Use of carb heat
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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
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
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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...
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...
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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!
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!
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SI 1148C - Lycoming engines with float type carburettors
"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.
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.
Last edited by rhwheeler; 22nd Jul 2011 at 11:49.
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I don't know of an airport with FLWOP as an identifier. I presume it's in a humid temperate place?
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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
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
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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.
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.
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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
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
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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.
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.
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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
.
Thats an ambiguous statement that needs qualifying.
I cannot quite agree with the way you phrased that, quote
Icing can occur at any phase,
Thats an ambiguous statement that needs qualifying.
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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??
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??
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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
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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?? 
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 ......
So my question is where did this procedure come from, the CAA, a big flying school, a text book ......
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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.
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.
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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.
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.
