What was found
(CAN) AIRCRAFT FLEW IN RAIN APPROXIMATELY 45 MINUTES, AND THEN CAME OUT IN THE CLEAR AT 7,000 FEET, AND -5 DEGREES CELSIUS. ENGINES FUEL FLOW DECREASED, ENGINES SLOWED DOWN. PILOT SELECTED ALTERNATE AIR ON AND RECOVERED POWER. RE-SELECTED ALTERNATE AIR OFF AFTER A FEW MINUTES AND TERMINATED FLIGHT NORMALLY. BOTH ENGINES' AIR INTAKE FILTER ELEMENTS P/N BA15 FOUND SATURATED WITH WATER. SUBMITTER SUSPECTED WET ELEMENTS FROZE UP RESTRICTING AIRFLOW.