C172 FLOAT PLANE MAKES UNEVENTFUL WATER LNDG AFTER ENG FAILURE DUE TO WATER CONTAMINATED FUEL.

Narrative

THE ENG ON A CESSNA C172-XP FLOAT PLANE FAILED ON SHORT FINAL FOR LNDG ON LAKE. THE ACFT WAS AT APPROX 200 FT AGL; OVER THE LAKE; WHEN THE ENG STOPPED. STUDENT PLT AND INSTRUCTOR ABOARD. THE STUDENT MADE A SUCCESSFUL ENG-OUT LNDG. THERE WAS NO DAMAGE TO THE PLANE; NOR INJURIES TO OCCUPANTS. THE PROB WAS CAUSED BY WATER IN 1 FUEL TANK WHICH WAS NOT DETECTED DURING THE PREFLT INSPECTION. DURING THE PREFLT; THE INSTRUCTOR FOUND THE R FUEL CAP LOOSE AND ONLY PARTIALLY SEATED. A HVY RAINSTORM HAD DROPPED 5+ INCHES OF RAIN ON THE AIRPLANE AFTER ITS PREVIOUS FLT AND SO THE INSTRUCTOR AND STUDENT WERE CONCERNED ABOUT WATER IN THE FUEL. HOWEVER 4 FULL SAMPLES FROM THE TANK REVEALED NO WATER. CONCLUDING THAT THE TANK HAD NO WATER THE INSTRUCTOR ELECTED TO FLY. APPROX 1 HR INTO THE FLT; THE ENG STOPPAGE OCCURRED. AFTER LNDG; THE PLTS SAMPLED BOTH TANKS. THE R TANK HAD WATER. IT WAS NECESSARY TO SWITCH TO THE L TANK AND DRAIN THE GASOLATOR FOR 2-3 MINS BEFORE THE ENG COULD BE RESTARTED. THE ENG STOPPAGE WAS CAUSED BY AN INADEQUATE PREFLT INSPECTION. AFTER FINDING THE OPEN R TANK; THE PLTS SHOULD HAVE REQUESTED THAT THE TANK BE DRAINED. THE INSTRUCTOR INCORRECTLY RELIED ON A BELIEF THAT ANY WATER WOULD BE REVEALED BY SUMPING THE TANK 3 EXTRA TIMES. THE FLOAT PLANE SITS NOSE LOW WHEN STORED ON THE GND. THE SUMPS ARE AT THE BOTTOM REAR OF THE TANKS AND SO; EVIDENTLY; WATER CAN BE TRAPPED FORWARD IN THE TANK AND NOT BE DISCOVERED BY SUMPING WITHOUT RAISING THE NOSE.