Lessons of Carby Ice ignored by instructors

[A37575]

Chatted to student undergoing C150 dual instruction at a flying school based in Rockhampton. He was told by his instructors there was no requirement to use carb heat before landing as OAT's are always too hot to permit carb icing to occur. Yet my understanding from reading Flight Safety Australia advice is that carb heat can occur at any temperature and therefore it should be set to carb heat control on until after landing. Most flying schools teach carb heat off on final but the Cessna 152/172 POH states carb heat on until the after landing check.

[andrew495]

I guess if you reckon its warm enough outside you could get by without it most of the time, but i'd rather have the assurance that comes with the heat on than risk having carby icing at low altitude in one of the most critical stages of flight. Its not as if it is much effort to put the heat on, and you'd certainly regret it if you did get icing. I was told to turn it off at 300'AGL, but you can't go too far wrong following the POH, so i would do what it says.

[404 Titan]

A37575

For those that are teaching student pilots that Carb Ice isn’t a problem in the tropics need to be re-educated. I’ve experience carb ice on at least three occasions, all in the tropics. Two were in the circuit at Cairns in a C150/152, one involving an off field landing and the other happened on climb out. The third happened in PNG in a C182. It occurred in the cruise and resulted in a dead stick landing at a place called Kikori.

[mingalababya]

Originally Posted by A37575

Most flying schools teach carb heat off on final but the Cessna 152/172 POH states carb heat on until the after landing check.

Yep, I was taught to turn carb heat off on final, but never told why. I assumed it's in preparation for a go around if required.

[scrambler]

I was taught Carb Heat off on final also, it was because unfiltered air and a dirt airstrip dont mix too well.

I also find it amazing the amount of pilots who don't understand the symptoms of Carby Ice.

[mingalababya]

Originally Posted by A37575

He was told by his instructors there was no requirement to use carb heat before landing as OAT's are always too hot to permit carb icing to occur.

If I can remember correctly from my BAK all those years ago, carby ice forms as a result of cooling from the Venturi effect. It has little to do with the OAT. I would have thought that carb ice formation is more prone in the tropics as well due to the higher humidity there?

[Avid Aviator]

Carb Icing Conditions

There's a great chart showing at what temps and relative humidities carb ice can occur - published in the CASA VFR Flight Guide, amongst others.
Anyone who's silly enough to suggest it can't happen in "the tropics" needs to pull this chart out and have a read before descent/approach. Alternatively, forming the habit of Carb Heat ON with power reduction, then OFF on final (or with power increase) means you won't ever have to worry about it....

[Dookie on Drums]

Originally Posted by scrambler

I was taught Carb Heat off on final also, it was because unfiltered air and a dirt airstrip dont mix too well.
I also find it amazing the amount of pilots who don't understand the symptoms of Carby Ice.

...and more importantly should you have to go around you would have full power available. Sure you could turn it off on the go around but it is one less thing to think about if you do it on final.

[HotDog]

Carb icing can occur at temps as high as +25 oC, especially in high humidity. The biggest risk is when temp and dew point are close to +20oC. I speak from personal experience flying a lighty in the tropics.

[Sunfish]

And furthermore, for some unknown reason, the C150 is more prone to carb icing then anything else I've flown, which is not a lot.

[Neil Taylor]

I teach that full carby heat to be used when there is any of the following three conditions:

1. Low air temperature < 20 deg
2. high humidity IE > 50%
3. Visible moisture - fog rain etc

I'm constantly surprised by the number of pilots who come through and don't use carby heat on approach on days when it's obviously required and the carby temp guage is in the yellow.

[multi_engined]

I was taught to engage carb heat in the downwind checks - bumpfisCh

then to disengage at 300' in the event a go around is required.

[magnum pi]

Learning to fly in the "Land of the Long Black Cloud" sometime last century,was taught to use C/H during run-ups,then on lining up for take-off(just a quick check).As for landing,was showed 2 ways....Aero club way,C/H on power back etc on D/W,C/H off on short final.Then by a well known av identity....much the same,but leaving it on till landed,making sure you have power all the way to the ground.If go-around needed,full pwr then C/H off......Then again theres nothing like using your BRAIN & using what suits your situation . Had ice on the ground early one morning in a 172(not visable),pulled heat on @ 1000rpm & got 500rpm increase!. PI

[scrambler]

And now are coming back the memories of flying the 182. From the POH (and a bit of memory) "Apply Carb Heat immediately prior to take off to clear any ice". The old 182 liked to ice up a bit.

That helped change my habit from "Carb heat during run ups to check it is working" to "Carb heat prior to take off, in case of ice"

PRE TAKE OFF -Monitor rpm whilst applying carby heat, if you get a slight drop followed by a raise in RPM you have ice, leave heat on until RPM stabilizes.

I know of someone who managed to stall an engine during ground running due to carb ice.