PLT OF C172 EXPERIENCES LOSS OF PWR IN TFC PATTERN AS A RESULT OF FUEL CONTAMINATION WITH WATER. LANDS SAFELY.

Narrative

THE FLYING CLUB ACFT HAD BEEN PARKED ON AN OPEN RAMP WITHOUT THE ENG BEING STARTED FOR SEVERAL DAYS DURING WHICH TIME RAIN ALTERNATED WITH FREEZING AND NEAR-FREEZING TEMPS BEFORE THIS FLT ON A COLD; NO WIND VFR DAY. DURING PREFLT; 5 OR 6 SAMPLES OF FUEL FROM THE PORT WING TANK SHOWED WATER IN THE BOTTOM OF EACH SAMPLE. AT THAT POINT; I ROCKED THE WINGS AND THEN CONTINUED TO TAKE SAMPLES FROM THAT TANK UNTIL ABOUT THE 10TH SAMPLE DID NOT PRODUCE WATER. THE FIRST SAMPLE DRAWN FROM THE STARBOARD SHOWED WATER BUT THE SECOND SAMPLE DID NOT. THE LOWER SUMP WAS ALLOWED TO DRAIN DIRECTLY ONTO THE RAMP FOR SEVERAL SECONDS BEFORE A SAMPLING CUP WAS INTRODUCED INTO THE STREAM OF FUEL. SEVERAL SAMPLES WERE TAKEN; THE LAST SHOWING CLR OF WATER. THE AIRPLANE WAS FLOWN IN THE LCL AREA OF THE ARPT FOR ABOUT 1.2 HRS ON THE HOBBS METER WHEN; AFTER DOING A TOUCH-AND-GO; THE ENG SPUTTERED AS I TURNED DOWNWIND FOR A FULL STOP LNDG. I IMMEDIATELY LANDED ON THE NEARLY 'XWIND' RWY. THERE WAS MORE ENG SPUTTERING DURING TAXI IN TO THE RAMP. AFTER TAXIING TO PARKING AND ENG SHUTDOWN; BOTH WING TANKS WERE SAMPLED WITH NO WATER INDICATED. HOWEVER; 5 SAMPLES DRAWN FROM THE LOWER SUMP SHOWED ONLY OR MOSTLY WATER. I WROTE UP THE PROB AND ASKED THE DISPATCH CLERK TO GND THE ACFT. THEN I DISCUSSED THE MATTER DIRECTLY WITH THE MAINT PEOPLE. MAINT LATER RPTED THAT A CONSIDERABLE QUANTITY OF WATER WAS SUBSEQUENTLY DRAINED FROM THE SYS. ONE FUEL TANK CAP WAS REPLACED. WHEN SEVERAL EARLY SAMPLES SHOW MORE THAN A MINOR AMOUNT OF WATER; IT SHOULD NOT BE ASSUMED THAT LATER SAMPLES IN A SERIES WHICH ARE CLR OF WATER NECESSARILY MEAN THAT ALL OF THE WATER HAS BEEN PURGED FROM THE SYS. WHEN SEVERAL SAMPLES SHOW WATER; LARGE QUANTITIES SHOULD BE DRAINED FROM ALL THE ACFT'S SUMPS TO ASSURE NON-CONTAMINATION.