Carb Heat: What's the deal?

[thing]

You should see a definite drop of at least 150 RPM drop when carb heat is selected on.

That's interesting, our 28 drops about 30 rpm when carb heat is selected. I've checked the linkage to the box, all seems in order. I haven't checked inside the box. General consensus is that 'it just does that.' I have had carb icing in that particular a/c and applying carb heat cleared it.

[Pull what]

If you are at cruise flight power and you get carb ice, selecting carb heat without adding power will still get more then enough heat into the engine to melt the ice.

I am sure you are right but carb icing isnt just going to occur in just one spot in the sky especially if you are level. There are two stages to managing the threat.
1 Is to remove the ice
2 Is to stop it forming again

Selecting full power makes it less likely to form again. Someone mentioned a problem if you are leaned-well carb heat enriches the mixture so that will not be a problem and in fact continuing with step two is in fact to lean the mixture if you need to run with carb air hot to stop further icing.

I note our C152 manual says also carb air hot & select full power as indeed does the CAA safety sense leaflet, or it certainly encourages the use of full power.

[Big Pistons Forever]

Pul what

I do not think you have convinced me but I am sure not going to say you are wrong. There is no doubt that carb heat on with full power will produce the most amount of hot air and if any doubt this is the safest action.

My only point of debate is whether this should be the universal automatic practice anytime carb ice is suspected. I personally do not think so but this issue like many others will have more than one "right" answer

[Big Pistons Forever]

I just got the May addition of Pilot on my i-pad. I always make a point of reading
the "Safety Matters" column which IMO is an excellent learning opportunity for every pilot, no matter what their experience.

The second accident profile was a Pa 28 that was forced landed after an engine failure. Since the engine was subsequently tested with no faults found, the flight was on December 27 and thus with a temp and humidity doubtlessly smack in the middle of the severe carb icing range, and the engine reportedly sputtered and refused to accelerate after a low powered descent, it is pretty hard not to conclude that carb ice was the most probable cause for the failure. And carb ice is totally preventable by the pilot.

If the engine does get a big dose of carb ice the engine will initially sputter as soon as the heat takes effect because of the thawed ice water going through the engine. The carb heat must be left on sufficiently long to clear the ice which may require up to 20 to 30 seconds of heat.

The good news was a successful forced landing was carried out with no injuries although the aircraft was heavily damaged. The pilot reported that he attributed his success to "frequent forced landing practice" which leads me to wonder if he had used some of that practice time to learn and practice how to keep the engine from failing in the first place the requirement to use all that forced landing practice for real, might have been avoided......