Narrative:

My students and I were on our final leg of our long IFR cross country. We left for ZZZ1 via ZZZ for the GPS runway approach into ZZZ. Planned on the missed and on home to ZZZ1. WX forecast for snow to start in this area and ZZZ1 around XC00. We encountered snow about XA30 about 1/2 way to ZZZ. We were controled by approach controller. The closer to ZZZ the heavier the snow. I turned on pitot heat. We started our first vectors onto the approach and I pulled the pitot heat to see if anything was building up -- no signs of ice etc. I have never used pitot heat on the cherokee like I do in a cessna. We shot the approach down to the MDA and never saw any signs of the ground. We executed the missed/climb out instructions given by approach controller. Soon thereafter in the climb we were losing power. I immediately checked that the fuel primer was in; fuel pump was already on; and flowed to the carburetor heat lever. When pulled; the engine almost died. With my altitude as it was; I decided to turn off the carburetor heat and keep what motor I had left -- better glide ratio were my thoughts at the time. I contacted approach and told them I had a motor problem. I can't remember the exact dialogue; but told them I needed vectors to a clear area or the airport. They offered me the ILS but told them I could not sustain altitude and they gave me turns back to the airport. I zoomed in the garmin 430 and had enough altitude to get back to ZZZ with an uneventful landing. Although the motor was almost ready to die I was able to taxi back to the ramp and drove home to ZZZ1. Was never able to run the motor up to try and clean up with carburetor heat as the pavement was icy at ZZZ and could not stay in one spot. I told the mechanics about it at ZZZ1 and for sure it was carburetor icing -- their opinions. I have given a statement to the local FSDO with this information last week. Thought I was ok; but everybody told me to send in a NASA report so here it is. Hope this helps. I have since talked to a lot of different people and all of us seem to be on the same page as how we have used carburetor heat on a cherokee -- obviously we aren't doing the right thing. My procedures have changed after this experience!

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Original NASA ASRS Text

Title: A PA28 INSTRUCTOR NEW TO THE ACFT TYPE; USED CARB HEAT INCORRECTLY IN SNOW AND COLD NEARLY CAUSING THE ENG TO QUIT DURING A GAR.

Narrative: MY STUDENTS AND I WERE ON OUR FINAL LEG OF OUR LONG IFR XCOUNTRY. WE LEFT FOR ZZZ1 VIA ZZZ FOR THE GPS RWY APCH INTO ZZZ. PLANNED ON THE MISSED AND ON HOME TO ZZZ1. WX FORECAST FOR SNOW TO START IN THIS AREA AND ZZZ1 AROUND XC00. WE ENCOUNTERED SNOW ABOUT XA30 ABOUT 1/2 WAY TO ZZZ. WE WERE CTLED BY APCH CTLR. THE CLOSER TO ZZZ THE HEAVIER THE SNOW. I TURNED ON PITOT HEAT. WE STARTED OUR FIRST VECTORS ONTO THE APCH AND I PULLED THE PITOT HEAT TO SEE IF ANYTHING WAS BUILDING UP -- NO SIGNS OF ICE ETC. I HAVE NEVER USED PITOT HEAT ON THE CHEROKEE LIKE I DO IN A CESSNA. WE SHOT THE APCH DOWN TO THE MDA AND NEVER SAW ANY SIGNS OF THE GND. WE EXECUTED THE MISSED/CLBOUT INSTRUCTIONS GIVEN BY APCH CTLR. SOON THEREAFTER IN THE CLB WE WERE LOSING PWR. I IMMEDIATELY CHKED THAT THE FUEL PRIMER WAS IN; FUEL PUMP WAS ALREADY ON; AND FLOWED TO THE CARB HEAT LEVER. WHEN PULLED; THE ENG ALMOST DIED. WITH MY ALT AS IT WAS; I DECIDED TO TURN OFF THE CARB HEAT AND KEEP WHAT MOTOR I HAD LEFT -- BETTER GLIDE RATIO WERE MY THOUGHTS AT THE TIME. I CONTACTED APCH AND TOLD THEM I HAD A MOTOR PROB. I CAN'T REMEMBER THE EXACT DIALOGUE; BUT TOLD THEM I NEEDED VECTORS TO A CLR AREA OR THE ARPT. THEY OFFERED ME THE ILS BUT TOLD THEM I COULD NOT SUSTAIN ALT AND THEY GAVE ME TURNS BACK TO THE ARPT. I ZOOMED IN THE GARMIN 430 AND HAD ENOUGH ALT TO GET BACK TO ZZZ WITH AN UNEVENTFUL LNDG. ALTHOUGH THE MOTOR WAS ALMOST READY TO DIE I WAS ABLE TO TAXI BACK TO THE RAMP AND DROVE HOME TO ZZZ1. WAS NEVER ABLE TO RUN THE MOTOR UP TO TRY AND CLEAN UP WITH CARB HEAT AS THE PAVEMENT WAS ICY AT ZZZ AND COULD NOT STAY IN ONE SPOT. I TOLD THE MECHS ABOUT IT AT ZZZ1 AND FOR SURE IT WAS CARB ICING -- THEIR OPINIONS. I HAVE GIVEN A STATEMENT TO THE LCL FSDO WITH THIS INFO LAST WK. THOUGHT I WAS OK; BUT EVERYBODY TOLD ME TO SEND IN A NASA RPT SO HERE IT IS. HOPE THIS HELPS. I HAVE SINCE TALKED TO A LOT OF DIFFERENT PEOPLE AND ALL OF US SEEM TO BE ON THE SAME PAGE AS HOW WE HAVE USED CARB HEAT ON A CHEROKEE -- OBVIOUSLY WE AREN'T DOING THE RIGHT THING. MY PROCS HAVE CHANGED AFTER THIS EXPERIENCE!

Data retrieved from NASA's ASRS site as of May 2009 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.