Narrative:

I left ZZZ about XA00 on sep/wed/04. There were some cumulous clouds to the northwest, not large, nor was I aware of any thunder or lightning. I made 3 lndgs and takeoffs on the lake. Then I landed, turned off the engine, relaxed and ate a sandwich. After 15 mins, I started the engine, set it at idle, and started through my checklist, when a tremendous blast of wind hit me with no warning. I watched in amazement as the left float was pushed down underwater and right wing went up and up. The aircraft turned slowly completely over. I opened the door after unblocking my harness and swam out. 2 men onshore saw that the aircraft had disappeared. They called 911 and then came out in a boat. Soon after the sheriff's boat and coast guard arrived and took me on board. The aircraft did not sink, but remained under water suspended by the floats. The problem arose from being on the water in the vicinity of a thunderstorm. The 2 men who rescued me estimated winds at 70 mph. The right decision would have been to not land on the lake at all with cumulous clouds anywhere in the vicinity.

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Original NASA ASRS Text

Title: PLT OF EXPERIMENTAL AMPHIBIOUS FLOAT PLANE, AT IDLE TAXI ON HIGH ALT LAKE, IS OVERTURNED BY GUST FRONT ASSOCIATED WITH DISTANT CONVECTIVE ACTIVITY.

Narrative: I LEFT ZZZ ABOUT XA00 ON SEP/WED/04. THERE WERE SOME CUMULOUS CLOUDS TO THE NW, NOT LARGE, NOR WAS I AWARE OF ANY THUNDER OR LIGHTNING. I MADE 3 LNDGS AND TKOFS ON THE LAKE. THEN I LANDED, TURNED OFF THE ENG, RELAXED AND ATE A SANDWICH. AFTER 15 MINS, I STARTED THE ENG, SET IT AT IDLE, AND STARTED THROUGH MY CHKLIST, WHEN A TREMENDOUS BLAST OF WIND HIT ME WITH NO WARNING. I WATCHED IN AMAZEMENT AS THE L FLOAT WAS PUSHED DOWN UNDERWATER AND R WING WENT UP AND UP. THE ACFT TURNED SLOWLY COMPLETELY OVER. I OPENED THE DOOR AFTER UNBLOCKING MY HARNESS AND SWAM OUT. 2 MEN ONSHORE SAW THAT THE ACFT HAD DISAPPEARED. THEY CALLED 911 AND THEN CAME OUT IN A BOAT. SOON AFTER THE SHERIFF'S BOAT AND COAST GUARD ARRIVED AND TOOK ME ON BOARD. THE ACFT DID NOT SINK, BUT REMAINED UNDER WATER SUSPENDED BY THE FLOATS. THE PROB AROSE FROM BEING ON THE WATER IN THE VICINITY OF A TSTM. THE 2 MEN WHO RESCUED ME ESTIMATED WINDS AT 70 MPH. THE RIGHT DECISION WOULD HAVE BEEN TO NOT LAND ON THE LAKE AT ALL WITH CUMULOUS CLOUDS ANYWHERE IN THE VICINITY.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.