Carb heat - turn off short final

[Romeo Juliet Whiskey]

If the conditions are right, how quickly can one accumulate carb ice? I ask this question because it seems a common practice is to turn carb heat off on final approach in case of a go-around. Is this potentially a dangerous time to be turning carb heat off? And given that you only lose a few percent in engine power, would it make much difference in the go-around if you left carb heat on?

 

Why not turn carb heat off after applying full power and going around?

 

Rich

 

 

[JEM]

Some aircraft (eg A Cessna 152 I flew) have carby hot air not drawn through the intake filter so landing with carby heat on in such aircraft can result in dust in your carby.

 

 

[Downunder]

On final, you should be able to reach the runway with an engine failure should you not?

 

 

[Fishla]

This is kind of personal preference and depends on what your POH says and what your instructor says.

 

I pull carb heat before closing throttle. That is on downwind. But on a jabiru that does little to my available power. There is a drop but it is not as drastic as on other types I am told. I have no personal experience.

 

I leave carb heat on till touch down.

 

A go around is throttle push forward to full power and carb heat push forward to off.

 

It is fairly automatic now. I do remember once during training I went around. I applied full throttle and pulled the flaps up from full to half.

 

On the j120 the flaps are manual.

 

I was caught having to milk the flaps up halfway between indents.

 

So not having a third hand I asked my instructor to switch the heat off for me.

 

I was milking the flap because I felt the lack of power and lack of airspeed... It is not normal procedure. I was too quick on bringing the flap up and had missed the carb heat. It was a mistake.

 

So some say carb heat off on final.

 

I am almost idling or idling on final so I leave it on. Less power and less chance of storage or more power and more chance of stoppage?

 

The J120 POH leaves it up to the pilot to decide on the method. It only says turn heat off when going around but you are allowed "as required" for descent, whatever that means.

 

The J120 also allows ground operations with carb heat on so I can land with it on unlike the Cessna example.

 

I dont grab the flap lever before carb heat and throttle are forward anymore!

 

As to how quickly ice occurs? Don't know. But it probably takes too long to melt it when it occurs!

 

 

[facthunter]

I can assure you that having carb heat on for take off will cause significant power loss. Make Throttle forward/open/full and carb heat check COLD, an automatic action, ALWAYS is my suggestion. Sometimes people don't get the throttle fully open, (which doesn't help generally unless you have a very powerful plane where the power may have to be fed in judiciously to keep control). Nev

 

 

[Romeo Juliet Whiskey]

I can assure you that having carb heat on for take off will cause significant power loss. Make Throttle forward/open/full and carb heat check COLD, an automatic action, ALWAYS is my suggestion. Sometimes people don't get the throttle fully open, (which doesn't help generally unless you have a very powerful plane where the power may have to be fed in judiciously to keep control). Nev

Maybe it's just the jabiru I'm learning to fly in, but during runups there is only a tiny drop in rpm due to carb heat. Would this equate to significant power loss at full power?

 

 

[facthunter]

I've seen an LSA not get into the air on a touch and go. Aborted the TO at a late stage. Nev

 

 

[SSCBD]

Carb heat off mid to short final.

 

They should be no argument on this. You can get a large power loss and less response and if you are doing a missed approach or bounce and its usually with a xwind and need to get outta there you wont have time to stuff around with finding knobs you just want max power and "Rule One" fly the aircraft.

 

 

[SDQDI]

Maybe it's just the jabiru I'm learning to fly in, but during runups there is only a tiny drop in rpm due to carb heat. Would this equate to significant power loss at full power?

Some aircraft it will be more significant than others but it does make a difference. And obviously some strips will make the difference more noticeable, there is nothing like an approaching treeline and a lack of power to get your attention.

I learnt to fly in a beautiful J3 cub (is there a simpler more faultless plane around?), If the carb heat was left on and you had to go around being two up there was basically no climb at all so it made a huge difference.

 

 

[facthunter]

Without being too specific, I've always used about 200' which is about where you start giving it all to the landing phase. You are in the slot for the landing, mentally and with no large changes to anything like attitude the plane will arrive over the place you intend it to land on.. IF the throttle is opened for a missed approach I still confirm Carb heat cold. It's a critical manoeuver sometimes depending on circumstances, but you need FULL power most times. Nev

 

 

[Yenn]

If you turn it off too soon you may not be able to go around, you can ice up in the last 200' in a C150 and probably many other types. I believe keep it on until the landing is guaranteed, then you can turn it off. I found the Cessnas very prone to carby ice and have never had it in my RV or the Corby Starlet.

 

 

[facthunter]

A fairly long approach with no power on will not keep anything hot. Heat usually comes from a muff on the silencer, but evaporating fuel is one of the causes, of cooling in the carburetter,(the other is adiabatic expansion of gas, so more when throttle closed or nearly so). Apply FULL carb heat before reducing power and don't make long approaches when icing conditions exist. I've never had a carb icing event in a carb equipped Cessna. so far. Nev

 

 

[Roscoe]

Without being too specific, I've always used about 200' which is about where you start giving it all to the landing phase. You are in the slot for the landing, mentally and with no large changes to anything like attitude the plane will arrive over the place you intend it to land on.. IF the throttle is opened for a missed approach I still confirm Carb heat cold. It's a critical manoeuver sometimes depending on circumstances, but you need FULL power most times. Nev

I agree. That sums it up.

 

 

[mkennard]

Maybe it's just the jabiru I'm learning to fly in, but during runups there is only a tiny drop in rpm due to carb heat. Would this equate to significant power loss at full power?

I fly the j230 and doing an emergency landing with an instructor for a biannual I missed turning off the carb heat, I took off but the climb rate wasn't good and I caught it quickly. No significant danger but full power is different than run up power.

 

 

[kaz3g]

Without being too specific, I've always used about 200' which is about where you start giving it all to the landing phase. You are in the slot for the landing, mentally and with no large changes to anything like attitude the plane will arrive over the place you intend it to land on.. IF the throttle is opened for a missed approach I still confirm Carb heat cold. It's a critical manoeuver sometimes depending on circumstances, but you need FULL power most times. Nev

And if you regularly land on other than bitumen there is the ever-present threat of the engine ingesting foreign bodies including dust while the air filter is by-passed.

 

The late Terry Otway tested me for my Pilot Certificate and his short final check was "RFC" (Royal Flying Corps)

 

Runway clear

 

Flaps set

 

Carby heat OFF.

 

Kaz

 

 

[pmccarthy]

I was taught carb heat cold,as part of downwind checks. Anyone ebver had ice build up in the base final phase?

 

 

[SSCBD]

I was taught carb heat cold,as part of downwind checks. Anyone ebver had ice build up in the base final phase?

You were taught "wrong" sorry to say.

As stated

 

Carb heat off mid to short final.

 

They should be no argument on this.

 

 

[poteroo]

The late Terry Otway tested me for my Pilot Certificate and his short final check was "RFC" (Royal Flying Corps)Runway clear

 

Flaps set

 

Carby heat OFF.

If you do this at 200-300 ft agl, then add in 'WIND' A short final 'windcheck & runway clear' is good insurance

 

happy days,

 

 

[Toestub]

For what it's worth, I was taught to pull carny heat on as I drop revs to turn base, then turn off carby heat as I cross the fence on final. So far so good, did forget to turn off once on a touch and go and after the initial WTH I realised my mistake and rectified it and all was good on climb out.

 

 

[zodiacpilot]

Encountered carb ice twice, base & final at YSWH during flight from YWTO in the Monoplane, ch fixed it.

 

Then fan stopped at touchdown, 30 dg moderate humidity, should have left it on.

 

 

[facthunter]

Do what YOUR plane needs. IF you are in conditions where you suspect or have had carb icing Carb heat should be applied with quite a bit of power on for maximum effect, so do it with power on before reducing power for final. With a long power off approach there is a possibility it will not be effective so do what is necessary. Ie shorter approach with some power on. You only need the carb heat off if you want full power for a go round, so leave it on IF YOU NEED it, and if you have to go around you will have the power available and you check it is "COLD" at the same time as you check throttle full open. I advocate ANY time you do a go round CHECK FULL power applied and carb heat COLD. Make it an automatic reaction to check it. Nev

 

 

[Bleve97]

Our pre-landing check in the J160 includes carby heat on, then at ~200-300' AGL on final, carby heat off.

 

 

[kaz3g]

The little Continentals are quite prone to carby ice and it's important to also check pre takeoff to ensure the engine develops full power when pointing the aircraft down the runway.

 

And remember, if the engine stops due ice in the carby throat it is most unlikely to start again before a landing becomes mandatory.

 

A friend had his engine stop from ice just far enough out to negate any chance of getting back to the runway. He landed landed his Luscomb mon the CFIs grass strip which was closer instead.

 

Kaz

 

 

[kaz3g]

The following is from Bob Tait's blog:

 

Impact ice is really just an example of normal airframe ice that has formed over the air intake to the induction system. It requires sub-zero temperatures and the presence of supercooled water droplets. The application of carburettor heat will do nothing to remedy impact ice. If the aircraft is not equipped with alternate induction system air, the only other option is to descend below the freezing level. Impact ice is not at all likely for a VFR aircraft in Australian latitudes.

 

Throttle ice refers to the additional adiabatic cooling caused when the throttle is partly or completely closed. For example, in a glide passing through 5000 feet, the pressure upstream of the throttle is about 25" while the pressure immediately downstream of the closed throttle is about 10". This sudden pressure drop is accompanied by a significant drop in temperature in accordance with the gas laws.

 

 

 

The evaporation of fuel in the vicinity of the throttle adds an additional cooling effect due to the absorption of latent heat during the process of evaporation. This is sometimes called refrigeration ice - not a very appropriate name actually.

 

 

 

By the way, I once had a complete engine failure just after lift off in a Cessna Cardinal. In this case the problem wasn't ice, it was a collapse of the scat hose that carried induction air to the carburettor. When I applied carburettor heat, power was restored simply because the carburettor heat was an alternate source of air to the carburettor. Just goes to show that the application of carburettor heat after a power loss is always a good option - even if the problem is not ice.

 

 

 

Bob

 

 

Note that many aero engines, like Continentals and Lycomings, do have alternate air and application may keep the engine running if there is impact icing only. But of course we will not be flying VFR in conditions conducive to impact icing, anyway.

 

Kaz

 

 

[facthunter]

You are unlikely to get that form of icing, in our normal operations. If it covers the windscreen, it would also do the same to the forward facing intake/air cleaner, so you have a good warning. It's opaque not clear ice. Once the OAT is above freezing any that's formed will melt off. (Faster at higher temps). IF it's formed from super cooled water drops it can be quite rapid and also destroy lift on the wing so your stall speed will be elevated. Fly faster and get into warmer air.

 

The original set up on the small Continentals has a very effective heat source. (They meet a standard) and IF operated in accordance with the manual will keep ice out of the carb. unless you are descending with no power on, because the heat is from a muff on the exhaust, which cools when the engine is not delivering significant power. APPLY carb heat before reducing power for best effect. If it splutters and clears you HAD some ice but keep it on for a while to be sure. Nev