Date: 201604
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: M-7
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Training
Flight phase: Landing
Reporter organization: Personal
Reporter function: Instructor; Pilot Not Flying
Reporter qualification: Flight Crew Flight Instructor; Flight Crew Flight Engineer; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Sea; Flight Crew Multiengine
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Other / Unknown; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Crew
When detected: In-flight
Contributing factors: Aircraft; Human Factors; Procedure
Primary problem: Procedure

Narrative: We were flying south from our home base and after we had been flying slightly over an hour; we had done a landing on a lake and in the process of doing the second landing on that same lake when all of a sudden during the landing on water; the engine quit. The propeller stopped and aircraft came to a stop on the lake without incident or any damage. We tried one unsuccessful restart while on the water without success. Since we were well out into the large lake; approximately 2 miles from the north shore; with south wind blowing us that way; we sailed the seaplane backwards and decided to call the Sheriff's office on our cellphone to see if there was anyone who could tow us to shore. The County Sheriff's office contacted [Fish and Wildlife Service] and within 10-15 minutes; a boat arrived at our location in the middle of the large lake to assist us. I boarded the boat and left the seaplane floating with the other pilot still aboard the stranded seaplane. We went north to the shoreline to see if we could find a safe haven to tow the seaplane so that repairs could later be effected. We discovered a very good safe haven and spoke with the homeowner there to ask if it would be ok to tow the disabled seaplane there. The homeowner was helpful and replied affirmatively. We went back to the drifting seaplane which was headed that way on its own due to moderate south wind. We towed the disabled seaplane to the north shore and then waited for our FAA A&P/IA to arrive. We had noticed fuel dripping from the carburetor area so we secured the fuel by switching the fuel selector off. The mechanic removed an apparently faulty carburetor and he secured the seaplane before leaving.The next day I took the faulty carburetor to a carburetor repair man. The repair man reported to me that the carburetor; although looking good from the outside; was mostly filled with very rusty water and had a cheap white plastic float that should have been replaced a long time ago. He said it was one of the worst situations he had ever seen and he wasn't yet certain that he could fix it. It was caused by unpure fueling system that we formerly had used to fuel seaplanes; a system without adequate filtering or water prevention.Long story short; nothing happened; no damage! However; had this engine failure occurred in a situation where we had no safe landing alternative; this NASA Safety Report would instead likely be an NTSB Aircraft Accident Report; likely at a minimum with major seaplane damage and possibly severe injury or death i.e. this was a close call! We will in the future ensure that not only our fueling system will be debris and water free; but will do our best to disseminate our story to other home fuelers. Murphy's Law was apparently taking a vacation on this day.




Synopsis: M7 seaplane instructor reported the engine quit on landing while doing touch and goes. Fault was due to carburetor fuel contamination.