Carb Heat Demystified: Understanding the mechanics and the dangers

Season 3, Episode 2

One of the oldest debates in aviation, and something that's received so many comments on my channel that I have a copy-pasted answer... Everyone seems to have different rules about when to use carb heat, but the answer might not be so simple. Find out what exactly happens when you engage carb heat, and what that means for your engine. As always, I am only a pilot sharing my thoughts on the industry. Only a licensed flight instructor can provide advice on aircraft operation, so befriend one as quickly as you can!

Hey, did you guys know that the FAA actually certifies flight instructors to tell you everything that I try to convey in these videos? You should definitely talk to one of them instead of trusting some video you found on the internet, because who am I to tell you how to fly? I'm just a pilot sharing my experiences with the world, and these videos are not meant to be instructional or advisory in any respect.

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[Virtualmix]

Basically, do what the POH says.
I worked a few years as a mechanic and I never heard of an airplane engine being damaged because of carb heat use. On the other hand, I've read countless accident reports, sometimes deadly, resulting from pilots not using carb heat when they should have.

[ChrisHumphrey]

This was interesting to watch. I have no aeronautical background but I’ve been told that my grandfather invented carburetor heat. This was the first time I’ve understood what it was. He was an aeronautical engineer in the 40’s and 50’s.

[alexmelia]

I learned to fly on Cessna's and transitioned to Pipers. I found the complete 180 of use of carb heat perplexing. I did some research and found some interesting items.

During the 1960s, accidents were VERY commonplace. Go do a search during the late 60s and you'll find about upwards of 60 a month. That's about 2 per day. Granted it was the heyday of aviation and all manufacturers were pumping out astounding numbers of planes, but it seems that training was not quality controlled as it is today. It's interesting to note that in the early 60s, the Owners Manual (good luck getting a quality POH back then) was little more than advertising typed up by lawyers. This is evident by Cessna's switch from Continental to Lycoming engines, they retained the requirement of the use of carb heat, even though the Lyc is much less prone to it. They determined it would pose less risk to the company.

Piper's lawyers, on the other hand, felt as if the lack of power on go around was reason enough to mitigate using carb heat and as such, recommend you NOT to use it. But do a search on Cherokee crashes. At my home field, we've had three fatal accidents in the past 30 years. Two of which were Piper Cherokees. Both had unexplained power loss. Conditions at the time were favorable to carb icing. One survivor in one of them admitted they pulled power for a long descent from cruise and at 1, 000 feet lost power. Applying carb heat was too little too late, the engine was too cold to melt. The aircraft crashed into terrain and the PIC died.

As denoted in the film, know how your carb heat works and make an informed decision. Using it proactively will not hurt you (unless you count sucking in unfiltered air, in which you would have to do A LOT to begin deteriorating the health of your engine) but it can help you.

Using carb heat on my last flight potentially saved my life. Normal run up, normal drop at 1600rpm with an application of carb heat. I went flying, and an hour later on return dropped my gear and put prop at full forward (2700rpm). Power 16" MP, I applied carb heat in the downwind and immediately lost a majority of power. Carb temp gauge was pegged in the plus (no ice) so I disengaged carb heat and all returned to normal. Carb temp still good. I landed and thought about the problem. Pulled the cowl, did some ground running and pulled the carb heat shroud. I found a crack in my exhaust, in which applying carb heat at high RPM sucked the exhaust into the intake causing an overly rich mixture and starving the engine. Note: IT DID NOT DO THIS ON THE GROUND AT LOW RPM. If I had continued to fly, the crack WOULD have propagated and I WOULD have suffered from CO poisoning. I have since sent my exhaust out for overhaul and purchased a digital CO monitor (I have the stick-on placard and it did not indicate ANYTHING).

So yes, carb heat possibly saved my life in an indirect fashion.

Just my $0.02. Not an A&P, PPL owner only.

[beagle]

I learnt to fly in the eighties, For those who insisted you didnt need Carb Geat on warm day, the Chief Flying Instructor who was anex airline pilot on the last piston days and early jet day took them up in a Cherokee on a clearr day the warmer the better. they never ran that argument again . He showed me too, I forget exactly what he did, but the engine nearly stopped. His command not advise always use Carb Heat if dercending, End Of Story!

[aviatortrevor]

"DO NOT USE CARB HEAT until you've seen this"

Welp... I'm going flying now. Can't watch your video until later. I guess I won't use carb heat until then XD

[emptypockets]

I only turn on carb heat if the ice on the wings is 1 inch thick or more.

[captainjohnh]

If you are flying one of the Cessna's that has the forward facing air filter, take some time to re-read the POH. You will likely find one sentence buried in the Expanded Normal Procedures that reads "The use of full carburetor heat is recommended during flight in very heavy rain to avoid the possibility of engine stoppage due to excessive water ingestion." (page 4-16 in the 152 manual).

It happened to a fellow CFI back in my instructing days at OMN.

[mytech]

Most cars from the late 70s through 80's had carb heat but the valve (thermostatic, not manual) was simply placed upstream of the air filter.

[mrdarkside]

Clicked on this because my hungry self thought it said Crab Meat. Not my proudest moment...

[jeffmarken]

In a Cessna 195, you apply carb heat in cruise to bring the carb temp gauge up to around 70 deg. F and it leans out much better. Also, in many airplanes in IMC and low power settings even still in green arc you might get icing (in the 195 I always keep the carb temp above the credit carat on the gauge when in the clouds). There are just never absolutes.

[IllFlyIt]

Green arc on a tach indicates no carb heat required?

Something I didn't know with 6, 000 hours total time. Always learning!

[NETBotic]

Be careful spewing all this logic online. I knew all of this stuff about carb heat but I watched because your videos are so well done. The graphical animations are sweet. I love flying fuel injected. I just switched flight clubs so I can fly a G1000 equipped, fuel-injected, C-172. If only I could get the engine started!

[MerryfaceAviation]

Awesome video! really good explanations. I would like to add though, that Lycoming themselves have said that on their O-320 engines, they were unable to purposefully induce detonation using carb heat. Here in the UK we teach to turn off Carb heat 200-400ft above touch down, and to turn on carb heat below the green arc (just like you said). We also turn carb heat in the circuit, somewhere late downwind. This is of course a generalization. As you said, the POH comes first! What is says goes.

[PilotSpOB]

From a KBED based student in the final weeks before the check-ride, good stuff. Keep up the great channel!

[scipioafricanus]

I really appreciate these informative videos with the terrific graphics.

[gevmage]

Fantastic explanation. I didn't know about the air intakes on Pipers being behind the cylinders; but I knew there was some fundamental difference between Pipers and Cessnas.

This was of course, a discussion of when to precautionarily use carb heat. One thing I think is left out of pilot training (that I'm aware of) is in what manner to apply carb heat when you're suspicious of carb ice. I went flying with a club C-150 one time when (apparently) the air was right in the middle of the carb ice butter zone. I built up significant carb ice at cruise power. That flight taught me a lot.

The thing that instructors don't stress enough (I think) is that if you think you might have carb ice, turn the carb heat full on, put throttle to FULL, and LEAVE them both that way for at least 30 seconds or a minute. If you do have carb ice built up, as it melts off from the carb heat, you'll get slugs of water going through the intakes causing the engine to sound terrible. You have to let it work, which might take a minute or two to completely clear out if you let it build up.

For the same reason, when I test carb heat in a Cessna, I turn it on and let it sit there for at least 15 seconds, to make sure that it's not already getting carb ice out. In the flight I mentioned above, I later realized I was probably building up ice while taxiing (at low throttle, of course) on the ground.

[WolfTangoFox]

Very informative video, Nick, well done! Being on the flight simulation side of things, these things are easy to neglect, yet may be hard to grasp. This video really brings it all together!

[Ichibuns]

Kind of makes you want the Piper over the Cessna. Will definitely add this to my research on individual planes

[ViprZ]

Very well put together! The most important reason us Cessna pilots use it though is because you will see power reduction when you get ice, and it will take some time to get that power back. That's not something you want in a critical phase of flight. Engines have been known to stop completely from carb ice. So you have to be especially mindful on very humid days.

[padiengel]

Was able to fly the PA28A the last two weeks. Made me think of your channel :) i used your videos for studying and preparing for the flights as I've never flown a plane before. Nice video! :)