Use of carb heat

[RTN11]

We're having a bit of an argument at my school on standardising the use of carb heat on the final approach.

The other 2 instructors are teaching to apply carb heat when starting the approach on base, then on short finals at about 2-300' to put it back to cold so you have full power in the event of a go around or touch and go.

Surely if you are using carb heat there is some risk of carb icing, or you would not be using it at all. How does this risk go away in the final 2-300' of an approach? I have always been taught to leave it on, then if doing a touch and go move it to cold before applying full power, or if not leave it until the after landing checks. Since the store bought check lists state carb heat cold as an after landing check, this would seem to back me up.

I should probably say we operate PA-28s with lycoming engines.

[Cows getting bigger]

I teach carb heat to cold before applying full throttle. I know that is a play on words, but I think it is important to understand why carb heat needs to go to cold rather than prescribing a particular point when it should be set to cold.

[darn]

Agree with Cows Get Bigger.

Plus on final approach the student needs to be focussing on more important things than carb ht.

[what next]

Plus on final approach the student needs to be focussing on more important things than carb ht.

Indeed! With the same logic behind putting the carb heat back to cold at 200ft because of a possible go-around one could also retract flaps and gear at 200ft. Makes the go-around much more easy, believe me!

On the C152 we were taught (and still teach) to leave the carb heat on until after touch down and in case of a touch-and-go reset it with the thumb while the other fingers move the throttle forward. Unfortunatley, in a Piper this trick doesn't work. Therefore it goes like this (in our FTO): 1. Raise flaps, 2. retrim, 3. carb heat to cold, 4. apply power. If the runway is too short for that, we don't do touch-and-goes there.

Happy landings,
max

[Whopity]

How does this risk go away in the final 2-300' of an approach? Its simply a measure of time. Compare how long it takes to fly the approach from reducing power to being at 200-300 feet compared to the time from 200-300 feet to landing. The reason for selecting it off at that point is to ensure that you have full power for the go around.

In aircraft such as the PA28 you cannot operate the carb heat at the same time as applying power wheras in a Cessna type aircraft you can easily operate both controls at the same time. By turning the carb heat off at 200-300 feet there is little risk of ice forming in that short period of time and less risk of trying to fly away with less than full power. It also reduces the workload on a goaround.

[FlyingStone]

Carb heat should be (in my opinion of course) set into the cold position when you are able to glide to the runway in present configuration. This is usually at least 50', more likely 100' from the runway, so I think the workload isn't as high so the average student would get overloaded. Besides, on Cessnas where you actually need carb heat for every approach, carb heat lever is conveniently put right next to the throttle so it shouldn't be too hard to press the carb heat "button" fully in when reducing throttle to idle. On Pipers that's another story with lever placed far away, but it isn't required for normal approach.

I think that setting carb heat to cold on the ground during touch and goes isn't as damaging to the engine (I wouldn't want anything but clean, filtered air until venturi in the intake system) as is to the performance on climbout if left in hot position (mistakes happen, as we are all just human). For example, doing touch and go on short (yet long enough) runway with obstacles at the far end, I would always prefer to select carb heat to cold on short final then on the ground.

Oops, haven't noticed until now that you operate PA28s. Why do you even use carb heat during normal (powered) approaches, since Piper's (at least 28 and 38) intake system passes the oil sump on its way and is therefore naturally heated in the process?

[SNS3Guppy]

It really depends on what you're flying and why.

Just like pushing the propeller forward; some places teach it because they can't think outside the very small box in which they operate. Others do it for standardization. Others leave the prop back until the power is far enough retarded that they don't have to listen to the RPM wind up (my personal choice), and some don't push it up at all unless going around.

Carburetor heat isn't simply on because one is getting carburetor ice. The manufacturer doesn't have any way of knowing the conditions in which you are flying. You may be in conditions conducive to icing, or you may not.

Flying at idle power on a hot day with carburetor heat out can lead to fouled plugs, especially with a low idle and low heat. 100LL does that. That can lead to a very rough engine or engine failure on the go-around. I've experienced that. When one applies carb heat, one is enriching the mixture by virtue of decreasing air density with hotter induction air. I've removed spark plugs from airplanes doing nothing more than traffic pattern work,to find them completely glazed over...in large part due to pushing the mixture rich for the landing, and running too much carb heat. Especially on hot, high days.

What does your AFM/POH have to say on the subject? What does your company or training organization have to say? Are you teaching in an environment where you sacrifice personal technique for the sake of standardization? Are you required to match everyone else's procedure? The answers to these questions can determine your course...but bear in mind that if you do fall in step improper practices simply because everyone else is doing it, you'd best brush up on your forced landings, at some point.

Last year I worked with some individuals who were operating in a hot and high environment. The head training person was a former instructor at a respected college with a flight training program. He insisted that the mixture stay rich for ground operations, and go rich during the descend and landing. I was able to determine that his practice was leading to a lot of plug fouling and accounted for rough engines and rejected takeoffs. He wasn't familiar with clearing fouled plugs with engine and mixture operation; he wasn't familiar with proper mixture use, and he wasn't familiar with the requirement to re-adjust idle mixture any time an airplane is moved to a new base involving different elevations, temperatures, or conditions. He knew very little about his mixture.

You're asking about carb heat, I'm talking about mixture...because they're related and affect one another.

Likewise, if you're talking about a Cessna 172 or another airplane that uses a carburetor with an enrichment feature (making mixture richer at higher power settings), your use of mixture and carburetor heat can have a bearing on engine operation (or lack thereof) at high power settings (such as the go-around). If you're leaning for high density altitude (a good policy any time one has any density altitude of any significance), one needs to take the enrichment feature into account...most instructors don't seem to even be aware of it.

Discontinue carb heat early in the approach on a day highly conducive to carb ice, you may have a problem even before you reach the runway, or may have one upon arrival at the runway. Some engine/carburetor marriages are more conducive to carb ice than others.

In many light airplanes, I prefer to test carburetor heat for fifteen seconds on the downwind, just prior to my initial power reduction abeam the numbers. At that point, assuming it isn't a red-letter carb-ice day, I'll shut off the carburetor heat, make the power reduction, and carry power throughout the approach and landing.

I think many who cater to the carb-heat necessity also cater to the idle-descent school of thought...which is a poor practice in most light, piston-powered airplanes.

Bear in mind that the carburetor has a narrow range of temperature in which carb ice is likely. If one has a chance to operate an airplane with a carb air temperature gauge, one quickly learns that partial carb heat is generally in order, and only as necessary to keep the carburetor induction airflow in the proper, desired range. Without a carb temp indication, one is spitting in the wind and taking a wild guess.

Do you need it, or don't you? It's not the same on two different days, and not necessarily the same between two different airplanes.

[Cows getting bigger]

Compare how long it takes to fly the approach from reducing power to being at 200-300 feet compared to the time from 200-300 feet to landing. The reason for selecting it off at that point is to ensure that you have full power for the go around.

Noooooooo. What about the go around at 301ft? Will the inexperienced pilot put carb heat to cold or will he forget because he hasn't got to his 300ft check point? As someone has already said, the 152 lends itself to a nice double action with the thumb as you advance the throttle. Unfortunately, Mr Piper likes his throttle quadrant. :)

PS. I agree with everything SNSGuppy says.

[heading 125]

Slightly off topic - what do you teach for normal descent. I usually say any less than 1900 rpm on a warrier you apply carb heat. Carb heat off 100 feet before leveling off. Any comments

[mrmum]

I've got to agree with CGB, darn and what next. Essentially you should follow the procedures in the POH for the aircraft you are operating.

Here's an extract from a Cessna 152 POH, (my bold & red);


BEFORE LANDING
1. Seats, Belts, Harnesses -- ADJUST and LOCK.
2. Mixture -- RICH.
3. Carburetor Heat -- ON (apply full heat before closing throttle).

NORMAL LANDING
1. Airspeed -- 60-70 KIAS (flaps UP).
2. Wing Flaps -- AS DESIRED (below 85 KIAS).
3. Airspeed -- 55-65 KIAS (flaps DOWN).
4. Touchdown -- MAIN WHEELS FIRST.
5. Landing Roll -- LOWER NOSE WHEEL GENTLY.
6. Braking -- MINIMUM REQUIRED.

BALKED LANDING
1. Throttle -- FULL OPEN.
2. Carburetor Heat -- COLD.
3. Wing Flaps -- RETRACT to 201.
4. Airspeed -- 55 KIAS.
5. Wing Flaps -- RETRACT (slowly).

AFTER LANDING
1. Wing Flaps -- UP.
2. Carburetor Heat -- COLD.


If you choose to do anything different to this, like selecting carb. heat cold at 300' on the wrong day, trying to do a T&G, then ending up parked in a field off the end of the runway with carb. icing, you'll have a lot of explaining to do to the insurance company.:=

[FlyingStone]

What about the go around at 301ft? Will the inexperienced pilot put carb heat to cold or will he forget because he hasn't got to his 300ft check point?

At most airfields you are above the obstacles at 300' AGL, so the reduced performance doesn't affect you as much.

Heading 125: Normal descents should keep the engine RPM in the green or approximately above 2000 rpm, so the probability of carb icing is lowered significantly. You also have to take the enrichment of air-fuel mixture into effect, which would only additionally cool the engine in descent - so descending from let's say 6000 ft with carb heat set to hot and mixture rich (since most people do full rich except on cruise - or sadly, even there because of "the evil red knob") wouldn't do any good for the engine. Besides, if you use normal rates of descent for non-pressurized aircraft, you shouldn't even need to reduce the power below normal range while keeping airspeed in the green arc.

[CanAmdelta1]

Teach the student per the POH and require they do it precisely that way or dont sign them off. Then when the "ship hits the sand" they will perform as POH dictates.
Keep in mind on go arounds, most of the real ones seem to happen way less than 200' AGL.
On PFLs, carb heat every 500' drop in a 152 no matter the environment.
On 152, late d/w leg carb heat on and 1500 rpm, wait until air speed drops into the WHITE so we will still have flaps on the wings when we land.
If a moose runs on the R/w in front of you when you're 25' AGL please dont do the flap carb heat throttle, do the throttle carb heat flap thingy ok?

[Charlie Foxtrot India]

PA28 POH in Section 4 "Approach and landing" clearly states "Carburetor heat should not be applied unless there is an indication of carburetor icing, since the use of carburetor heat casues a reduction in power which may be critical in case of a go-around. Full throttle operation with carburetor heat applied can cause detonation."

To comply with this we apply carby heat on downwind and make sure there is no icing then leave it cold on the approach.

[Whopity]

To comply with this we apply carby heat on downwind and make sure there is no icing then leave it cold on the approach.Agreed however; on a Glide approach you do put the Carb Heat to Hot and in all my experience of teaching on the PA28 you select it back to Cold at about 300 feet so that it is not forgotten for the low go around. If you go around at 301 feet and forget, it really doesn't matter! I seem to recall this was even in a CAA approved expanded checklist for CPL skill tests.

[BillieBob]

In all my time instructing on the PA28, I have neither taught nor found it necessary to apply carb heat on a powered approach. As CFI points out, the PA28 POH specifically states that the carb heat should not be applied unless there is an indication of carb icing and I seem to recall that the Lycoming manual for the O-320 included a similar caveat. Certainly, the (CAA approved) checklist that I have in front of me makes no mention of carb heat in the circuit. Clearly, there is a requirement for carb heat in the case of the glide approach but, whether conducting a go-around or a touch and go from such an approach, it is difficult to imagine a situation so dire that there would not be time to select it to cold before applying power.

Since the original question related specifically to the PA28, the different requirements of the C152, or any other aircraft, are not relevant. Any aircraft should be operated in accordance with the relevant manufacturer's handbook rather than opinion, habit or urban myth. Insurance companies just love to find reasons not to pay out.

[Genghis the Engineer]

I wonder to what extent there is a wider issue here, of which sometimes incorrect use of carb heat is a symptom.

Older C150/C152/C172 aircraft, carb heat is a very good idea on approach. However, most PA28s it's specifically not required - the POHs are very clear on that point.

Similarly, sideslipping with full flap in any PA28 is a good way of losing excess height if you make your approach too high. Do that in a C172 and there's a reasonable risk of undemanded motion - which is precisely why it's recommended against in the POH (which again usually gets treated as a prohibition very often) .


Yet, I've flown with instructors who insist upon carb heat on finals in a warrior, and other instructors say I shouldn't sideslip the same type if I'm high on finals.


In my opinion, there are too many instructors who in the search for standardisation look to teach single "one size fits all" techniques that will map to any type. Again, in my opinion, this is just plain wrong - the right way to operate any particular aeroplane is individual to that aeroplane; by default as given in the POH, and differently only with careful and deliberate thought.

G

[Cows getting bigger]

There lies another problem, Genghis. A large number of club hacks either don't have a POH or it is locked in the CFI's office. Shocking behaviour but reality. I have worked at a number of clubs and it is worrying to find that the vast majority of students don't even know what a POH/AFM is. :{

[Whopity]

Only a few years ago the UK CAA held a second copy of the Flight Manual (when it formed part of the C of A) for every aircraft certified in the UK. A POH was for a Permit Aircraft under UK rules. Then along came EASA and they were all thrown in the bin!

[SNS3Guppy]

There lies another problem, Genghis. A large number of club hacks either don't have a POH or it is locked in the CFI's office. Shocking behaviour but reality. I have worked at a number of clubs and it is worrying to find that the vast majority of students don't even know what a POH/AFM is.

Any instructor that doesn't insist his or her student own a copy of the AFM/POH, isn't worth their weight in wet burlap.

How can an instructor possibly let a student go who can't work the performance charts in the airplane, and who doesn't know the systems and procedures in the airplane?

Very, very unprofessional. Forget whether the government or the flying club requires the AFM to be in the airplane. An instructor who doesn't insist on the student knowing the flight manual intimately, isn't worth much.

[Genghis the Engineer]

SNS - I agree, although sadly that does condemn a majority of FIs !

G

[SNS3Guppy]

How can that possibly be? I've heard from numerous pilots on this site that they aren't taught the use of carburetor heat or mixture control while learning to fly in the UK. I'm told here that most students never see an aircraft handbook.

In the US, an airplane isn't considered airworthy without an aircraft flight manual, issued to that particular serial number airplane. I've never heard of a flight training program that doesn't require a student to be thoroughly familiar with the aircraft operating manual.

Surely this is a joke?

Are students taught anything save "pull back to make the houses smaller, pull back more to make them bigger again?"

[Cows getting bigger]

SNS I completely agree and the availability of POH/AFM is also a legal requirement in EASA Land. Student owned copies of such documents are frowned upon as there is no document control over supplements etc. Nevertheless, the harsh reality is that these books sometimes don't exist (or at least pilots don't have direct access to them because the Head of Training/CFI has squirrelled them away in his office). As you imply, there is no point in getting a student a POH/AFM that isn't directly linked to a specific aircraft (ie one that applies to that aircraft registration). Of course, the engineering regime should capture these deficiencies but if the company that owns the aircraft also maintains it and has a 'cosy' relationship with the flying club then things can easily drift.

The 'employment' environment is such that if an instructor refuses to fly because of the lack of such documents, he/she may well be shown the door whilst passing the new instructor skipping-in through the same door.

The problem lies with our Registered Training Facility (RTF) process whereby the organisation is not subject to any significant regulatory audit as far as PPL training is concerned; about the only thing the CAA worry about is the integrity of the theoretical exam data. Schools which have FTO status (required for pretty much anything other than PPL training), are far better regulated and have a grip of their documentation etc.

PS. Don't even get me started about fuel planning. How about "Just fill it up and that will do"? :ugh:

[Genghis the Engineer]

In the UK and Ireland the POH is routinely locked away to make sure that the pilots don't mess them up, whilst in the USA the POH is kept in the aeroplane where virtually nobody ever gets the chance to read it. Either way, POHs are regularly kept well out of the way of the people who should actually read them.

Good generic operators manuals exist of-course, the best ones coming from the manufacturers themselves. Or, whilst it may be legally wrong, in reality it's generally fine to photocopy the official POH, stamp "uncontrolled copy" and give that to pilots who fly the aeroplanes.

The line that pilots should only ever use the absolutely official manual is of-course rubbish. Aircraft performance and mod states do not generally change year-on-year, and generic POHs such as AFEs don't actually list emergency drills very often: this is a really major deficiency. So, a photocopy done some time in the last 5 years is almost always fine.

I've nowadays got experienced enough and ugly enough to simply refuse to fly a new aeroplane until I've had a chance to sit down for an hour or more with the POH, and unless it's a type I know very well, that's exactly what I do. However, I've probably got 10 times the hours of the average club pilot and rather more than many club instructors - who between them don't have this realisation that there's a problem, nor the bloodymindedness to insist on it, which I think comes with age.

When I had maybe a quarter of my current flying experience I didn't do this on a particular occasion and broke an aeroplane badly, almost certainly as a result of not having read and used the CORRECT operating speeds for that particular flying machine - rather than the local "we do it this way" speeds. I've certainly not broken an aeroplane since, and I hope that the experience of that date is a major part of the reason for my more recent obstinacy.

G

[SNS3Guppy]

In the UK and Ireland the POH is routinely locked away to make sure that the pilots don't mess them up, whilst in the USA the POH is kept in the aeroplane where virtually nobody ever gets the chance to read it. Either way, POHs are regularly kept well out of the way of the people who should actually read them.

There's a big difference between requiring that the flight manual be available to the pilot at all times, and locking one away. In the US, knowledge of the aircraft flight manual is a legal requirement on which the applicant is tested. The student must know this as a student pilot, as a recreational pilot, as a sport pilot, and as a private pilot. Knowledge of the aircraft flight manual and relevant documents, as well as systems is further tested at the commercial and ATP levels.

Part of the private pilot practical test involves testing the applicant on his or her use of the pilot handbook to determine performance, weight and balance (separate, but generally contained in the POH), and to discuss systems knowledge, location of material, limitations, systems, etc.

In any event, the aircraft flight manual from the airplane itself not withstanding, every pilot should have a copy of the flight manual. I've arranged to own one for every aircraft I've every flown, for which a manual is produced. Whether it involved ordering one from the manufacturer, photocopying the one in the airplane, or otherwise buying my own, I always obtain the pilot operating handbook, aircraft flight manual, aircraft operating manual, or other flight documents for every aircraft I fly. I also always obtain the maintenance publications for the airplane, because these often provide more useful information about systems than the pilot documents.

I don't insist that students own the maintenance publications, but I always strongly recommend it. I also recommend that students take advantage of getting involved in a 100 hour inspection or other maintenance opportunities to see what makes the airplane tick.

If instructors aren't doing their utmost to ensure that the student is intimately familiar with the airplane and it's certification-required and legally-required documents, the instructor has failed the student. Whether or not the CAA, FAA, or anyone else checks up on this necessity, and whether or not the manual is available in the airplane, is irrelevant to the instructor's responsibility to the student.

As you imply, there is no point in getting a student a POH/AFM that isn't directly linked to a specific aircraft (ie one that applies to that aircraft registration).

I didn't imply that. Every student should have a copy of the AFM, whether it be the one in the airplane, or one from the manufacturer. There's no excuse to not have a copy, and to thoroughly know it.

The problem lies with our Registered Training Facility (RTF) process whereby the organisation is not subject to any significant regulatory audit as far as PPL training is concerned; about the only thing the CAA worry about is the integrity of the theoretical exam data.

This is no excuse. Simply because someone doesn't force the school or instructor to do his or her job properly has no bearing on whether it should be done.

If one finds a wallet or purse dropped on the pavement, one generally won't be forced to return it. Doing so, however, is proper and correct. Character is what one does when no one is looking. The description here speaks to a poor general character of the UK flight instructor, if indeed what's being presented is correct.

PS. Don't even get me started about fuel planning. How about "Just fill it up and that will do"?

A very poor character, indeed.

Whereas fuel exhaustion or mismanagement continues to be one of the leading causes for aircraft incidents, accidents, and fatalities, if failure to teach proper fuel management isn't criminal, it ought to be.

Fuel management isn't being taught. Students aren't being shown, let alone taught about the flight manual. It's not available in the aircraft. No carb heat education. No mixture education...one wonders if this isn't the tip of the iceberg.

[Genghis the Engineer]

Pretty much SNS, and I agree that the US system is a bit more robust than in the UK.

The only point that I'd disagree on is that British instructors are any poorer than American ones. The best of either country is superb, and in the US they're working within a slightly more robust system - but both countries have some very poor examples of the breed.

G

[hugh flung_dung]

SNS3Guppy: rest assured that the POH/AFM is available to students at most UK schools and (I hope that) most FIs encourage their studes to read them because the test requires a knowledge of aircraft systems (admittedly this isn't where the typical candidate shines!). The problem with some of the generic docs is that they have hopeless optimistic performance data and could lead a pilot astray (or into a hedge) if followed.
As G2G has implied, there are good and bad in all areas of enterprise and in all countries. Maybe the comments here are self-selected because the people that bother are the ones that care.

A different question: does anyone know the significance of a KFC150 AP passing its self test but not giving 6 beeps? The manual doesn't help.

HFD

[mykul10]

re:- each student having own copy of POH

POH forms part of CoA and is therefore unique to each aircraft, so the PoH belongs to the aircraft not an individual.

Yes, it is out of order for POH to be locked away. It must be available for flight planning and reference purposes.

Carb heat argument again brings out the question of generic (SEP) training vs type (small t) training.

By setting carb heat cold on final not only makes the go-around easier but also eliminates unfiltered air from the ground with all its dirt/dust etc going into the engine.

My final check is CRAP - carb heat cold, runway clear/correct, approach stable, cleared to land? if yes, then final flap and land in Cessnas and Warriors

[RTN11]

I agree that if no ice has been detected, and there is no risk of icing then carb heat should not be used, but in the UK pretty much every day in the summer there is a risk of light to serious icing with descent power as shown on the carb ice chart produced by the CAA AIC 145/1997. So even though no ice may be present before the descent is commenced, I would still put carb heat to hot on these days.

I always make sure my students are completely familiar with the systems on board, as well as weight and balance and performance before their first solo. A copy of the POH for each of our aircraft is kept alongside the FOB, which each student must read and sign upon joining as a member.

[POBJOY]

The truth is your location (inland or coastal) and (humidity levels) will be the main factor for all this and it is a bit late wishing you had applied c/heat after the engine falters.
With a very low power setting or the throttle closed there will be no detrimental effect to the engine with heat on and at least if you need to open up it will do so.
When i worked with an organisation using piston twins all the "engine issues" on approach or just before touchdown were always caused by not using "appropriate" carb heat for the conditions and usually with pilots from a jet or turbine background.
The touch and go situation also makes for an interesting incident (on a twin) when only one engine opens up on the "go around".
If you NEED to know your engine will repond after closing the throttle/throttles then have the heat ON it only takes a second to go to cold After they have responded.
Whether T&Go's are safe at certain "limited distance" airfields is another matter.
Remember the aircraft hand books are written for the country where the machines were made and "carb icing" is not such an issue as in Europe.

[DFC]

Ask yourself.

Which of the following do you want?

1. You keep carb heat on during the approach and if you have to go arround you apply full throttle and move the carb heat to cold. From this point on you have full power.

or

2. You keep carb heat off during the approach and when you have to go arround you apply full throttle and find that due to the ice build-up you don't get full power. Are you going to apply carb hear now and further reduce the power available?

The only way to guarantee you will have full power available for a go-arround is to make sure that there is no ice present. Please remember or review how ice builds up near the butterfly when at low power settings.

I am all for following the recomendations in the POH / Flight Manual. In the UK and most of Europe if you don't have heat applied then there will be some ice build-up. Therefore it is safe to say that on every approach you will have an ice build-up unless you have heat applied therefore in 99.9% of cases you will comply with the POH by having heat applied.

If you ever fly with an instructor / examiner and make an approach with the carb heat cold I expect that they will simply ask "Is there any carb ice?" If you can 100% say "No there isn't" then all is fine. However, I would love to know how you can say that is true.

Everyone should read and learn the POH/Flight Manual. They should also read and learn what is in the Engine Manual - and if you complain that few seem to read the Flight Manual then even less read the engine manual.

I recomend that everyone go to the Lycoming website and take the time to read what they have to say about carburettor icing. It's their engine after all!!!

[mavisbacon]

easy to push carb heat to cold and full power at the same time on the 152, bit tricky on other types and hence carb heat to cold at 300' taught.;)

[RTN11]

Having read Lycoming Service Instruction No. 1148C, dated October 12 2007

Landing Approach – In making a landing approach, the carburetor heat is generally in the “Full Cold” position. However, if icing conditions are suspected, apply “Full Heat”. In the case that full power needs to be applied under these conditions, as for an aborted landing, return the carburetor heat to “Full Cold” after full power application.

Would suggest to me that in the UK, where icing conditions are almost certainly suspected, to leave the carb heat on all the way to the ground, and only select to cold after applying full power for a go around.

http://www.lycoming.com/support/publications/service-instructions/pdfs/SI1148C.pdf

[Cows getting bigger]

RTN11, that will never catch on. Operating in accordance with the manual when you can be far better advised with old wives' tales and opinion given on pprune. :E

[A and C]

Quote Oops, haven't noticed until now that you operate PA28s. Why do you even use carb heat during normal (powered) approaches, since Piper's (at least 28 and 38) intake system passes the oil sump on its way and is therefore naturally heated in the process?

A very interesting veiw of the location of carb ice, I would think that the reason carb ice is called carb ice is because it forms in the carb. The carb is bolted to the bottom of the sump and the ice forms before the mixture enters the area of the inlet that is heated by the hot oil in the sump.

I find the most interesting part of carb icing it that the likelyhood of ice forming can be quite different between aircraft types fitted with the same engine/carb leaving me with the opinion that the intake system has a large part to play in the formation of ice in the carb.

[tonker]

Absolutely agree with mykul10. CRAP checks at 300' give the best of both worlds, be it the go around with more power and no unfiltered air exposed to the engine in the enviroment where the little beasties potter around in.

[A and C]

This unfilterd air thing is a bit of a red herring unless you are flying in a very dusty enviroment, the route that the air takes when going from inside the cowling through the heat exchanger and into the carb is very likely to filter out most of the rubbish.

[DFC]

This unfilterd air thing is a bit of a red herring unless you are flying in a very dusty enviroment, the route that the air takes when going from inside the cowling through the heat exchanger and into the carb is very likely to filter out most of the rubbish.


Agree overall. However, have you ever compared a prop that lived in the 1000ft to 8000ft band to one that spent it's life above 10,000ft. Lots more errosion at low level due to the dirty air.

Take a 2000hr engine. How many hours will it have spent eating unfiltered air (carb heat on) - not very much (even if it is a training aircraft). and I have not experienced any difference in the state of the 2000hr engine on a Cessna - Carb heat on to touchdown when compared to a similar age engine on a piper - carb heat off.

Don't do anything that will cause the engine to stop unless you want to be a glider............don't let ice build in the carb.

[A and C]

Three of my aircraft have the Chalenger air filter fitted (aviation approved K & N automotive filters) these are cleaned at 100 hours, most of what comes out in the wash is grass & insects along with small amounts of fine dust. The dust is more noticable in the summer.

I also look after a number of Extra 300 aircraft, these have no filter as such just a "rock screen" in front of the injector body to keep out the "bugs & Grass". If filtered air was a big issue one would expect these engines to show evidence of damage by abrasive substances. Most of these engines don't make TBO but the usual faiure mode is crankcase fretting as a result of the extra crankshaft loading due to aerobatic flight, not anything to do with air filtration.

It will probably not astound you all that despite the fact that my Chalenger airfilter equiped aircraft were flying throughout the volcanic ash crisis no unusual debris were found in the air filters during cleaning.

[boofhead]

I don't see how putting the carb heat to cold at 300 feet helps to remember it. Many students are way too busy at 300 feet and will easily forget. If they are accustomed to just pushing the throttle to full power on a goaround or touch and go, and they usually have cold already selected, what will happen if they forgot to do it at 300 feet? They would net even be accustomed to re-checking it and I can see a loss of power causing an accident.
Better to always push in the carb heat with the throttle, or at least confirm that you have full power by eyeballing the heat control early after pushing the throttle up. It also gets them accustomed to more complex engines, with prop and cowl flaps, both of which should be checked every time the throttles are pushed forward. Make the carb heat part of the operating procedures, not a memory item. Less likely to be forgotten, and also a reminder to check it when it really counts.
I have seen students leave the heat on during a go around or touch and go, or pull the mixture instead of throttle when turning base, or set full throttle with the props at cruise, leave the cowl flaps closed during a go around, not close the cowl flaps on the "failed" engine, etc etc etc and making the controls part of a checklist procedure instead of an operating procedure does not work when it counts. Too easy to be distracted.
In real cold conditions a C150 type needs carb heat on the ground and on takeoff and landing or else the engine simply does not run. You will lose the engine on go around if the heat is not applied, and will lose it on touch and go as well. The POH should be followed, and it requires full heat for approach until after landing (and on normal surfaces I leave it until shut down on the ramp). On takeoff or go around, set full throttle first, wait a second to let the warm air do its job clearing the carb of any ice before pushing the carb heat back to cold.
The PA28 should be left in cold unless icing is suspected.

[tunalic2]

The debate goes on!
one size fits all or 'know your aircraft'

to answer the original post

I think you should agree to standardize so all instructors teach the same way at your particular school.
This results in less confusion for your customers.

T2

[Genghis the Engineer]

Same school and type, absolutely. Same school, all types, definitely not.

G

[pasir]

... Regarding application of Carb Heat - I seem to remember that how and when this was applied would often depend on who was the
instructor of the day. Later I was very fortunate to gradujte to
a Rheims 172J (fuel injection) that had the advantage of no longer having to continually bear in mind carb. heat. Thereafter whenever looking to changing an a/c I would never consider going back to any non f/inj. a/c. - along the lines that once many car drivers have driven with automatic gears then most would probably be reluctant going back to manual shift.

Apologies if this adds little to the debate

...

[CaptAirProx]

I agree with the likes of Genghis that we should make people more aware of the aircraft operation in question rather than teach a one size fits all. I do not buy the argument that states the manual for a PA28 says not to use carb heat - well it does, but read carefully as I think someone already here has elluded.

I do not have a copy infront of me BUT, when this was argued before on here and at my school I read several manauls again to check my understanding. It says something along the lines of carb heat is only used on approach when icing conditions exist. Well, as we have already discussed earlier, 99.9% of the time in the UK icing conditions do exist according to CAA safety sense leaflets and AIC's etc . . . oh now there is a point - how many students have heard of those or even read them . . !?!?!?!?! Let alone the aircraft manuals.

[SNS3Guppy]

Carburetor ice is a function of physics, not checklists.

You're faced with two issues when confronted with a checklist calling for carburetor ice. One is the utter lack of defense you'll have if you incur a power loss due to carburetor icing, if you didn't use the carburetor heat. Explain that to your insurance carrier when they seek litigation for damages to to aircraft, passengers, and property on the ground. The other issue is more personal to you; the actual operation of the airplane, your safety, and of course, your legal requirement as pilot in command to ensure the safe outcome of the flight.

First of all, why touch the control if you don't know how to use it, or what it's for? It's there to heat induction air. Why, and by how much?

Without a carburetor air temperature gauge, you have no idea how much heat you're putting into the induction air, let alone the temperature value of air passing through the carburetor venturi. That air must be within a certain range to prevent icing. Too high or too low, and you enter ranges that are either conducive to icing, or that are detrimental to engine operation (particularly at high power settings). Further, by unnecessarily using carburetor heat, you limit available engine power, and substantially alter your fuel-air mixture...which can lead to plug fouling and power loss in some cases. So...before you touch that control, do you have any clue what you're doing, or are you parroting what a low-time instructor told you to do, because that's what he or she was told to do? Worse, are you doing it because you read about it on the internet? Bad form.

What types of carburetor icing are there, and how do they differ? Did anybody ever discuss this with you before advising you when and where to apply carburetor heat?

Carburetor ice, or more accurately induction ice, tends to form in three ways. Two of them occur in the carburetor, and one of them doesn't (and can't be affected by carburetor heat). Induction ice at the air intake (typically around the air filter) occurs when flying in freezing conditions and visible moisture, and can't be removed by carburetor heat. It can only be prevented by not entering conditions that cause such icing.

Carburetor icing, inside the carburetor, however, is more insidious, and occurs on warm summer days well outside of visible moisture. It occurs in two ways; at or close to idle, and with an open throttle. Too often students are mislead to believe that carburetor icing is a product of operating at low power settings, when this is patently untrue.

Your carburetor has two fuel jets, or inlets, which provide fuel to air flowing through the carburetor, and give your engine life. One is an idle jet, which serves the carburetor only when the throttle plate is closed. The engine, acting as a heavy vacuum cleaner or suction machine, draws air through the air filter and carburetor. When the throttle plate is closed, this is the same as placing one's hand over the hose on a vacuum cleaner; the pressure in the hose drops, and the machine (engine) sucks away at your hand...or in this case, the closed throttle plate.

Some air gets past the throttle plate, and this happens at a point where a controlled leak is allowed...this is precisely where the idle jet is placed, and also where carb icing occurs at idle. Block that small controlled leak at idle, and one cuts off the airflow to the engine. Cut off the airflow and one cuts off the pressure drop in that same location that draws fuel into the airstream, and subsequently the engine quits from lack of airflow and lack of fuel. Opening the throttle makes this problem go away; the carburetor isn't choked off from icing...just the edge by the idle jet. Carburetor heat prevents this icing in the first place.

During a prolonged descent with idle power, the engine cools, and carburetor heat becomes less effective. Carburetor heat in most light piston powered airplanes is little more than a small door in a box ahead of the carburetor which is moved to allow air from inside the cowling to be drawn into the carburetor. This air is warmer than ambient air outside the cowling. How warm this air is largely depends on things such as the position of cowl flaps (where installed), the airspeed and airflow of the nacelle (how fast it's receiving cooling air, and how much), and the power setting of the engine. An engine operating at a high power setting is hotter than an engine at idle, and makes for hotter air inside the cowl. Closed cowl flaps make for hotter air than open ones, and so forth.

One must realize that in a small piston engine installation without a carburetor air temperature gauge, one is taking a shotgun approach to removing or preventing icing. One has no idea where in the carb temp range one is placing the carb air temp, when applying carburetor heat. It's what one might call a swag, or scientific wild-assed guess...hardly appropriate in the artistic science we call flying, but often all one has when attempting to control carburetor icing.

Most airplanes don't come with an ice detector, either, so one has no way of knowing if one has ice, or has removed ice, unless one understands the formation of icing, it's removal, and how to tell the difference by power response, vibration, and sound.

The other kind of carburetor icing occurs with an open throttle, which may be partial, or wide-open throttle (WOT); it can occur at high power settings in cruise or on takeoff...or on the go-around.

Both kinds of carburetor ice form as a result of a drop in pressure and temperature at the carburetor venturi, or by the calibrated leak at the idle jet with a closed throttle. Pilots are often mistakenly taught that carburetor icing only occurs at low power settings, when in fact a high power setting produces the greatest airflow and temperature drop, and can produce the fastest power loss. Think about it. This occurs at wide open throttle or partial throttle...such as a takeoff or go-around. Given some of the comments about the lack of training that's provided, I have to wonder how many have considered the possibility or likelihood of carb icing during those critical phases of flight.

Don't be lulled into thinking that the only times to apply carburetor heat are when one is approaching to land. Carburetor heat, like the mixture control, is there to be used. One does not need to rope one's self into a constraining and artificial mental limit of thinking that one cannot use it liberally as required. One can, and must. I've seen pilots land shaken and unsure about the engine failure they just experienced...when in fact they just lost power due to carburetor icing...and had absolutely no idea. I've seen them look astounded when a short time later we were able to start their airplane and run it normally...they were absolutely convinced that carburetor icing couldn't have happened to them...after all, they were at a high power setting on a hot day. Carburetor ice? Naw...can't be.

It is.

When one has been using carburetor heat during a prolonged descent and approach, and one pushes it in at the moment of go-around, one may suddenly develop carb ice, and get a rough engine. Or one may already have carburetor ice, shed some of it off the throttle plate as the throttle is advanced, and get a rough engine. Or one may see no response at all. Knowing which is which, and what to expect, may make the difference between abandoning the go-around and landing on the remaining runway, the re-application of carburetor heat, or even an unnecessary execution of a forced landing off-field.

If one has been using carburetor heat during the approach, especially without a mixture change, one may have significantly enriched the mixture. With 100LL fuel, which contrary to the name does contain a high concentration of tetraethyl lead, spark plug fouling is a distinct possibility. If one has flown a prolonged descent with carburetor heat and no leaning, one may push the power up and find a rough engine that can't be cleared with additional carburetor heat...because the spark plugs are fouled. I've seen student after student, and instructor after instructor, bring me an airplane repeatedly throughout a single day, with reports of a rough engine. Upon pulling lower spark plugs, I have found completely shorted spark plugs, glazed over with lead and carbon deposits, which must be chipped free using a pick, and the spark plug thoroughly cleaned before being returned to service. The problem wasn't the magneto gap, it wasn't the spark plug, and it wasn't a timing issue...it was a pilot issue and a failure to properly lean, and too much unnecessary use of carburetor heat.

Rather than teach rote use of the carb heat control, one should be teaching proper use, as well as the principles of it's application, and the principles of carburetor function. To fail to do so borders on criminal behavior, and is highly inappropriate.

[boofhead]

Excellent post, thank you.

A DC3 in Aus many years ago had carb icing in cruise on a nasty night. The crew applied full carb heat, disregarding the Carb Temp indicator. They continued on, with the engines both detonating badly due to the intake temperature (well over 40 degrees C) until both engines failed and they crashed, killing all on board.

Many years later, also in a DC3 I was flying over the Simpson desert on a search with an OAT of 45C. Both engines backfiring every 30 minutes or so. What I needed there was carburetor cooling!

[RTN11]

That really clears up a lot.

If only there were more engineers with the experience, knowledge, and time to help pilots better understand the engines that keep us aloft.

I have been guilty of teaching on the same fly by numbers routine that I was once taught, until I myself learned better. Befriending a few engineers myself has helped me right a few of my own shortcomings.

We're due to be getting a Cessna to go alongside our PA28s, so I just hope the other instructors welcome teaching different use of carb heat for different engines, or I will have a battle.

[aussiefan]

As a fairly new student I have been following this thread with interest. My usual instructor only uses heat in known icing conditions. If needed it goes on before turning crosswind and off at about 300ft. This is a C172 in Australia.
The other instructors have different versions.
The manual says to put it on on approach and take off before applying full power.

[FamousGrouse21]

I have flown exclusively in PA28s since my training days and was always taught to use full carb heat on approach and then switch it off at 300'. However, upon reading this thread I may try to leave it on as late as possible to avoid any chance of carb ice build up during the round out and landing run. Having read the entire thread I have to say the debate regarding use of carb heat seems endless!

Grouse

[Intercepted]

In the UK "known icing conditions" are most days of the year according to the graphs we have in the PPL ground school books (regardless of aircraft type), and therefore we are taught to do a FREDA check every 15 minutes, which includes turning the carb heat on for 15-30 seconds. Apart from this we are normally taught to always use carb heat in descent (normally 2000rpm or lower).

What's described above is probably the correct use of carb heat certain days of the year and/or in certain aircraft types, but for "safety" reasons we follow the procedures at every flight, or do we?

http://www.fly13.co.uk/Tug/Carb%20Ice/Carb%20Icing%20Chart.jpg

I'm going flying tomorrow, and yes, according to the graph it will be SERIOUS ICING - Any Power :ok:

[24Carrot]

If one has been using carburetor heat during the approach, especially without a mixture change, one may have significantly enriched the mixture. With 100LL fuel, which contrary to the name does contain a high concentration of tetraethyl lead, spark plug fouling is a distinct possibility. If one has flown a prolonged descent with carburetor heat and no leaning, one may push the power up and find a rough engine that can't be cleared with additional carburetor heat...because the spark plugs are fouled.I read this with some interest.

The R22 helicopter has a PA28-style 180hp Lycoming engine (though it's derated) and burns 100LL. I was taught (in the UK, so seldom hot or high) to use Full Rich mixture all the time, and always use full Carb Heat for descents. Unlike Fixed-Wing, every Rotary descent to land ends with something like a 'go-around' because you need nearly maximum power just to hover.

Landing an R22 requires serious attention to several details, but I have never been warned about this one. I am very low hours rotary, so I will ask next time I see my old instructor. Though if anyone here wants to chip in...?

[Cows getting bigger]

R22 vs. PA28 differences:

Derated engine
Different intake manifolds etc
Variable CH - have a gnatty little gauge to tell you the actual carb temp.
Gradual change of power - you don't 'yank' on the collective. Final approach is probably at about 15in MP with this being slowly increased to about 23/24in in the hover. All that takes quite a while as you decelerate from 50-60kts and about 300ft to the hover. I don't think this is anything like the fixed wing go-around scenario.

[Genghis the Engineer]

I have flown exclusively in PA28s since my training days and was always taught to use full carb heat on approach and then switch it off at 300'. However, upon reading this thread I may try to leave it on as late as possible to avoid any chance of carb ice build up during the round out and landing run. Having read the entire thread I have to say the debate regarding use of carb heat seems endless!

Grouse

Sorry to seem dense, but having read this thread, where it's explained that the PA28 manual specifically says you shouldn't use carb heat on approach unless there's evidence of icing, and that excessive use of carb heat can damage engines - you are planning to go even further away from the advice in the manual and use carb heat more?

Or did I miss something?

G

[FlyingStone]

However, upon reading this thread I may try to leave it on as late as possible to avoid any chance of carb ice build up during the round out and landing run.

Presuming you are making full stop landing: what difference does it make whether you have engine power available during round out and landing roll? Go-around in a PA28 when you have three wheels on the ground is pretty useless, since stopping distance (especially on grass strips) is much less than takeoff distance (with obstacle clearance of course, since you want to avoid for ex. traffic that has entered runway without clearance). Besides, I don't think carb ice would build up from 300' to flare if you have used full carb heat during approach - even in maximum carb icing conditions. All you will do by applying carb heat during the flare and landing roll is to expose the engine to all sorts of stuff that lies in the layer extending from the ground to few tens of feet above.

And as Genghis said - if manual says only to use it when there is evidence of icing and you do not have CAT gauge, I suggest you do as manual suggests.

[24Carrot]

CGB,
Gradual change of power - you don't 'yank' on the collective. Final approach is probably at about 15in MP with this being slowly increased to about 23/24in in the hover. All that takes quite a while as you decelerate from 50-60kts and about 300ft to the hover. I don't think this is anything like the fixed wing go-around scenario.I agree it is not a yank, but most of the power goes on in the last few seconds of the transition to hover, (as evidenced by the left foot suddenly needing to wake up).

15in MAP is typically set during downwind, so the profile is roughly 3 minutes of low power followed by a 3-5 second change up to 22-24in MAP, which sounds quite like the plug-fouling scenario mentioned previously. So I am a litle surprised I haven't heard of it happening.

Presumably icing is the bigger risk, so carb heat goes on, and the fouled-plug engine failure is the less likely of the two evils. Also, under 500' you don't have a spare hand to change the Carb Heat setting, so you must choose one setting for the whole descent.

[Capot]

We were taught 45 years ago to select carb heat (Austers) when reducing power for the final descent, and keep it there until the end of the landing roll or when applying power for a go-around or touch-and-go.

As someone said, in some aircraft you can deselect carb heat with the same hand that opens the throttle.

We did it the same in the club's Piper and Cessna aircraft, and I've done it since in every piston I have flown.

Works for me. I would imagine that reverting to cold air for the last 300' of a proper glide descent, on the wrong day, could pretty much guarantee a certain lack of response for a go-around. And knowing if it's a "wrong day" is quite difficult.

If you're going to drag a single-engine piston in under a high power setting then that might change things. But maybe you need to learn to fly properly, so that you can land on the airfield from any point of the circuit if it all goes quiet. At least that's what we were taught.

[Genghis the Engineer]

We were taught 45 years ago to select carb heat (Austers) when reducing power for the final descent, and keep it there until the end of the landing roll or when applying power for a go-around or touch-and-go.


Austers (and Chipmunks) I'd normally leave carb heat on pretty much all the time - a Gypsy Major thing.

G

[Capot]

Cirrus (Minor?), as it happens, but much the same propensities....

I did own a Gipsy Queen for a while....it wasn't just icing that stopped it; cloud had the same effect on occasions, it didn't like damp.

[24Carrot]

Also, under 500' you don't have a spare hand to change the Carb Heat setting, so you must choose one setting for the whole descent.
Of course you have a spare hand. The admonition to keep your hand on the throttle all the time can be taken just a little too literally. Be ready to more the throttle, power levers or thrust levers if you need to...but if you need to manipulate other engine controls, then do that. One may need to adjust mixture, adjust propellers, or adjust carburetor heat during the approach, including below 500'. I spent a lot of my career operating well under 500'...if I'd never taken my hand off the power levers, I'd have been awfully limited in the cockpit! To be clear, I was talking about an R22, because it has a Lycoming like the PA28.

The right hand is permanently occupied with the cyclic. Anywhere near the ground the left hand holds the collective, in order to lower it quickly if the engine fails.

Fixed wing, of course I agree, you usually do have one hand free. Most of the time, you have two hands free!

[Mickey Kaye]

Shouldn't the Carb Heat control been designed out of pistion aircraft by now?

The rotax powered microlights have managed to do it so why not the continental and lycoming fleet.

There can't be a month that goes by without an accident report related to carb icing.

[darkroomsource]

Follow the POH.
period.
You may think you know more than the manufacturer of your airplane about physics, weather, etc. etc., but I doubt you do, even if you have a PHD in physics and/or weather, the manufacturer probably had several people with PHD's involved with many decades of combined experience involved in the development of the POH.

Besides the notes about always doing it the exact same way, so that it's ingrained, there's the liability situation, and a level of comfort in knowing that if you're at X stage the controls will be at Y. If not, you know something is wrong. There's the fact that someday you may be flying in different conditions than you do at your home airport in the middle of summer when this student learned what to do with the controls. Additionally, having the carb heat on fully is a reduction of what, 50 RPM, but having had to use carb heat on a few occasions I can tell you that with the carb heat off, you lose much more than 50 RPM.

[Cows getting bigger]

24Carrot - The book says max carb heat below 18" MAP and the rest of the time sufficient carb heat to keep the CAT Gage (American spelling :ugh:) out of the yellow arc. if you're fortunate enough to fly the O-360 version (Beta II), you have the advantage of Carb Heat Assist.

It isn't pretty and definitely worth chatting with an instructor first, but it is possible to change the carb heat setting with a very quick removal of hand from collective. :eek:

[24Carrot]

It isn't pretty and definitely worth chatting with an instructor first, but it is possible to change the carb heat setting with a very quick removal of hand from collective.

Both points noted!

[gpugh]

Hi , just come upon this thread, in the case of the Chipmunk,mentioned some time ago, and in particular the section reference the carb heat control being wired into the hot position by the RAF at one point, my father, who was at that time the Naval Flying Grading Examiner with the flight of 12 Chipmunks belonging to the Royal Navy, was discussing this point with me only yesterday to the effect that he would not allow the Navy's Chipmunks to have the carb heat control wirelocked in hot in this way as he considered it dangerous to do so, firstly because of the reduction in power that it caused and also because it could also induce carb icing in some conditions when it would not have normally occured without any further way to get rid of it. He was asked by the Navy to write a paper on the subject which I think led to the RAF also de wiring their aircraft.
Gordon

[SNS3Guppy]

Follow the POH.
period.
You may think you know more than the manufacturer of your airplane about physics, weather, etc. etc., but I doubt you do, even if you have a PHD in physics and/or weather, the manufacturer probably had several people with PHD's involved with many decades of combined experience involved in the development of the POH.

Carburetor heat is a tool. Much like the throttle, much like the mixture, the manufacturer doesn't tell you precisely when to use it and when not to use it; use it as conditions dictate.

Advocating blind adherence to guidelines is to advocate ignorance, and is no way to teach, learn, or operate an aircraft.

Guidelines are there to start you down the path. Not to chain you to it.

THINK!

[DFC]

Follow the POH.
period.



Exactly. The POH in question clearly requires the use of carb heat on approach in the typical conditions that exist in the UK throughout 99% of the year.

The engine manual also has important information. How many read that?

It is a good idea to treat the use of carb heat described in the manual as a minimum and it is often prudent to use it more often. Just as the performance figures in the manual can be acheived some times but it is prudent to err on the safe side when deciding just how long the damp grass strip with a slope needs to be.

What is put in the POH is a result of a pilot writing what in their opinion needs to be done and then 10 Lawyers re-writing it to what they think will cause the least posibility of liability.

Has anyone here ever bothered to pose their scenario to the Type Certificate Holder and get a letter of no technical objection or other response?

The problem with private flying for the most part is that the operators (owners) never talk to the manufacturer / type certificate holder about technical issues and everything ends up in rumour / local practice / blind following of rules designed for a limited set of situations.

[SNS3Guppy]

One can be a slave to a checklist (which is not a "do-list"), or one can understand the rationale and the system, and apply it accordingly. One can foolishly extend the logic you suggest, and say that because the manual at any given time doesn't call for carburetor heat, then one should not apply it...a very dangerous view to take.

Carburetor heat is a tool available to the pilot. Use it accordingly.

[darkroomsource]

One can be a slave to a checklist (which is not a "do-list"), or one can understand the rationale and the system, and apply it accordingly. One can foolishly extend the logic you suggest, and say that because the manual at any given time doesn't call for carburetor heat, then one should not apply it...a very dangerous view to take. Carburetor heat is a tool available to the pilot. Use it accordingly. And one can fail one's checkride for not following the POH. And one can be sued because one did not follow the POH. I have never seen a POH that said to not use carb heat when you need it, I have seen where it said that it should be used even when you don't think it should under certain circumstances, and that's what we're talking about. Should you use carb heat just because the POH says to when approaching to land. YES, you should, someone, or more likely a BUNCH of someones with more degrees and experience combined than any of us come close to having, made a decision that it was SAFER to have the carb heat ON during desecent and approach thatn to have it off. So they put in the POH to have it ON for approach. If they wanted you to have it off when the outside temp was above X, they would have said so, if they wanted it off above X feet MSL, they would have said so. This, of course, only applies to engines and planes where the POH says to have it on. If the POH says to have it off, then by all means, it is safer to be off in that particular combination of airplane and engine. Again, if one decides that one is smarter than the engineers and lawyers, one can go ahead and do whatever one wants, but please don't do it with other peoples lives.

[SNS3Guppy]

Aviation history is replete with fatalities punctuated by simple omissions or inclusions. For example, the Cessna 206, 207, and 210 have a procedure for Fuel Flow Fluctuation which, if followed, can ensure an unrecoverable engine failure. The factory direction to apply fuel boost, switch tanks, and adjust mixture is nearly correct, but not quite so. Having experienced this same condition myself, in the mountains with an airplane full of passengers and cargo, I can tell you that systems knowledge goes a lot farther than blind adherence to incorrect procedure. In the case of that particular airplane, swapping tanks first makes all the difference in the world, regardless of how many doctorate-holders you think may have been involved in the construction of that fuel system.

The same goes for many aspects of aviation.

Many won't lean their engines below 3,000' because that's what they think they're being told in the POH. Many won't do it below 3,000 or 4,000' pressure altitude or indicated altitude, though in reality the intent or such language in an AFM or POH has to do with idiot-proofing the directions, and refers to density altitude...because the use of mixture is a function of air density!

Many will do a run-up on the ground and check carburetor heat briefly for a drop in RPM, but won't bother to check to see if they have actually been developing carburetor ice. I've seen pilots do their run-up satisfactorily, then proceed to the runway for takeoff and experience an engine failure from carburetor icing. Go figure. A better technique, one not specifically called-out by manufacturers, is to run the engine up on the runway for takeoff, do the carburetor check there at the last moment (ensuring that one not only has checked for function, but specifically for carburetor ice, and given the tool time to work)...as well as taking the time after carb heat is shut off to adjust mixture for takeoff power (not simply for the runup as many mistakenly do)...then proceed with the takeoff.

Engine manufacturers recommend post-flight runups, idle mixture checks, and so forth...it's a rare thing to find an instructor or pilot who has the slightest clue about these things, or who has actually read the engine manufacturer's pilot instructions or engine operation recommendations. Most stop short and read the POH or AFM, and many (as we've seen discussed here before) don't even do that. We've had assertions from a number of UK/European renters, pilots, and even instructors, that the aircraft flight manuals aren't available to the pilots who fly or rent the airplanes (a truly mind boggling conundrum...not making the pilot handbook available to the pilot).

Remember that the pilot handbook is the most distilled and dumbed-down version of all data available for the airplane. It does include important information, but it's also the most watered-down of all the documents regarding the airplane. There's a good reason for it, too.

[FlyingStone]

And one can fail one's checkride for not following the POH.

I bet you'll find a lot of examiners who will fail you for leaning the mixture on ground (remember: you are burning vales with leaning!!!!! :ugh::ugh:), leaning LOP, not decreasing the power after takeoff (on engines without 5 min full power limit), etc. You shouldn't blindly believe everything an instructor/examiner says, just because they have FI/FE rating... And of course, there was no accident in history of aviation where POH/AFM/QRH was wrong :ouch: You should always remember that POH is mainly written by lawyers trying to protect manufacturer from lawsuit, not pilots/engineers.

I have to agree with SNS3Guppy, many pilots just don't bother to study the aircraft thorougly (AFM, checklists, engine operation manual, etc.), they just follow the checklist and trust it like it's made by god. I believe the main reason for this are instructors, who - instead of passing the knowledge, which wasn't part of groundschool - just simplify procedures (full rich mixture is just one of many). This results in overall decreasing knowledge of aircraft systems which I believe it is vital for understanding the procedures described by checklists - if we eliminate understanding from aviation, we don't need pilots, there are plenty of monkeys on this world... But who to blame, in our lovely JAA/EASA world with our lovely ATPL exams, which don't check for actual knowledge or understanding of the subjects, but only require remembering hundreds of numbers by heart and many in today's generations just want to pass the exams, not study for them and actually understand what's going with aircraft and its systems...

[SNS3Guppy]

I bet you'll find a lot of examiners who will fail you for leaning the mixture on ground (remember: you are burning vales with leaning!!!!! ), leaning LOP, not decreasing the power after takeoff (on engines without 5 min full power limit), etc.

Whomever taught such ridiculous things?

Pilots really belief that leaning burns valves?

Pilots really believe that one shouldn't lean for takeoff, or lean on the ground? Have you only flown at sea level and on cold days? If so, perhaps one could be forgiven for not knowing this, but one's instructor can't be, for failing to teach properly.

Pilots really believe that one can't and shouldn't operate lean of peak?

Sadly, an examiner will fail one for doing these things?

I realize that you don't believe these things...but you make a good point. A lot of pilots do believe them, and you're right, there are probably examiners out there who would fail a pilot for doing these things (even though they're right, and proper).

I operated piston airplanes in an environment where duration was more important than speed; we needed to get the longest period we could out of the fuel we had available. Most of the pilots has no prior piston experience. One day I was called on the carpet and told by the manager at that particular site that he thought I was doing something wrong. After all, my fuel burns were 25% lower than anyone else there, according to the mission reports. After some discussion, I learned that this individual was afraid to lean, that he'd heard all sorts of stories about damage, and he didn't understand lean of peak operation at all. He couldn't bring himself to fly slower or use lower power settings, and didn't understand how to properly use the engine instrumentation he had available.

This really isn't uncommon; I find that two of the most misunderstood aspects of piston engine operation in light airplanes are the use of carburetor heat and the use of the mixture control. This thread is good evidence, and makes the point well. How many are never taught, and how many more are never taught properly?

[Genghis the Engineer]

In the UK SNS, I'm afraid that it can be like this - many flying schools will teach never leaning below 3000ft (and in England, that basicaly means never leaning), and I've surprised instructors before now by leaning (or using carb heat) for taxi.

That said, I don't think that I've ever come across an examiner quite so clueless, it tends to be the less experienced PPL-level instructors. Although I'll freely admit that it was only on a course in Arizona that I got taught to lean for take-off; I've never seen it used by anybody UK trained.

On the other hand, we pretty much don't do anything but "sea level on a cold day" over here - the highest airfields in the UK sit around 800ft amsl, and ISA+10 is generally regarded as a heatwave.

(National peculiarities I suppose, most reasonaby experienced British PPLs wouldn't be overly worried about landing on a wet grass runway with a bit of a crosswind - that's likely to cause severe panic attacks in most US trained pilots.)

G

[darkroomsource]

I don't think I've ever seen a POH say to NOT lean below 3000.
I've seen them say to lean above 3000 feet, but never have I seen one that says do not lean below 3000 feet. Rather I have seen them say that you might need to lean for takeoff depending upon temperature, and I've seen POH's that say to lean for taxi.

I am not in disagreement with others who have said a person must understand the systems and reasons behind what they are doing, what I have been trying to say is, with respect to CARB HEAT, which is what this thread is about.

If the POH says to use Carb Heat on the final approach, it's a good idea to use it. There is an extremely broad temperature range where, when the aircraft is in approach configuration, the possibility of ice being produced in the carburetor is more likely, and that is why the manufacturer recommends using carb heat on the descent and on approach (for many aircraft, there are some that carb heat is not recommended)

If you teach students to follow the POH checklist for landing, and enforce this routine, they will grow up to be pilots who follow the checklist, and are thus less likely to have an engine failure on a go-around.

As an aside, I once saw a flight school that had installed "fake" landing gear switches in their C-152s, so that students learned from lesson one to lower the gear prior to landing. This, obviously was to instill in them the U part of the mental checklist. I have thought that was brilliant until recently, as I've seen that a large number of pilots are real good at GUMPS, or AGUMPS, or whatever they use, but do not look at the checklist. I fear this could cause problems down the road if such a pilot is flying a plane that requires a boost pump for go around, but learned in a plane that did not require the pump.

I think it is wrong to tell a student that they should think about the systems, and make a decision as to whether or not to use carb heat based upon the situation - WITH RESPECT TO FINAL APPROACH - rather than follow the POH. I think we can not expect pilots to be smarter than the engineers, nor can we expect in an emergency for them to be thinking clearly about things like carb heat, rather we should expect them to follow the checklist.

[SNS3Guppy]

National peculiarities I suppose, most reasonaby experienced British PPLs wouldn't be overly worried about landing on a wet grass runway with a bit of a crosswind - that's likely to cause severe panic attacks in most US trained pilots.

I seriously doubt that, but then I learned to fly in the US in a cub, mostly off gravel and grass.

In the UK SNS, I'm afraid that it can be like this - many flying schools will teach never leaning below 3000ft (and in England, that basicaly means never leaning), and I've surprised instructors before now by leaning (or using carb heat) for taxi.

There are certainly times to lean and not to lean. Where instructors have been surprised at leaning for taxi, one would expect that the same instructors would be surprised at learning to do a proper idle mixture check before shutdown, and perhaps even more so to learn that their idle mixtures were running rich. While one can't fine-lean on the ground at idle, one can aggressively lean to near starvation to prevent fouling plugs from a rich idle mixture. One should do this, too.

Conversely, when leaning for best power for takeoff, especially in notoriously underpowered airplanes such as the 172, one needs to know enough about the carburetor and systems to understand that one has to enrich the mixture before retarding power, because of the economizer function of the carburetor at high throttle settings. This is another case where systems understanding and knowledge is important. The mixture on carburetted systems equipped with enrichment or economizer features will get rich with high throttle settings, and lean when the throttle setting is reduced. If one has leaned for takeoff during the engine runup, typically at 1700 RPM, then one hasn't actually leaned for takeoff. That needs to be done at takeoff power settings, and one must enrich the mixture under those circumstances before reducing power after takeoff.

Then again, many other common wives tales abound, such as the notion that an engine is likely to quit during the first power change (reduction) after takeoff.

There is an extremely broad temperature range where, when the aircraft is in approach configuration, the possibility of ice being produced in the carburetor is more likely, and that is why the manufacturer recommends using carb heat on the descent and on approach (for many aircraft, there are some that carb heat is not recommended)

Carburetor ice is more likely in approach configuration? Really? Who told you this?

Do you understand the mechanism of carburetor icing?

The use of carburetor heat during an approach, when recommended to be left on, is done for one of several reasons, bearing in mind that the manufacturer has no idea the flying conditions under which you'll be operating. During an idle descent and approach (poor practice), one is running at reduced temperatures with reduced carburetor heat available. The effects of carburetor heat may take longer to remove ice (carburetor heat is intended to prevent, not remove ice). Carburetor heat is also used to prevent throttle plate bypass icing of the idle jet during the descent (a problem which goes away once the throttle is opened, because the idle jet is no longer in use). Carburetor heat during an approach is sometimes viewed both by operators and by manufacturers, as a form of "insurance. That is, it's used in a similar fashion to ignitors on a turbine engine during the approach phase; is the engine more likely to flame out during this time? No. Is it more likely to develop carburetor ice during this time? No. The airplane is, however, being operated at decreasing proximity to terrain with less altitude and less time to handle a problem if one develops.

Being configured for landing has no bearing on the development of carburetor ice. The carburetor has is not affected by the position of flaps or landing gear. Perhaps you meant to refer to an idle approach, when you mistakenly referred to being configured for landing. An idle approach is a poor practice in piston airplanes. Good practice for emergencies and forced landings, but poor operating practice in general. So far as the power setting, one can make an approach, especially in light airplanes, at high or low power settings, depending on the type of approach and landing one intends to do. One drags the airplane in under high power on a short field or soft field approach (the same thing in actual application in many circumstances, given that many short fields are soft, and visa versa).

If the aircraft manufacturer recommends applying carburetor heat during the approach, by all means do so, but think, don't blindly do. Are you in the desert in nearly zero humidity where carburetor icing isn't an issue (but blowing sand and your now-unfiltered induction air is an issue)? Do you really need to make the approach with carburetor heat applied? No. Are you flying an airplane in which carburetor heat isn't specified by the manufacturer, but are flying in conditions very conducive to the formation of carburetor ice? Probably a good time to use it, whether it's called for, or not.

At least for the present time, the airplane you're flying is still considered a manned airplane. You're there for a reason, and it's not simply to act as a programmed machine. You can think, you can know, you can do. You can judge, and use judgment.

The original poster asked about carburetor heat during the approach, and during the go-around. One may find that pushing power, pushing carb heat to cold, and enrichening the mixture is best broken down into several steps. One may find that shutting off carburetor heat early during an approach could be a fatal flaw in the event of a go-around. I've experienced such a circumstance (albeit not fatal) when the engine failed as I pushed up power due to a rapid onset of carburetor icing. I was with a student at the time, in a cessna 150, and it was a cool, early morning following a rain. High humidity and ideal conditions for carburetor icing existed. We made the descent and approach with carburetor heat. The student was out of place for the landing, and I directed the student to go around. The student pushed the carb heat to cold, pushed in the mixture slightly (not rich, as it was still at a high density altitude, in the mountains), and powered up. The engine began to run rough shortly thereafter and then died. I quickly applied carburetor heat, and we began to descend again without power. The engine recovered shortly before touchdown (in a lake). Subsequent approaches saw the student increasing power before removing carburetor heat, with much greater success.

Follow the manufacturer guidelines, but know the airplane and handle it accordingly. It's a fine thing to rabble on about the collective brain trust that build your airplane. No doubt the makers of the Hindenberg were a fine lot too. A great deal of educated effort went into the construction of the DC-10, and despite all that effort and all the many hundreds of thousands of hours of experienced on the type and airframe, a procedure for complete hydraulic loss was never considered or implemented until it happened to United Airlines Flight 232. You see the point, perhaps.

The manufacturer is not flying your airplane. The manufacturer did not know the operating conditions under which you would conduct your flight, here and now, when the operator built the airplane. We fly in the real world, not in the imaginary world that existed in the drafting room and on the drawing board when the airplane was built. Teams of engineers put their collective degrees and learning together to come up with the 200 series Cessna...which had no prohibition against slips. None the less, experience proved that the vertical stabilizer attach brackets were too weak for slipping, and were eventually replaced with steel, vs. aluminum. I happened to be working on a fleet of 206's and 207's, and saw many cracked brackets, and replaced them with steel ones. While the manufacturer does it's utmost, the manufacturer is not flying your airplane. You are.

Cessna warns against slips with full flaps in a number of their airplanes. The understanding of the flying light airplane public is fairly limited with respect to this caution, with some seeing it as a stern edict from above, while others see it as a meaningless notice of liability. Yet others know and understand the reasoning, and employ logic, experience, training, and understanding in the matter to operate the airplane reasonably, safely, and manage to use the full utility of the airplane.

An old asian proverb says that when one undertakes the study of a flower, it's just a flower. As one delves deeper into the study of the flower, it becomes more than just a flower. When one has mastered the flower, it's just a flower again. We all see our subject through different eyes, though it's the same material. We see it from the perspective of different culture, different training, and different experience. If you feel imprisoned by the strictures of the handbook, and if you feel that these were written by the very finger of God, then you're bound of course, to adhere to what you see, giving it no more thought than one might to the reason leaves fall from trees or waves form in a pond. It just is, it just does, it just must. Over time, given changes in one's experience and view, your own point may change. Or, it may not. Time will tell.

Too many feel bound by the checklist, as though it's law. Few understand that one can write one's own checklist and follow it. Many companies do just that. One need not adhere to nor follow the checklist provided by the manufacturer, and many don't (although most do create their checklists based on the manufacturer's data). Students often don't understand this, in fact, many instructors often don't understand this. Many seem to believe that checklists form in the cockpit as the result of divine providence, distilled from the dew of manufacturer heaven. Much of what the manufacturer provides, save for limitations, exists as a guideline, and this certainly includes checklists. Some are more sacrosanct than others, of course, and procedures are different in discussion than techniques, and of course different from limitations. Some are there to be followed without exception (limits), some are there to be followed in substance by immediate action and later by referrence to checklist (certain emergency procedures, for example, within limits), and yet others are there to be followed with wisdom as guidance.

The manufacturer includes the use of carburetor heat in describing the landing procedure, as well as the use of flaps. Can the landing be made without flaps? You bet Can it be made without the use of carburetor heat? You'll have to consider the conditions under which you're operating, because there may be circumstances under which you're better off not using the carburetor heat (under certain conditions one can put the carburetor into the icing range by use of carburetor heat...is that something of which you're already aware?). Use it, but understand why you're using it. Understand the reasons, the limits, the advantages, the disadvantages, and the subtle differences that bridge one to another (such as when to terminate it's use at the bottom of the descent.

It is, after all, still a manned vehicle you're operating. Treat it accordingly.

[Aerozepplin]

Pilots really believe that one can't and shouldn't operate lean of peak?

Lycoming's official view is still "never lean of peak", right under a graph showing the rapid reduction in CHT when one does which made me chuckle. I often feel like people are worried about "overloading" a pilot's little mind, but that the half-truths that get told make things more dangerous.

[SNS3Guppy]

True.

Then again, the most dangerous component in the airplane continues to be the pilot.

[Cows getting bigger]

100% with SNS3Guppy (well, apart from the fact he doesn't know how to spell aeroplane ;) )

[172_driver]

National peculiarities I suppose, most reasonaby experienced British PPLs wouldn't be overly worried about landing on a wet grass runway with a bit of a crosswind - that's likely to cause severe panic attacks in most US trained pilots.

I admit, too, that I was never taught proper leaning techniques. Learning to fly in northern Sweden we were never limited by performance and density altitude was low, so no need to lean. However we regularly flew into short fields, grass fields, pressing crosswind limits and VFR minima. I now fly in SoCal, a student of mine refused to land the plane on a 4000 ft rwy, wind gusts up to 20 kts but only 8-10 kts across, no coaching in the world he would do it. Different climates make you proficient in different areas.

I am all for knowledge and applying this to your practical flying. But in practice, the way training courses are laid out for PPL (but even CPL), how many people are really aware of the carburetor, accelerator pump, diffuser, fuel enrichment jet etc. How does the mixture change with altitude, carb heat etc? I doubt very few people do. Can you blame them solely? I think not, they were never taught, sticking to what the checklist says creates a standard which is SAFE, they will not kill themselves nor damage the engine.

But limited knowledge has its limitations. We regularly practice manoeuvers (stalls, slow flight, steep turns) at up to 7-8000 ft. Temperatures up to 40 deg. C on ground. Our "procedures" say mixture rich. An instructor friend of mine had an engine failure (or very poorly running engine). Engine failure checklist says mixture rich. But control of power was not regained until he leaned it sufficiently to obtain a combustible mixture.

[DFC]

I bet you'll find a lot of examiners who will fail you for leaning the mixture on ground (remember: you are burning vales with leaning!!!!! :ugh::ugh:), leaning LOP, not decreasing the power after takeoff (on engines without 5 min full power limit), etc.


No you will not find that proper leaning on the ground will cause a failure. By proper leaning I refer to leaning to the maximum possible for smooth operation.

You will fail if you lean very slightly on the ground and because you have only leaned slightly you can get airbourne with the mixture incorrectly set or slightly less than full power being developed.

Maximum leaning on the ground ensures that if you forget to select rich before take-off (low level aerodrome) then when you try to select full throttle your error will be obvious - to both you and the examminer.

Again leaning to the maximum on the ground but failing to enrichen the mixture before increasing power to do the power checks can be one of several issues that add up to a fail. When increasing power it is mixture, propellers, throttle - and that applies on the ground as well as in the air.

Finally, if your club procedures / training organisation operations manual specift that the power shall be reduced to something like 25"/2500 at a specific stage when operating normally then when you fail to do that on the test should you be surprised that the examiner regards this as not being good practice i.e. ignoring or not knowing the ops manual?

-----------

It is quite ironic that the access to the flight manual / POH in the UK is quite restricted when the UK is one of the few countries that permits flights to take place without having that document on board.

Outside the UK, the POH / AFM will generally always be in the aircraft. You can sit in the aircraft for hours and read the manual. If however, you find that your chosen school has it's aircraft on the ground for extended periods then perhaps you are at the wrong school? ;)

Every school that I know of can either sell you a copy of the appropriate POH or can provide you with the aircraft serial number so that you can purchase a copy from the manufacturer or other retail outlet.

There is absolutely no excuse for a student, renter or owner not to have a full up to date copy of the POH / AFM for the relevant aircraft available.

If the owner keeps their copy locked away then get your own!

Same goes for the engine manual.

----------

Finally, one small issue;


One drags the airplane in under high power on a short field or soft field approach (the same thing in actual application in many circumstances, given that many short fields are soft, and visa versa).




The shortest landings are going to follow a power off glide approach. the flatter the approach the the more the velocity vector approaches the horizontal and the smaller the roundout - all of which act to lengthen the landing distance required as well as the landing roll required.

Everyone needs to cross the threshold at an appropriate safe height unless they want to have the same fate as the pilots in a recent fatal accident where they collided with farm machinery in an adjacent field while making a very low flat approach.

[SNS3Guppy]

well, apart from the fact he doesn't know how to spell aeroplane

Perhaps a this-side-of-the-pond issue. Most that I know simply spell it j-e-t.

The shortest landings are going to follow a power off glide approach.

The shortest landings involve the slowest approach, regardless of approach angle. The shortest landings are in water or amid large, heavy objects. That aside for a safe, reusable airframe, short landings involve slow approaches and maximum routine stopping capability (brakes, spoilers, reverse, etc. Without anything but approach speed and brakes, where brakes can be used, approach speed determines touchdown energy, and thus rollout distance. Not approach angle. Nor the state of engine power during the approach, nor the glide. Simply the speed.

In a light airplane, approach speed is reduced for a short approach by making the approach behind the power curve, carrying power. Flat or steep makes no difference.

I am all for knowledge and applying this to your practical flying. But in practice, the way training courses are laid out for PPL (but even CPL), how many people are really aware of the carburetor, accelerator pump, diffuser, fuel enrichment jet etc. How does the mixture change with altitude, carb heat etc? I doubt very few people do. Can you blame them solely? I think not, they were never taught, sticking to what the checklist says creates a standard which is SAFE, they will not kill themselves nor damage the engine.

There is no excuse for an instructor to fail to teach aircraft systems and their use, nor is there any excuse for a student to fail to study them.

Sticking to the checklist blindly does not result in a safe standard, and yes, they can kill themselves and damage the airplane, engine propeller, and everything else in or attached to the airplane, as well as persons and or property on the ground.

Failure to lean on the ground, and then failure to lean for takeoff, resulted in an inability to clear powerlines in a rented Cessna 172 many years ago. I knew the pilot. He had his family on board, and they were badly injured. His wife and children survived, but took a year to recover. He was badly injured. He was only following the checklist. Where the checklist called for mixture rich, he didn't take into account that such counsel didn't apply at a five thousand foot elevation, nor nearly a nine thousand foot density altitude.

It was a nice airplane, too.

But limited knowledge has its limitations.

A little learning is a dangerous thing.

[darkroomsource]

Carburetor ice is more likely in approach configuration? Really? Who told you this?
My physics teacher, and my experience.
It has to do with the venturi effect, and the fact that as you are going slower in climb or during approach, the venturi effect is more pronounced.
Combine this with having a smaller opening in the carburetor, as a result of reducing throttle the "whole" is smaller in the throat, and you have the widest range of temperatures for carburetor icing during the approach (not necessarily approach configuration, but when you've got flaps out and gear down, you're slower)
I studied engineering at University, and worked for many years doing flow analysis of liquids for flood control districts.

[SNS3Guppy]

My physics teacher, and my experience.

You're asserting that your physics teacher was a flight instructor, and that he taught you about carburetor icing?

You've developed more carburetor ice during approaches, and thus know by experience that configuring the airplane for landing causes carburetor ice?

Are you familiar with the term "non-sequitur?"

It has to do with the venturi effect, and the fact that as you are going slower in climb or during approach, the venturi effect is more pronounced.

Now this is interesting. I was getting a little bored with this topic, as it's been fairly beaten to death, but this is different.

You're asserting that going slower causes carburetor ice? You're asserting that going slower causes a "more pronounced venturi effect?"

Have you spoken with your physics teacher lately?

Bernoulli, as passed down through your physics teacher, would tell you (if he were here to do so) that where an increase in velocity occurs, a proportional drop in pressure will be found. Thus, it's not a decrease in velocity which causes a "more pronounced venturi effect," but an increase in velocity. In other words, going slower does not a "more pronounced venturi effect" make.

Call your physics teacher. He would like to hear form you.

Combine this with having a smaller opening in the carburetor, as a result of reducing throttle the "whole" is smaller in the throat, and you have the widest range of temperatures for carburetor icing during the approach (not necessarily approach configuration, but when you've got flaps out and gear down, you're slower)

It's a hole, rather than a "whole," but we're still stuck with that whole physics thing, you see. That engineering degree isn't shining through in your description of the carburetor. The "widest range of temperatures for carburetor icing" occur because of a "smaller opening in the throat," you say. Again, interesting. Given that the temperature drop is proportional to the velocity of the airflow as a function of the pressure drop, you're still fixed on the concept that reduced velocity (and let's not forget, aircraft configuration, a true mystery player here). You're asserting that flaps and gear make for a slower airplane, which makes for a "wider range of temperatures for carburetor icing."

I'm really curious about this wider range of temperatures. Somehow, we have two disconnected concepts here. One is that being configured somehow increases the "range of temperatures for carburetor icing." The other is that being slower somehow also increases the "range of temperatures for carburetor icing."

Hopefully you'll understand that going slower doesn't increase the potential for carburetor ice. Flying an approach at a slower airspeed doesn't increase carburetor icing potential, and flying at a lower engine RPM (with a slower attendant airflow velocity through the carburetor, as well as a reduced mass airflow) doesn't increase carburetor icing potential, either. As well as neither one increasing carburetor icing potential, neither one increases the "range of temperatures of carburetor icing."

Let's examine this a little more closely. The ability of ice to form is a function of the properties of the moisture which will be doing the freezing. Unless one manages to alter the chemical properties of that moisture, then the "range of temperatures" at which ice formation will take place doesn't change. To suggest that a change in the "range of temperatures" takes place, one must acquiesce to the concept that ice freezes at higher temperatures, and lower temperatures (unless you're asserting that this range of temperatures only trends downward, but that's a problem because the temperatures aren't getting colder in that carburetor when the engine speed slows [and airflow velocity slows], and certainly not when the airplane slows). Are you suggesting that a chemical change in the moisture entering the carburetor through induction air has been chemically altered by reduced engine speed, reduced airspeed, or the mysterious magic of configuring the airplane? Say it isn't so.

Let's remember that the internal combustion engine, insofar as the carburetor is concerned, is a big vacuum cleaner. It's a suction machine. The amount of airflow through that machine increases as the speed of the machine increases; run the engine at a higher RPM, and you'll get a higher airflow through the engine with the throttle open, or a greater "suction" with the throttle closed. Therefore, at higher power settings, we have greater airflow (and faster airflow through the engine), and at higher airspeeds with the throttle closed, we have greater differential pressure across the throttle plate, with higher airflow over the idle jet (bypassing the throttle plate as a calibrated leak), and thus the greatest icing potential when diving at idle at high speeds (not slow) and when operating at higher power settings.

You said you knew about carburetor ice based on experience (and your physics teacher). How much carburetor ice experience have you had at high power settings?

I studied engineering at University, and worked for many years doing flow analysis of liquids for flood control districts.

Did the flood control districts get a lot of carburetor icing? How about the university?

[barit1]

My father and I had the good fortune of meeting Max Conrad, who set several light-aircraft distance records and made a good living ferrying Piper aircraft trans-ocean. He won the 1964 Harmon Trophy.

But the point to be made is his use of carb heat in optimizing fuel consumption. He used a substantial amount of heat in cruise to ensure fuel was completely vaporized before entering the cylinders. Thus he could lean the mixture further, there being less/no unburned/wasted fuel. I do not know his exact technique, but I believe it can be discovered in his books and magazine articles.

[SNS3Guppy]

Partial carburetor heat is the most effective use, but it does require accurate carburetor air temperature instrumentation.

The use of full carburetor heat in most light airplanes is not a function of necessity, beyond that required due to lack of instrumentation, and lack of pilot training (and experience). It becomes an all-or-nothing proposition, in which excess heat is often used, beyond that which is appropriate to put the carburetor in the ideal temperature range.

Lack of instrumentation is a function of economy, and full carburetor heat becomes a simple act of pilot-proofing the airplane, or more specifically, protecting the airplane from the pilot.

[darkroomsource]

Carburetor ice is more likely in approach configuration? Really? Who told you this?
Your lack of understanding of fluid dynamics is apparent.
Please, do not continue to teach your students to believe that you or they are smarter than the engineers who wrote the POH.

There is significant evidence that an fluid, be it air or liquid, when flowing through a venturi has a lower STARTING temperature if the slower it is flowing thorugh the opening. The increase in speed through a venturi in relation to the STARTING speed increases in inverse relation to the starting speed.
Therefore, the air flowing through a venturi is colder when an aircraft is in approach.

From my experience, working with fluid dynamics.

Additionally, from my experience, in flight, I have encountered carb ice far more frequently in climb than in cruise, when the aircraft is flying slower.

I have encountered carb ice, and for that matter, airframe ice, in clear air, on a sunny day, in the desert. And I know others who have also.

However, as you have clearly stated, you know more than anyone else about anything on the face of the planet, so I am through with this discussion.

I would suggest to any readers, that if the POH says to use Carb Heat, then do so, and teach your students to do so. It is meant as a preventative measure (unless you are actually experiencing carb ice), and does not impact the performance of the plane enough to justify not using it. Never mind that your insurance company will probably refuse to cover you if you teach a student to ignore the POH.

[Genghis the Engineer]

Your lack of understanding of fluid dynamics is apparent.
Please, do not continue to teach your students to believe that you or they are smarter than the engineers who wrote the POH.

Oh dear, I'm going to regret getting involved here I'm sure - however for the record I have a commercial pilots licence, a PhD in aerospace engineering, and have written (well, technically, led the writing of) several aircraft operators manuals, with about 1000 hrs in piston engined aeroplanes, most of that with carburated engines, and probably 400 of those in something with another venturi for some reason or another.

There is significant evidence that an fluid, be it air or liquid, when flowing through a venturi has a lower STARTING temperature if the slower it is flowing thorugh the opening. The increase in speed through a venturi in relation to the STARTING speed increases in inverse relation to the starting speed.

Err, no, at subsonic speeds (certainly below 0.6M, and probably below 0.8M) the flight speed of the aeroplane has no significant impact upon the inlet temperature. Particularly because on many aeroplanes, the intake isn't pointed into the free airstream anyhow, it's either sat inside still air inside the engine compartment, or through the prop disc.

It's too late at night to work through Bernoulli's equation, but that particular relationship is also a little more complex than you make out.

Therefore, the air flowing through a venturi is colder when an aircraft is in approach.

No, for several reasons. Firstly, airflow is a function of engine speed, which tends to be fairly low on approach. Secondly air temperature is a function of altitude, which tends to be at its highest on approach.

Finally being on approach, and being in the approach configuration are not the same thing. A flapless approach is in the cruise configuration on a fixed gear aeroplane, and offers no significant protection against carb icing.

From my experience, working with fluid dynamics.

Additionally, from my experience, in flight, I have encountered carb ice far more frequently in climb than in cruise, when the aircraft is flying slower.

In what types? - whilst I'm not denying the potential for carb icing in any mode of flight, this is very definitely not my experience.

I have encountered carb ice, and for that matter, airframe ice, in clear air, on a sunny day, in the desert. And I know others who have also.

What sort of relative humidity? This sounds highly unlikely to me; I don't dispute that you may have had an engine problem - but where did your humidity come from to form ice? Lack of humidity is a usual feature of the air over deserts.

However, as you have clearly stated, you know more than anyone else about anything on the face of the planet, so I am through with this discussion.

I'm pretty certain that's actually a fellow called Bill Brooks, who has one degree more than me, about 5 times my flying hours, and has designed and tested getting towards 20 aircraft types. SNS is a bright fellow, but he's not Billy.

I would suggest to any readers, that if the POH says to use Carb Heat, then do so, and teach your students to do so. It is meant as a preventative measure (unless you are actually experiencing carb ice),

That really does depend upon the aeroplane. For example the POH for the PA28-161 that I used to fly, specifically recommended NOT using the carb heat on approach unless carb icing is experienced. So that is cure, not prevention.


and does not impact the performance of the plane enough to justify not using it. Never mind that your insurance company will probably refuse to cover you if you teach a student to ignore the POH.

You're being a tad contradictory here - you've said you get carb icing in climb, but in that mode of flight carb heat will most definitely reduce performance in many (although not all) aeroplanes.

And I don't think that anybody has proposed ignoring the POH, so much as understanding it, and the aeroplane, and making a reasoned judgment on the basis of knowing as much as possible.

G

[Big Pistons Forever]

,
And I don't think that anybody has proposed ignoring the POH, so much as understanding it, and the aeroplane, and making a reasoned judgment on the basis of knowing as much as possible.

G

It is sure nice to see someone who can take a 5 page thread and distill its essence into 3 lines. Well done

[SNS3Guppy]

Additionally, from my experience, in flight, I have encountered carb ice far more frequently in climb than in cruise, when the aircraft is flying slower.

It's a shame that you're done with this conversation, because you really need to explain how you were previously able to tell us that being configured for landing produces the widest range of carb icing, and that in your experience, carburetor ice is more likely in approach configuration because your physics professor told you so.

The problem is that now you tell us that it's not really the approach configuration, or the idle descent to approach, but in the climb where you've experienced carb ice the most.

Given that this is contrary to what your physics professor taught you, and contrary to what you previously told us has been your experience, I'm very curious to know which manufacturers recommend using carb heat in the climb. After all, you're adamant that these are the folks with all the degrees (in carburetor icing??), and that they know best. The problem is that I don't think I've ever seen a manufacturer call for carb heat in the climb as part of the climb procedure. Are you now telling us that all the engineers and the manufacturers are wrong?

Does your experience teach us this?

It's really a shame that you won't be a part of this conversation any more, because I'm entranced by your latest turn. If by any chance you reconsider, I await with rapt attention and baited breath. You're fascinating.

[LH2]

as a result of reducing throttle the "whole" is smaller in the throat

Perchance you mean the "hole"? :hmm:

I would not normally point that out, but...

I studied engineering at University, and worked for many years doing flow analysis of liquids for flood control districts

Well, given your spelling and your manner of expression, I think the above statements are liable to qualification, if not outright questionable.

And just what is your flying experience, btw? (not that I'm interested) :rolleyes:

[CREAMER]

I learned a good lesson today. In future I will be keeping carb heat applied until landing.

I fly an aircraft with a Continental A65 which has a reputation for being susceptible to carb icing. The conditions today were Temp -1deg C, Dew point -2.5deg C and RH 89%.

I initially flew two circuits. I gave a good dose of carb heat throughout most of the circuit but went to cold in the last 200 feet (for that one in a million go around). My first touch and go was uneventful. On the second circuit, I reduced to idle for the touchtown. The touchdown was uneventful but a few seconds later the engine stopped dead. I turned off the runway and restarted the engine without difficulty.

My first idea was that the idle speed was set too low but when stationary the engine idled ok.

I took off again, did another uneventful touch and go but again, on the second, the engine died after touchdown. I decided to give up after that, thinking that I would probably have to make some adjustment.

After discussion with two other instructors and having ascertained the conditions, we deduced that icing must have caused the problem. In fact, others had been experiencing icing on slightly more advanced engines today.

I was surprised at how quickly the ice must have formed and I am glad that I did not reduce to idle at about 100 feet (for some reason).

I am sure that with the aircraft stationary, there was enough residual heat from the engine to melt ice without the super cold airflow there.

On reflection, I don't think that there is a good reason to go to cold on final approach. If you have to go around you can put the carb heat to cold then. I don't even remember being taught to do this when I did my PPL in 1980. I do remember it being taught when I did a refresher in 1997. I guess it's one of those faddy things that crept in. Sadly it may cause more trouble than it solves.

I hope this helps and apologise if I have repeated too much of what is in previous posts.

[FormationFlyer]

Ive resisted until now...due to the large amount of hot air being exchanged - and exasperation that this debate goes on year after year after year. Sorry folks but 15 years of this debate (for me) is madness and *still* pilots lose engines due to carb icing - I suspect this is directly down to the community and instructors failing to teach to the published recommendations. :ugh:

The CAA's guidance is straight forward and presented in two excellent documents - which I'm surprised to note haven't been mentioned.

AIC Pink 077/2009 Induction System Icing on Piston Engines as Fitted to Aeroplanes, Helicopters and Airships (http://www.nats-uk.ead-it.com/aip/current/aic/EG_Circ_2009_P_077_en.pdf)
and
Safety Sense Leaflet 14 Piston Engine Icing (http://www.caa.co.uk/application.aspx?catid=33&pagetype=65&appid=11&mode=detail&id=1168)

Also the Lycoming service bulletin previously stated in this thread is excellent.

Icing conditions are present in the UK 100% of the time - its a question of severity rather than existence.

The recommendations are very clear. Carb heat on until touchdown.
It does say..."On some engine installations, to ensure better engine response
and to permit a go-around to be initiated without delay, it may be recommended that the carb heat be returned to COLD at about 200/ 300 ft on finals." Unfortunately many pilots/instructors seem to believe (wrongly) that their aircraft is one of the exceptions. Why I have no idea.

The arguments about the go-around and loss of power on Cessna or Piper aircraft I believe is ridiculous - and such debates Im convinced are downright dangerous as we appear to be encouraging pilots not to err on the side of caution.

In aircraft where you can increase power and put the carb heat cold simultaneously do this simultaneously (C152 etc). In aircraft that this is not possible in (PA28) Apply power FIRST then move the carb heat to cold. This takes about 1/2 - 1 sec. The loss of 50-200rpm in this time is is reality inconsequential - the aircraft will as a MINIMUM fly level and in all but rare cases will climb with the resultant power on every aircraft I have flown. Comments about detonation (the dreaded carb heat and full power) in the space of 1/2 - 1 sec are also unfounded - especially as the engine itself will have been cooling (to some degree) during the descent anyway.

CREAMER - you situation is not unusual. Over the years I have come to know 2 instructors who have had engine failure actually on final approach in PA28s with Lycoming engines. I know another instructor who had engine failure on final approach in a Cessna 152 again with a Lycoming. All 3 made it to the runway thankfully.

I recommend that all pilots stop this continental vs lycoming myth as well - carb icing happens on majority of engine installations - play safe - use carb heat!

Personally I will teach in accordance with CAA recommended practices, and encourage ALL pilots to do the same.

I have yet to have an engine fail due to carb icing. Nor am I aware of any of my students having lost power due to carb icing and I plan to keep it that way. :ok:

[SNS3Guppy]

I have yet to have an engine fail due to carb icing. Nor am I aware of any of my students having lost power due to carb icing and I plan to keep it that way.

No need to apologize for lack of experience. Simply because you haven't experienced it yet isn't an indictment upon those who have.

Icing conditions are present in the UK 100% of the time - its a question of severity rather than existence.

An excellent observation, and one that applies outside the UK, as well.

The recommendations are very clear. Carb heat on until touchdown.

A blanket statement, and therefore only applicable some of the time.

Not all situations require it, not all aircraft require it. Some manufacturers recommend against it, as we've previously discussed here. In aircraft utilizing a carburetor air temperature gauge, the use of carburetor heat less than, or in excess of that required to place the carburetor air temperature in the proper operating range is inappropriate, and wrong.

I fly an aircraft with a Continental A65 which has a reputation for being susceptible to carb icing. The conditions today were Temp -1deg C, Dew point -2.5deg C and RH 89%.

Sounds like ideal carburetor icing conditions.

I learned to fly in a J-3 cub. One had to lean forward to pull the carburetor heat, and lean forward to push it off. Doing so in a go-around wasn't practical, really. Our policy was to apply carburetor heat prior to the power reduction abeam the numbers, for fifteen seconds, then shut it off for the descent and approach.

The only engine failure I had in a cub occurred on short final when I pushed the power up too fast because some deer ran onto the runway. Lacking an accelerator pump, one needs to be judicious with throttle application in that airplane, and the result was too much throttle, too quickly, and the engine complained. I never saw any issues with carburetor ice at that operation, in any of the airplanes. That's not to say that it wouldn't have been experienced there or elsewhere, but at no time did the policy of applying carburetor heat before the descent in the patttern, and then shutting it off, cause us a problem.

It can certainly cause a problem in other settings, other aircraft, other circumstances; one shouldn't apply that policy or procedure from that one location in that one airplane (it was standard fare among the other airplanes there, too...aeroncas, cubs, cessna 120's, etc) to your flying. Likewise, however, one shouldn't apply the blanket notion that carb heat must always be used for the descent. Then again, one shouldn't get in the habit of doing idle descents in light piston airplanes, either.

[FormationFlyer]

SNS3Guppy - Agree totally. Don't confuse not experienced carb icing (which I have many times) with not having an engine stopping. Simply because you haven't experienced it yet isn't an indictment upon those who have.
There are many reasons why engines stop due to carb icing - much of it though IS down to pilot error. Indictment? hardly. I'm not here to put people down. I'm here to make sure we all stay living.

The blanket statement of course comes with the caveat unless contradicted by FM/POH. Don't take my word for it though. Please read the full background material - that is what I am suggesting. I am merely paraphrasing here.

In the J3 you are right - and a sensible move to take the carb heat away at suitable height.

But thats what this is about isnt it? Use the standard advice UNLESS the FM/POH or operational issues mean that the standard advice is not practical. Here you quote one of the exception due to practical operational reasons. I still believe that the number of these exceptions is relatively low - and indeed tend to exist on older a/c types such as the J3.

Why is it though that CREAMER experienced his issue? (please comment creamer). Was this a lack of training in general procedures? Lack of training specifically on type? Was CREAMER's training performed in an a/c that was fuel injected and then they famil'd onto the Cessna and the Famil training was lacking?

I'd love to know. I want to know where this problem could have been avoided - Because CREAMER should never have experienced this issue to start with.

I love the CAA's old slogan. "Safety is No Accident". It was very clever in its double meaning. I don't know why they don't seem to use it so much any more but its one that I hold dear. So I like to focus on avoiding problems and making flying safer.

[DFC]

The situation is very simple.

By all means follow the advice in the POH and don't select Carb heat during the approach.

When you have an engine failure due to carb ice on an approach or in a go-arround then don't blame the manufacturer or the author of the POH.

The answer will simply be that it was your fault because clearly the conditions existed for carb icing and that is why it formed. By not following the advvice in the POH to have hot air selected in such conditions you caused the accident.

99% of people having problems making a go-arround have overloaded the aircraft fro the conditions. Every aircraft shoulld have a suitable balked landing performance - that is with gear down and flap for landing. While having hot air selected may reduce this performance temporarily until it is selected cold, the fact that the aircraft can climb with drag flap means it will climb a lot better with approach flap.

So who is now going to ignore the POH advice and only use partial flap settings to land?..........oh sorry, plenty of people doing that already...........and plenty more loading aircraft to such an extent that the balked landing performance is nil.

Pipoer are very clear, if the conditions are suitable for formation of ise then have the hot air selected during approach. Clearly if you don't and the engine fails it is your fault for not recognising the situation.

This is the situation in the UK for most of the year.

[CREAMER]

In my case, I probably got caught out because my training said that I should select carb heat at 200 feet. This was on club aircraft (C152) during a refresher and Instructor Course.

Translate this now to an Aeronca with an A65 in fairly typical winter conditions very conducive to carb icing. You just can't do it. In fact, if I fly a C152 again I will still keep carb heat to touchdown. If the CAA are saying this as well then we have little choice (in court).:=

[FormationFlyer]

I just want to point out that the original question here was one of instructor standardisation in a school in the UK. It was a discussion by an instructor who wanted to consult fellow instructors and examiners.

How did we end up with comments about some dratted 'physics teacher?'. Laughable - and detracts from the importance of this thread.

For those who are not flying in the UK or used to permenant carb icing conditions the biggest cause of engine failure in the UK is carb icing, followed by mismanagement of fuel systems. In other countries where carb icing conditions are mild most of the time I would imagine fuel mis-management is probably a bigger issue.

There is a myth that PA28s don't carb ice - they do (ive had it in IMC, ive had it on the ground before night flying during the taxi etc). There is a myth that C150/152 on continentals are terrible but you are OK on a lycoming - you arent. Ive had carb icing on C152 with Lycomings.

The point about I was making about the instructors who had engine failures is this - all 3 of them without exception now take carb heat to the deck. I like to learn from others experiences - I read GASIL and associated accident summaries religiously. I go to a CAA safety evening every year - even though some might expect that as an experienced instructor and examiner I might not. Personally I recommend everyone attends - they are good (and as a side note it was nice to see David Cockburn's hard work recognised).

DFC - absolutely.
CREAMER - thanks for the info. Most interesting.

In the UK the most common training aircraft are PA28s, C150/152/172 and Robin aircraft. The CAAs advice holds good for all these aircraft.

I believe its an absolute must that we instructors standardise our teaching practices - particularly within the same school. I believe the basis for that advice should start with the CAA AIC & Safety sense leaflet further modified by the FM/POH and engine manufacturers advice - as pointed out (quite rightly) every aircraft is different. What we as instructors must teach and prepare students for any aircraft - but equally we must give the 'basic' advice on the cautionary side.

[DFC]

To look at the issue from a different perspective.

When descending from 5000 to say say 2000ft does anyone not use carb heat when the power is reduced - and keep it hot until power is increased?

So there is absolutely no perceived problem with quickly establishing full power if an urgent climb is required at 3500ft - to avoid another aircraft for example?

If someone is teaching to put carb heat cold at 300ft in case of go-arround then what about the go-arround from 600ft?

How many instructors here teach that the power off fully developed stall or any other stall exercises where low power is used should be entered with carb heat cold - just so that max power can be established on recovery?

If the stall warner goes off at 350ft (for those that select cold at 300) do you not simultaneously reduce the AOA and apply full power?

Many actions in these critical situations such as reduce AOA, full power (throttle full, carbheat cold) have to be automatic to be effective.

[SNS3Guppy]

When descending from 5000 to say say 2000ft does anyone not use carb heat when the power is reduced - and keep it hot until power is increased?

Of course I don't use carb heat as part of a routine, normal cruise descent.

Are you making idle descents?

In other countries where carb icing conditions are mild most of the time I would imagine fuel mis-management is probably a bigger issue.

Carburetor ice is a geopolitical issue, now?

[johns7022]

Guppy...you must be here to confuse the kids.....

OP: Power out of the green...in a decent...carb heat on....

I would elaborate...but Guppy and I will get into it.

[FormationFlyer]

Carburetor ice is a geopolitical issue, now?

Dear oh dear. SNS3Guppy that is just a silly comment that suggests belligerence. Shame because I'm sure you have a wealth of real experience to share instead of unwieldy attempts at points scoring.

I thought we were experienced instructors and examiners on this forum and therefore did not need explain the basics behind such a comment in detail, but as you obviously feel the need to have me justify the context of the comment Ill indulge you this time.

Whilst Carb icing is *not* geographically confined by country NAAs are and thus accident/incident statistics etc are as well. The statistics are collected by the NAAs and thus it follows that the most common cause of engine failure may differ between countries for a variety of reasons.

Additionally advice and guidance issues forth from those NAAs to be applied by the pilots and on aircraft operated within their jurisdiction. This may have an effect and thus may effect the statistics for a given NAA.

Where I refer to carb icing conditions being mild I was asserting that it was unlikely that carb icing is likely to be the most significant cause of engine failure. Additionally whilst carb icing is a global issue the prevalent conditions in a given country will be influenced by their geographical location. In the UK we experience high humidities as any air mass inbound to us tracks over water.

I hope this clears up any possible confusion that I may have caused.

[SNS3Guppy]

The statistics are collected by the NAAs and thus it follows that the most common cause of engine failure may differ between countries for a variety of reasons.

Given the commentary here and on the private pilot forum, I'd say that the sampling on this site clearly shows the reason for the geopolitical difference isn't climatic, but the lack of proper training. Poster after poster has acknowledged the scant receipt of carburetor training, systems training, or even the availability of a pilot handbook during their training, rental, or use of the airplane.

No wonder that incidents occur given the lack of proper training.

[ADB25]

So am i correct in saying, on approach and really any type of decent it is a good idea to set carb heat on?

[Genghis the Engineer]

So am i correct in saying, on approach and really any type of decent it is a good idea to set carb heat on?
Depends upon conditions and aircraft type.

G

[Teddy Robinson]

Generically what we are seeking to achieve through training and good practice is to minimize the risk of carb ice causing an accident through not applying it, and the probability of a performance related accident by insisting on it's use when it may not be appropriate.
To an extent, this comes down to a critical question.
Do we teach down to a price or up to a standard ?

Many professional schools have an SOP which says that at around the selection of final flap, carb heat is selected to cold, which given the likely power setting will give adequate protection under most circumstances within the VFR circuit environment.

This is mirrored in the airline ice protection culture, that the protections are removed to ensure performance to clear the spiky bits in the event of a go around/ balked landing.

TR

[Pilot DAR]

I admit to not having read all of the foregoing posts. I know I owe it out of courtesy, but it's just too much!

Without being contencious, or wanting to apparently conflict with SOP's, I do things differently. Feel free to discard my comment, and remain with your training, or SOP, but know that others do it differently.

I use carb heat if the atmospheric conditions warrant it. I do not use carb heat by rote. I opine that it is very unlikely you will accumulate enough ice to be a hazard, during your brief time in the circuit, if you were not accumulating it in cruise flight. If you needed the carb heat in cruise, you're going to need it on approach. If you did not need it in cruise, why would you need it in the circuit to landing, unless there has been a big change in conditions or temperature due to lapse rate? If you apply carb heat with low power and a rich mixture in most types, you're hardly creating enough heat to melt any ice anyway! I nearly never use carb heat in most types I fly, other than to check it's operation and effectiveness. If conditions are conducive to ice, I use it, and carefully adjust power to compensate for it.

If carb heat is really necessary to de ice, or prevent ice, you're probably going to need to optimize the heat. This will involve some reduction in power, to reduce the mass airflow, (mass of air to be warmed), and peak leaning, to get the most heat out of the engine you can. Cabin heat must also be off (unless a separate heater). A carb air temperature indicator is also worthwhile.

People are going to disagree with me on this, and that's fair enough. However I hold the opinion that the use of carb heat is often by rote, for no valid reason, and more an anti liability cautionary acvtivity, than regularly necessary. I believe that like any control, you should be using it (or not) because you understand why, and that you need it! Not just because it was taught, and you never knew... If you're selecting it, with no more thought, you're probably not getting the most heat available, fouling plugs with an overly rich mixture, and giving one more thing to overlook during an overshoot.

Follow your instruction, and the flight manual, but try to actually understand too...

[rotorfossil]

It's interesting to read about the different carb heat cultures between helicopters and fixed wing. All carburettor fitted helicopters to my knowledge (and I've flown most of them) have a carb temperature gauge and the teaching is simple - keep the needle out of the yellow band, which means in temperate climates using it all the time.
What varies and causes confusion is whereabouts the temperature is sensed. For instance on the old Bell 47's, it was sensed at the intake and the yellow band was up to +32deg C. On the Robinson's it includes a sensor after the throttle butterfly and the yellow band is up to +5deg C. Whatever, if you obey the rules of usage, you don't get carb icing and there is none of the hit or miss techniques that fixed wing have to use (and I fly those as well). What is often not appreciated is the 25deg C odd drop in temperature between the intake and the back of the the butterfly in partial power conditions. Also how do you assess which conditions are conducive to carb icing. For instance very cold temperatures are not, as there is too little moisture in the air. On the other hand, what about a warm but very humid day when the temperature is not much below 25deg C.
When some test were conducted on a carburettor rig made of transparent material, I understand the biggest surprise was the speed the icing developed after start, ie about 5 seconds - food for thought!

[rhwheeler]

"Landing Approach – In making a landing approach, the carburetor heat is generally in the “Full Cold” position. However, if icing conditions are suspected, apply “Full Heat”. In the case that full power needs to be applied under these conditions, as for an aborted landing, return the carburetor heat to “Full Cold” after full power application."

It is noted that if icing conditions are suspected the engine manufacturer's service instruction is to apply full power then set carb heat to cold for an aborted landing.

It would be difficult to argue that icing conditions in a temperate climate should not be suspected!

In the case of a go around from a FLWOP this is especially important.

[Pilot DAR]

I don't know of an airport with FLWOP as an identifier. I presume it's in a humid temperate place?

[24Carrot]

I don't know of an airport with FLWOP as an identifier. I presume it's in a humid temperate place?

If he was worried about the go-around, I think it must have been at PFLWOP ;)

[Big_Buddha36]

Hi,

A lot of replies on this one, so I'd rather post my personal thoughts as an instructor, rather than details of school-a teaches x, pig says y

I much prefer bumpfichl to be a carb-CHECK not just set to hot until later - why? Because I prefer 1 procedure for 1 job. The throttle and carb are intrinsically linked and but breaking this connect in the mind, you risk forgetting it. I prefer, therefore to stick with carb hot, as you power down on the base.

As for when to go back cold. Many say/teach go carb cold at 300" for the go-around. Now, whilst you can argue you could glide etc, I was told be a senior examiner that did my f.I test. He went carb cold at 300" and as the wheels touched, his engine stopped with icing.

So what some say! But in reality, what he did by going cold, was remove his option of a go-around. I prefer therefore to land carb hot, clean up, full-power&carb-cold.

There, my 2pence worth on a subject I bring up at my school regularly (without success!)

Bb

[Pull what]

What a ridiculous argument-the most important point here is that your instructors are not follwing a common standard-potentially much more dangerous than splitting hairs over when and where to apply carb heat.

The role of the CFI is to set the training policy based on the engine manufactures instructions and any directives published by the CAA. The role of instructors should be to follow that policy or work elsewhere. Schools that operate with instructors doing their own thing, usually based on folk lore, only serve to lower training standards.

[Big_Buddha36]

Pull: I'm sure I'm going to speaking out of turn here, but I would suggest that teaching as per the school and AGREEING with that can be 2 completely different things.

Icing can occur at any phase, so I prefer to advise not to just assume carb is required ONLY when at low rpm. I personally have no problems with placing carb hot and leaving it during
Bumpfichl (as per the school) but I also acknowledge a risk of forgetting to carb cold due the dis-connect.

I do think it's daft not to take into account actual events you are aware of. My own training left carb hot until go-around, the examiners story re-outerwear that for me and whilst I teach as per the school to carb-cold at 300" final checks, when I'm flying myself I tend to leave it as I was taught.

I guess what I'm tying to say is that you
Could have the same argument over how best to fly a pfl etc. I think want you can also get from this thread is not only
Your point about instructors formulating their own methods, but also (dare I say) that the CFI isn't always right. The reason why this thread exists in the 1st place is that how to fly is an educated set of opinions. If there was a "right" way, we would all have a specific method - no variation possible (which we obviously do get!!)

I think this thread is simply trying to determine the consensus on when, not who's being naughty. If you can't, as an instructor add your own experience into the guidance you give, I think that is actually the step back. Don't forget, the young low-hours instructor may actually be right - will the CFI listen?

Again, please don't take anything I say here as disrespectful or argumentative - I'm just playing devil's advocate:ok:

[Big_Buddha36]

Formation: you've cheered me up no end this evening. You obviously have much more experience then I do, but it's pleasing to know I've come to the very same conclusions/arguments over this as you have, using just plain old common sense (on my part)

I totally agree about being aware of icing at ANY time. That we can teach without thinking why. And that for the anecdotal evidence ive seen here and before, that landing carb hot for the sake of 1/2 sec of go-around at 95% power as you go cold is better than losing that oPtion all together.

Perhaps we need to live in a world where the schools canvas the staff on the how-to's rather than leave it to 1 person to formulate (the CFI) - just a thought. :}

[Pull what]

Ive worked at schools which have no standard policy implemented by the CFI and it just confuses the student, as this is the sort of low standard school that always swaps the stude to different instructors who then go about saying-"no dont do it that way do it this way". Its a bit like trying to act out a play with everyone directing themselves, it cannot work.

I cannot quite agree with the way you phrased that, quote Icing can occur at any phase,.

Thats an ambiguous statement that needs qualifying.

[Big_Buddha36]

Pull: I believe the question was when to use carb hot? Not what each school does. My point is that what I do and what I teach are different.

And not sure what's confusing about when I think you can get icing ? Up, down, straight along. PTA not the preserve of lower throttle settings, simply that a smaller throttle will allow more chance of it being an issue, no.

I've had icing on the ground, I've had it during the cruise, not personally in the decent bit then I use carb!! :} and I see no reason why it can occur in a climb. Just because a throttle is wide open, see no reason why it can't form - no??

[Pull what]

OK-so you if were in an area of CI would you tell your student to descend throught it with low power or high power-using your statement it would make no diiference

[Big_Buddha36]

Pull- you misunderstand me. I'm not saying throttle position makes NO difference, just that icing Of varing impact could occur at any time. We do FREDA during the cruise and that's with the throttle fairly wide open. Fully open would be better than idle to stop ice closing Off the throttle, but it can still begin to form at differing throttles, differing days, temp, RH's etc. There's no set rule - I simply said I prefer the general "throttle back, carb hot throttle forward, carb cold". I also personally prefer to land carb hot (esp. in colder, high humidity conditions) but that's me. The school I work for teaches carb hot and remain on the downwind , carb cold at your final 300" checks ;)

[barit1]

Jeez - I cannot believe this. With throttle at idle, i'd keep carb heat ON until GA. It can'r take more than a second or two to turn off carb heat after (or during) throttle advance. At least this way I have the best assurance the engine(s) WILL respond. Can you say OBVIOUS?? :ugh:

[Big Pistons Forever]

The "carb heat off at 300 feet" procedure seems to be the UK SOP. However in North America, and I would suspect the rest of the world, the near universal SOP is to leave the carb heat on and if an overshoot is required, to select cold after full power is applied.

So my question is where did this procedure come from, the CAA, a big flying school, a text book ......:confused::confused:

[mrmum]

The carb heat off at 200-300ft, is indeed widespread normal practice in the UK in common SEP training types. However, personally I don't like it and haven't done it for years, not since I stopped working for other people and got to make own rules/SOPs. I suspect a lot of people who advocate it, haven't been caught out by serious carb icing.
On my PPL we only used carb heat on glide approaches, not at all on normal ones! I can't remember what I did on my BCPL, but on the AFI course (as it was then), it was carb heat on all the way to the ground or go-around.
In the two clubs I worked for I had to fit in with the standardisation of carb heat off at 200ft. My first job included instructing cadets for the MoD Flying Scholarship Scheme, IIRC when the RAF CFS came to approve us they insisted on the 200ft carb heat cold procedure, so perhaps originally it stems from the military. Interestingly, we used Cessna 152s for this and it's contrary to the C152 POH I think, which says carb heat to cold after landing.
I don't recall seeing in the POH for anything I've flown regularly, a procedure for knocking the carb heat off at 200ft, although someone may be along shortly to quote one. As I recall they often say something like use carb heat if icing conditions are encountered/suspected, which in the UK is pretty much all the time.

[Pull what]

I seemed to remember the carb air off at 300 feet slipped in as a part of folk lore because it by passes the air filter and some schools did not want their engines digesting unfiltered air below 300 feet and on the runway.

Always bare in mind that if you kill your student the prosecution barrister will stand up in court with the official document from the manufacterer or CAA to try and prove your negligence.If you are operating the aircraft outside these parameters or instructions as well as joining BUPA, I suggest your make sure you major assets are put in someones else name.