We had the engine stop in our PA28-180 on short final when the pilot failed to use carb heat. On checking the graph in the attached CAA notice, he was in prime icing conditions.
https://publicapps.caa.co.uk/docs/33/20130121SSL14.pdf
20130121SSL14_pdf
It’s when things becomes irrelevant that we make all sort of arguments 
I pull carb heat when I throttle back, I push it when I go full power as the associated hand mouvement with two fingers is natural…
Carb heat & flaps & mixture are those things that fall under “as necessary or as required” in the checklists, there are two schools: 1/ those who will teach you to always leave this way as not to forgot and 2/ those who will teach to use it as necessary: in my aeroclub, the SOP is to fly with mixture full rich all the time and set carb heat HOT on descent and set carb heat COLD at 100ft agl ready for the go-around, irrespective of conditions, my understanding the end goal is to make sure “people do not to forget it” NOT “make good use of it”
I can see there’s just as much debate and just as little consensus here as there is anywhere else. I think I’ll stick to my habit of carb heat when reducing power for descent in the circuit, then turning it off on rollout or go around. I don’t hear any real downsides to doing so.
skydriller wrote:
you can SEE the humidity…
Sure, but the question is if the temperature drop in the carburettor is large enough to form ice when the OAT is +30°C.
The FAA state carb ice cannot occur above 25C.
Have they not flown out of Galveston in the summer then?? 30+degC and you can SEE the humidity…
Regards, SD..
My practice has depended a lot on the engine and installation. When learning to fly my Luscombe I learned quickly to turn on carb heat a little bit before reducing power because the little Continentals are renowned ice makers and the carb heat airbox was not that big. Once you had the carb good and warm, the power could be reduced and nothing bad would happen. On a go around, your right hand could push throttle open and carb heat off in one motion, and everything went well.
On my current plane with an O-320 Lycoming,
the manufacturer guidance is to use “as required” and I’ve learned that it’s rarely necessary. The only time I’ve had carb ice is when taxiing out with a cold engine, before takeoff. I’ve never had symptoms of carb ice in flight and don’t typically use carb heat for approach in my warm climate.
I was taught to apply carb heat on reducing power to descend, and to close it after landing. That was at Inverness EGPE on a C152. It was not required when checked out on a C150 at Grand Junction KGJT in July – west of the Rockies.
Later I changed to closing it at 2 -300’ on our Jodel DR1050, with O200, – until after landing at Broadford , Skye, the engine almost stopped when I opened the throttle to turn and backtrack, If it had been a go-around, it could have been a disaster.
The FAA state carb ice cannot occur above 25C. The Canadian CAA disagree, and say with mogas it can occur at any temp. I now start the take-off roll with carb heat on if carb ice is likely, closing it as I reach full power. I also do this when below carb ice temp with a wet deiced runway.
I’ve has several power losses and engine stoppages, but always with enough runway to land or stop. All in the Jodel with O200 and Mogas, none with Avgas and O200 in the Bolkow Junior. But frequent stoppages in both immediately after starting a cold engine. Assumed to be carb ice as carb had frost on the outside in cases where it was quickly looked at.
The answer to that is, get a carb heat gauge and see what happens. You might be surprised.
Once again I agree with @Skydriller. I hope this doesn’t become a habit🙂
I was reading an old Info PIlote the other day at the club and it was about the high percentage of accidents and hard landings due to expected carb icing.
This was the compounded when doing touch and goes which carb icing was expected to have formed during the approach and landing and had not cleared when the carb heat was returned to cold and full power applied, ending in an EFATO.
To my knowledge setting full power with carbheat ON may lead, depending on OAT / density altitude, to detonation, i set carbheat always to OFF in short final.
