A B737-700 WAS DISPATCHED IN NON COMPLIANCE WITH INTERMIXED THRUST RATED ENGS. THE ENG IDENT AND CONFIGN WAS CONFIRMED USING THE FMS DISPLAY. MUST USE ENG DATA PLATE.

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ON JUN/MON/04; ACFT #1 ENG CHANGE. I FOLLOWED THE PAPERWORK ISSUE; ALONG WITH MAINT MANUAL REF CALLED OUT. THE ACFT WAS LATER DISCOVERED TO HAVE INTERMIXED ENGS. AS PER MT771-00-01 STEP 1B; 'WARNING; BOTH ENGS ON THE SAME ACFT MUST BE AT THE SAME THRUST RATING.' I CONFIRMED THIS WHEN I PERFORMED STEP 170; USING THE MAINT MANUAL TEST 9 (71-00-00-5); STEP D4C; THE SCREEN ON THE FMC THAT GIVES YOU IDENT/CONFIGN. READ BOTH ENGS WERE AT '24K' IT HAS NOW BEEN BROUGHT TO MY ATTN THAT ACO X; THE PAPERWORK WHICH WAS NOT ISSUED ON JUN/MON/04; DEALS WITH DIP SWITCH SETTING; WHICH CAN MAKE AN FMC DISPLAY '22K' OR '24K;' AND NOT MATCH THE TRUE ENG RATING. THE ONLY WAY TO CONFIRM ENG RATING IS TO READ IT OFF THE ENG DATA PLATE AND SET THE DIP SWITCH TO MATCH. SUPPLEMENTAL INFO FROM ACN 621294: ON JUN/MON/04; WHILE ACFT UNDERWENT AN ENG CHANGE IN THE #1 POS; ENG CHANGE JOB CARD #771-00-01 ALONG WITH THE MAINT MANUAL REFS IT CALLED OUT FOR WERE FOLLOWED. LATER THE ACFT WAS FOUND TO HAVE INTERMIXED ENGS. WHILE WITNESSING THE MECH PERFORMING THE REQUIRED TESTS PER ENGINE CHARGE JOB CARD #771-00-01 REVISION DATE MAY/WED/04 STEP 170; USING TEST 9 OF THE MAINT MANUAL 71-00-00-5; STEP D4C. I CONFIRMED THE IDENT/CONFIGN SCREEN FOR BOTH ENGS RATED AT '24K.' LATER I WAS NOTIFIED THAT THE ACFT LEFT WITH INTERMIXED ENGS DUE TO ACO X AND CCO Y WERE NOT ISSUED; WHICH WOULD HAVE PREVENTED THIS EVENT. AS OF JUN/SAT/04; THE ENGINE CHARGE JOB CARD HAS BEEN REVISED TO ADDRESS READING THE ACTUAL ENG RATING AT THE DATA PLATE; BUT ALSO I FEEL THE MAINT MANUAL SHOULD BE REVISED AS WELL TO REQUIRE THE SAME.