SHORTLY AFTER DEP FROM BDE; PLT OF FLOAT EQUIPPED C180 EXPERIENCES AN INCREASING LOSS OF PWR. CHOOSES TO LAND OFF ARPT TO AVOID DETERIORATING TERRAIN CONDITIONS.

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I HAD DEPARTED BDE AND HEADED SW. AFTER ABOUT 10 OR 12 MINS MY ALT SAGGED A BIT. I TRIMMED UP AND THEN BEGAN TO LOSE AIRSPD A BIT. IT WAS OBVIOUS THE ENG WAS LOSING PWR. I WENT THROUGH ALL THE STANDARD CHKS BUT NOTHING HELPED AND COULD NOT MONITOR ALT OR AIRSPD. WE WERE ON THE EDGE OF THE 'BOG' AT ABOUT 600 FT AND I MADE A DECISION TO MAKE A PRECAUTIONARY LNDG RATHER THAN GO ON OVER THE TREES AND HAVE A SERIOUS WRECK. I COMMUNICATED THIS TO THE PLANE I WAS TALKING TO AND PROCEEDED TO CIRCLE INTO THE WIND; EXTEND THE FLAPS TO 2 NOTCHES AND I PUT IT ON WITH NO INCIDENT OF ANY KIND. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: 'THE PLT; A SEASONED VETERAN OF NUMEROUS DECADES' EXPERIENCE TOLD AN INTERESTING STORY ABOUT THE EVENTS. THE LOCATION ON WHICH HE OPTED TO LAND WAS WHAT HE TERMED A 'BOG' AREA; COVERED GENERALLY WITH A FEW INCHES OF WATER WITH OCCASIONAL AREAS WHERE IT WAS WAIST DEEP. THUS THE TOUCHDOWN WAS TECHNICALLY ON WATER. HE STATED THAT ALTHOUGH HE HAD SIGNIFICANT EXPERIENCE IN SIMILAR ACFT TYPES; THEY HAD ALL BEEN PWRED BY FUEL INJECTED ENGS. THE APPARENT CAUSE OF THE PWR LOSS WAS THE RESULT OF CARB ICING. SINCE FUEL INJECTED ENGS ARE NOT SUSCEPTIBLE TO THE EFFECTS OF CARB ICE; HE WAS UNFAMILIAR WITH THE SYMPTOMS. WITH THE CONSTANT SPD PROP THE RPM DOESN'T DROP AS IT DOES WITH A FIXED PITCH PROP ON A CARBURETED PWR PLANT. THE LOSS OF AIRSPD AND INABILITY TO MAINTAIN ALT WAS THE RESULT OF THE ICE BUILDUP IN THE CARB RESTRICTING AIRFLOW TO THE ENG. ALTHOUGH HE USED THE CARB HEAT MOMENTARILY; HE STOPPED DUE TO THE PWR LOSS (A NORMAL RESULT OF THE INCREASED TEMP OF THE AIR TO THE ENG) ASSOCIATED WITH TURNING It ON. HAD HE LEFT THE CARB HEAT ON; THE PROB WOULD HAVE DISSIPATED IN A MATTER OF SECONDS AND THE FORCED LNDG WOULDN'T HAVE BEEN NECESSARY.