A B737-200 WAS RETURNED TO SVC WITH 3 MAIN BIAS PLY TIRES AND 1 RADIAL TIRE INADVERTENTLY INSTALLED IN CONFLICT WITH THE MAINT MANUAL.

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ON 07/SUN/02 AT ABOUT XA00; I WAS DOING MAINT CHKS ON A B737-200 COMBINATION. I NOTED THAT 3 OF THE 4 MAIN GEAR TIRES WERE WORN TO THE SVC LIMIT. I SUBSEQUENTLY REPLACED THE TIRES WITH BIAS PLY TIRES FROM STOCK AT OUR MAIN HANGAR. THE NEXT DAY WHEN THIS ACFT WENT BACK INTO SVC; IT WAS NOTED BY OTHER MAINT PERSONNEL THAT THE ACFT HAD 3 BIAS PLY TIRES; AND 1 RADIAL PLY TIRE ON THE MAIN LNDG GEAR. THIS IS INCORRECT AS THE ACFT MUST HAVE ALL THE SAME TYPE TIRE ON THE LNDG GEAR; MIXING OF RADIAL TIRES AND BIAS PLY TIRES ARE NOT APPROVED. WE HAVE HAD TRAINING ON CHANGING OVER TO THESE RADIAL TIRES; AND NEW TYPE BRAKES. THE NEW RADIAL TIRES AND WHEELS MUST BE USED ON ALL 4 AXLES; WITH THE NEW STYLE BRAKES. ONCE AN ACFT HAS BEEN MODIFIED WITH THE NEW BRAKES AND WHEELS/TIRES; IT CANNOT USE OLD STYLE BRAKES/BIAS TIRES. AS YET; X AIRLINES HAS NOT MODIFIED OUR FLEET OF B737-400; -700; AND -900 ACFT TO THE NEW BRAKES/TIRES. HOWEVER; THE B737-200 ACFT HAVE BEEN MODIFIED TO ACCEPT THE RADIAL TIRES AND NEW BRAKES. THIS KNOWLEDGE HAS NOT BEEN WIDELY KNOWN AMONGST MAINT PERSONNEL. I DID NOT KNOW ALL OF OUR -200 ACFT HAD HAD THIS MODIFICATION. NONE OF X AIRLINES B737-400 ACFT HAVE HAD THIS MODIFICATION. THE CONTRIBUTING FACTORS ARE THAT WE HAD USED THE SAME MAIN GEAR TIRE ASSEMBLY ON BOTH THE B737-200 AND B737-400. ALSO THAT THE IDENT TAGS ON THE TIRES STATE '737-200/400.' AS I PREVIOUSLY STATED; IT HAS NOT BEEN WIDELY KNOWN THAT ALL B737-200 ACFT MUST USE THE NEW TIRES AND BRAKES. FINALLY; THE ZZZ BASE DOES NOT SVC THE B737-200 ON A REGULAR BASIS; BECAUSE THIS ACFT IS USED MOSTLY; SVCED BY THE ZZZ1 BASE MORE OFTEN THAN ZZZ. I WAS INFORMED OF THIS ERROR UPON RETURNING TO WORK. SUBSEQUENTLY; I HAD A CONVERSATION WITH THE LINE MAINT MGR AT ZZZ. HE ASKED FOR MY SUGGESTIONS TO PREVENT THIS ERROR FROM RECURRING. I STATED THAT I WOULD REREAD (RETRAINING) THE MAINT LETTER ABOUT THE MODIFICATION. I ALSO SUGGESTED WE PLACARD THE LNDG GEAR DOORS WITH TIRE AND BRAKE USAGE INFO ONCE AN ACFT HAS BEEN SWITCHED TO THE NEWER TYPE BRAKES AND TIRES. THIS SAME PROB EXISTS FOR THE B737-200 BRAKE ASSEMBLY. THE B737-400 AND -200 IN THE PAST; USED THE SAME BRAKES; BUT NOW THE -200 ACFT USES A NEW STYLE BRAKE WHICH IS DIFFERENT FROM THE BRAKES ON THE B737-400.