What was found
MIA - FLT 657 - EN ROUTE JFK-PAP, DURING CRUISE, LEFT INNER FUEL QTY INDICATION RAPIDLY DECREASED FROM ABOUT 28,000 TO 11,500 LBS. NO FUEL LEAK INDICATION. AIR INTERRUPTED AND LANDED MIA WITHOUT INCIDENT. REPLACED FUEL QTY COMPUTER. PERFORMED ALL REQUIRED TEST CHECKS ACCORDING TO MAINTENANCE MANUAL. SUMPED ALL TANK OF WATER. TRANSFERRED ALL FUEL OUT OF LEFT INNER TANK, HAD FUELER METER FUEL BACK INTO TANK. USED FUEL TANK STICK FOR FUEL VERIFICATION. SYSTEM GROUND CHECKED NORMAL OPERATION. (M)