SMA PLT PRACTICING TOUCH-AND-GO LNDGS HAS ENG QUIT ON TKOF. OFF FIELD LNDG.

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IT WAS AN OVCST DAY. TEMP HOVERING AROUND FREEZING. THERE WAS NO VISIBLE MOISTURE IN THE AIR; BUT THERE WAS NO DOUBT A NARROW MARGIN BTWN DEWPOINT AND TEMP. MY INTENT WAS TO STAY IN THE TFC PATTERN PRACTICING TOUCH-AND-GOES IN HIGH WING/TRICYCLE. AFTER THE CUSTOMARY PREFLT; I TAXIED OUT FOR DEP. THE STANDARD BEFORE TKOF CHKLIST WAS PERFORMED. THE STATIC RUN-UP AND CARB HEAT CHK AT 1700 RPM INDICATED NO REASON TO BE CONCERNED. ON THE DOWNWIND LEG I APPLIED FULL CARB HEAT BEFORE THROTTLE BACK. THERE WAS NO INDICATION OF ENG ROUGHNESS OR ANY LOSS OF RPM. AFTER TOUCHING DOWN; I PROCEEDED TO RETRACT FLAPS; CLOSE CARB HEAT AND APPLY FULL THROTTLE. I CLBED TO 500 FT MSL WHEN WITHIN A TIME SPAN OF ABOUT 5 SECONDS I DETECTED A LOSS OF RPM AND SUDDENLY THE ENG QUIT. PRIMER; IGNITION; THROTTLE; MIXTURE ALL CHKED OUT. I WAS ABLE TO MAINTAIN BEST GLIDE AND SET DOWN ON A NEARBY HWY. THE LNDG WAS OTHERWISE UNEVENTFUL. AFTER BEING TOWED BACK TO THE ARPT; INSPECTION AND TEST FLT ALL PROVED NEGATIVE. CONCLUSION WAS CARB ICING HAD OCCURRED. I HAD ALWAYS BEEN TAUGHT THAT CARB ICE AT FULL PWR IS NOT OF CONCERN. AFTER READING A NUMBER OF ARTICLES RECENTLY ON THIS TOPIC; I HAVE CONCLUDED THAT CARB ICE CAN OCCUR VERY QUICKLY GIVEN THE RIGHT METEOROLOGICAL CONDITIONS EVEN AT FULL PWR. IN THE FUTURE I WILL CLOSELY MONITOR THE DEWPOINT/TEMP SPREAD. I WILL ALSO BE READY TO RESPOND FASTER WITH CARB HEAT AT THE FIRST SIGN OF RPM SLIPPAGE; EVEN IF AT FULL PWR. AND; WHEN IN DOUBT I WILL TRADE OFF TOUCH-AND-GOES FOR FULL STOP LNDGS; RECHKING ENG RUN-UP EACH TIME OR BETTER YET; STAY ON THE GND AND WAIT FOR A BETTER DAY TO FLY.