What was found
LOG PAGE 108434. DISCREPANCY: BOTH TRANSPONDERS MODE "C" ALTTITUDE REPORTING INOPERATIVE, C/B's RESET, NO HELP. AIRCRAFT RETURNED TO KMIA AND LANDED OVERWEIGHT UNEVENTFULL. CORRECTIVE ACTION: REMOVED AND REPLACED BOTH #1  ATC TRANSPONDERS IAW MM 34-53-0 ACCOMPLISHED TEST IAW FAR 43 APPENDIX"E" AND "F", PARAG "G" AND MM-34-53-0, ALL COVERS AND FLAGS REMOVED AFTER TEST. ACCOMPLISHED OVERWEIGHT LANDING INSPECTION "A" IAW ARROW AIR J/C 6372, NO DEFECTS NOTED. AIRCRFAT RETURNED TO SERVICE.