What was found
DURING SCHEDULED FLIGHT ON FINAL APPROACH (VREF107) WHEN CROSSING THE THRESHOLD, NR 4 ENGINE FLAMED OUT. ESP FOLLOWED. QRH REVIEWED AFTER LANDING. INSPECTED NR 4 ENGINE INTAKE & EXHAUST; NO EVIDENCE OF DAMAGE. SUMPED NR 4 FUEL TANK; NO CONTAMINATION FOUND. INSPECTED FUEL SYSTEM; FOUND FUEL HEATER DIRTY AND WATER CONTAMINATION. CLEANED & REINSTALLED FUEL HEATER STRAINER FILTER. PERFORMED POWER CHECK ENGINE RUN; OPS CHECKED NORMAL.