Use of carb heat
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Use of carb heat
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.
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.
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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.
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Plus on final approach the student needs to be focussing on more important things than carb ht.
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
How does this risk go away in the final 2-300' of an approach?
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.
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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?
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?
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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.
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.
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Originally Posted by whopity
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.
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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
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When to put carb. heat cold/off
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.
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.
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Originally Posted by Cows getting bigger
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?
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.
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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?
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?
Moderator
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.
To comply with this we apply carby heat on downwind and make sure there is no icing then leave it cold on the approach.
To comply with this we apply carby heat on downwind and make sure there is no icing then leave it cold on the approach.
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.
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.
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
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
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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. 
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!
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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.
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.