS; ETC; DO NOT GET STUCK WITH A PREVIOUSLY EXISTING PROB. THE THROUGH FLT PHILOSOPHY RELIES; TO A LARGE EXTENT; UPON CHKING CERTAIN ITEMS AND RELYING UPON MOST SWITCHES AND SYS HAVING PREVIOUSLY BEEN SET AND CHKED. IF NO ITEMS ENTERED IN LOGBOOK; THEN THE CREWS ASSUME SYS WORKS OK. IT IS DIFFICULT TO DETECT INSIDIOUS MALFUNCTIONS LIKE AN EICAS COMPUTER FAILURE WHEN THE OTHER COMPUTER IS SELECTED AND OPS NORMAL.