PA18 PLT FEARS LOSING ENG AND FLIES UNDER BRIDGE.

Narrative

PLT WAS RECEIVING FLT FOLLOWING. PERMISSION WAS GRANTED TO FLY DOWN THE RIVER. ATC SAID; IF YOU INTEND TO FLY S OF THE CENTER OF THE RIVER; LET US KNOW FIRST. PLT INTENDED TO FLY DOWN THE RIVER WHICH WOULD HAVE INCLUDED GOING OVER THE HUGE SUSPENSION BRIDGE -- WHICH SHOULD NOT HAVE BEEN A PROB. HOWEVER; SUDDENLY PLT FELT THE ENG WAS ACTING STRANGE AND PWR WAS BEING REDUCED. PLT OPTED TO FLY UNDER THE BRIDGE TO PROVIDE TIME TO ASSESS THE SITUATION AND DID NOT WANT TO RUN THE RISK OF ENDING UP DIRECTLY OVER THE BRIDGE AND HAVE THE ENG QUIT. HEADING N WAS AN OPTION; HOWEVER; IN THE HEAT OF THE MOMENT; PLT HAD IN HIS BRAIN THAT HE HAD TO STAY OVER THE RIVER (DUE TO ATC INSTRUCTIONS) -- SO UNDER THE BRIDGE WAS THE DECISION MADE. ALSO IN THE HEAT OF THE MOMENT; ENG PWR WAS THE MOST IMPORTANT ISSUE AT HAND. PLT SWITCHED TANKS. PLT MOVED MIXTURE TO FULL RICH WHILE DSNDING TO GET BETTER POSITIONED TO SAFELY GO UNDER THE BRIDGE. CARB HEAT WAS ALSO TURNED ON. SINCE IT WAS A CONGESTED AREA; THE RIVER WOULD HAVE BEEN THE BEST OPTION ANYWAY IF THE ENG DID STOP. POSSIBLE CAUSES: TANKS NEEDED TO BE SWITCHED. THE PA18 HAS A L/R TANK SELECTOR. NO 'BOTH' SETTING. MIXTURE SETTING MIGHT HAVE LED TO THE ENG ISSUE. CARB ICE COULD HAVE CONTRIBUTED. PLT HAD A NOISE CANCELLATION HEADSET AND WHEN THE BATTERIES GO DEAD; THINGS GET NOISY AND SOUND DIFFERENT; SO IT IS POSSIBLE THIS WAS A FACTOR IN MAKING IT SOUND LIKE THE ENG WAS LOSING PWR. THROTTLE ON XCOUNTRY FLTS HAS BEEN KNOWN TO BLEED DOWN. THIS ISSUE WAS FIXED RECENTLY; SO IT'S POSSIBLE THE THROTTLE JUST SLIPPED BACK SOME AND SPOOKED THIS PLT. UPON COMING OUT OF THE OTHER SIDE OF THE BRIDGE; THE AIRPLANE CLBED UP TO ALT AND PROCEEDED ON COURSE WITH NO FURTHER DIFFICULTIES.