What was found
BWI - FL 209 - AFTER T/O, INFORMED TIRE DEBRIS WAS ON RUNWAY AFTER T/O. DURING PREP FOR LANDING, THE LT MAIN GEAR RED UNSAFE LIGHT ILLUMINATED. AFTER TWO FLYBYS, TOWER DETERMINED GEAR DOWN WITH SOME DEBRIS BETWEEN LEFT MAIN TIRES. F/O MADE VISUAL INSPECTION THRU MAIN GEAR VIEWER. CAPT DECLARED EMERGENCY AND THE FLT LANDED W/O INCIDENT. AFTER LANDING, MAIN GEAR WAS PINNED AND A/C TAXIED TO GATE. MX FOUND TREAD SEPARATED FROM THE LT MAIN GEAR INBD TIRE, CAUSING DAMAGE TO THE LT MAIN GEAR UPPER DOWNLOCK ASSY AND THE LT INBD T/E AFT FLAP. REPLACED DOWNLOCK ASSY, AFT FLAP AND WHEEL/TIRE ASSY (P/N 6558256275). GEAR TEST AND OPS CHECK NORMAL. (M)