Use of Carb Heat (merged)

[1279shp]

Here's an interesting one for all.

Use of carb heat during 'stall' training.

Does it matter carb heat OFF before recovery or after?

Recover + Power + Carb Heat
Recover + Carb Heat + Power

Realising training is @ FL030

@@

Also in a go-round situation during training, shud it be firewall throttle then/as carb heat OFF, or carb heat OFF then/as firewalling throttle.

Your thoughts/training/methods? :hmm:

[High Wing Drifter]

Always power first, that way you at least arrest/slow the descent as soon as possible. Then drag flap up (if down) because that has the next major effect that could prvent a good climb. Then carb heat cold to give you full power.

[NZLeardriver]

I was always taught carb heat off thru 65kts for stall training (so before stall really begins), and on finals (so usually before go around is decided) for the landing.

What makes this so urgent that you have to post it in 5 different forums?

[TheOddOne]

Also in a go-round situation during training, shud it be firewall throttle then/as carb heat OFF, or carb heat OFF then/as firewalling throttle.

In my view, carb heat should be selected to 'cold' on very short final, prior to the flare, so that you're ready for the go-around. There's enough to worry about in a go-around without one more distraction.

The term 'firewall' gives an impression to me of a sudden slamming of the throttle fully open. Normally aspirated engines should have the throttle advanced from idle to full power in not less than 2 seconds, to avoid a rich cut. I've witnessed an aircraft crash because of too-rapid application of power in a go-around and the subsequent rich cut.

Similar philosophy applies, I believe, in the application of power during stall recovery. You need full power ASAP. I think you get that by
a) selecting cold air
b) progressive application of power over 2 secs.

I think the above ought to be easily be accomplished whilst adjusting the attitude with the other hand.

Many a/c are placarded with a minimum time for throttle from idle to full power.

3,000' sounds a bit low for ab-initio stall training, even if you should be able to recover in a few hundred feet.

Cheers,
TheOddOne

[Groundloop]

I was always taught to put carb heat to cold before opening the throttle. My instructors said there had been cases of engines cutting out if throttled up quickly with carb heat on. Don't know if that is true but that is what I was taught.

The other solution, if throttle is next to carb heat, is as you open the throttle push the carb heat in with one of your fingers.

[Gargleblaster]

Hmm, sorry, I don't think these questions are soo interesting for a lot of people in here, no offense, but this is "kindergarten stuff", although I see from your profile that you have an ATPL and that you are a pilot ?

In stall training, you turn carb heat off already when approaching the stall, typically when airspeed passes a given value depending on AC type. So when you apply full power in the recovery, the carb heat is already off.

When landing, you turn carb heat off just after turning on final. So when applying full power on goaround, carb heat is already off.

Generally in other situations, the rule is carb heat off, then full power.

[Ultralights]

part of my pre landing checks, carb heat Off!

[1279shp]

Thanks for the opinion, There's some debate amongst some of us bus drivers and airline CFI's over a current 'required teaching' from the authority. Simply wanted to gauge opinion/get thoughts.

Back to skool don't hurt anyone!

[plumponpies]

My understanding: Carb heat-power-recover, that way with the carb heat off, you get the max rpm from the engine. Select carb heat off in anticipation of recovery 1-2sec before. Likewise on approach at about 200ft carb heat off to anticipate a go-around.

[Delta Wun-Wun]

I always teach a "300ft check" on final appraoch. That being 1. Carb Heat to cold. 2. Landing light checked on. 3. "Clearance" to land. 4. Runway is clear.
That way carb heat is cold in anticipation of the "go-around" and if the student later moves onto a more complex aircraft, they are used to doing a check at 300 ft which can be substituted for "Reds, Blues, Greens, Whites."

[ibaker]

part of my pre landing checks, carb heat Off!
- Joey! Carb Heat Off on pre landing checks, isn't it carb heat on when on base or final

[unfazed]

Sorry Gargleblaster but you are talking "Tosh"

I do not advise my students to set carb heat cold after turning finals - DISCUSS !

[Sunfish]

Muggins does carb heat on on descent. Carb Heat OFF is selected at three hunded feet or therabouts as I make a consciuos decsision that my approach is OK and I am proceeding to land.

Of Course i am a sinner, and have forgotten the thing before, but I try!

[Whirlybird]

When landing, you turn carb heat off just after turning on final. So when applying full power on goaround, carb heat is already off.

If you do that with a C150 with a continental engine, on a warm day with high humidity, you're chances of having engine failure are extremely high! I'm a helicopter instructor, not f/w...but I have a share in a C150 and I know about it. We're had carb ice starting to form (ie lowered RPM) on the ground before takeoff and in the cruise...so we'd certainly get it in the descent if we followed that sort of advice. Apart from the fact I follow the POH, which doesn't recommend what you're saying. I gather carb heat in or out on final depends on type of aircraft, which makes a lot of sense.

[DubTrub]

Gargleblaster When landing, you turn carb heat off just after turning on final Better not instruct in an 0-200 powered C150...or an 0-300 powered C172...or any small-Continental-powered Cub, Luscombe, Jodel, etc. It is not "kindergarten stuff" at all.

Too many instructors, themselves taught in C152/Tomahawk/Pa28 types with Lycomings, have never been taught the fundamental differences in construction between Continentals (up to the 0-300) and similar-sized Lycomings. Unfortunately, it is also not part of the PPL "Technical" ground school/exam either. Therefore this information is not passed on to new students, and more fundamentally, the difference in piloting technique required to prevent engine stoppage on power application if they find themselves piloting aircraft so equipped.

You beat me by a whisker, Whirly!

Edit Quite a good thread on the subject here (http://www.pprune.org/forums/showthread.php?s=&threadid=147839&highlight=carb+continental)

[Dixons Cider]

Landing in an Islander once, cold day with temp/dew point reasonably close ie lots of moisture in the air.....

...Short finals (maybe 150-200ft), carb heats off as normal....landed and realised is was a bit quiet as both props came to a stop on the landing roll!! Some funny looks from the punters as I cranked her up again and taxi'd off as if nothing had happened.

Good lesson

[J430]

The great carb heat debate!!!

Well when you apply the common sense approach from the constructive comments here, plus do some research into accidents in the circuit area that were most likely because of carby ice you view this differently.

Dixons Cider has a good point, in the right conditions with low or nil power set, ice can be quick.

I hold carby heat until over the fence, if i am busy with the landing i.e. crosswinds etc, forget the carby heat, if you land OK, if you decide to go around the plane will still perform better than that of a static ground roll even with the heat on. try it one day you will see the performance is not that bad, sure it is less, but not that much.

When you think about reducing power for decent, crosswind or where ever, pull the heat then pull the power, and leave it until you are sure you can complete the landing, then put it in. If its too busy, complete the landing and don't worry. If you need to go around the little lost will hardly be a problem. At least this gives better performance than the ice bucket you might have otherwise.

J

[Charlie Foxtrot India]

You could always read the POH and see what it says.

For example, you shouldn't firewall the throttle in a Tomahawk with the carby heat hot, you can get a lean cut as there is no accelerator pump. So I teach to check for ice on downwind and then leave well alone (as per POH)

Just another point, it's been a long time since I had the pleasure of flying an Islander, (I no longer have that kind of upper body strength.....) but I could have sworn it was fuel injected........?

[homeguard]

Well it must be type dependant or be directly relative to the purpose of the excersize.

We teach, apply the Carb Heat on Base Leg prior to reducing power and set cold at 300ft prior to landing or 'touch and go' together with a speed check, runway clear etc. On stall training the students learns to apply heat at the time of applying power for the recovery simply because we believe thay should have that skill in the event a recovery is ever undertaken in anger at low level, during the approach, when heat will be applied, without getting finger tied.

When hot air is applied the fuel mixture is enriched and therefore the use of heat must be related to the fact that it could lead to a rich cut due to plug fowling. A balance needs to be drawn. The Continental is prone to icing more than the Lycoming but the Lycoming is more prone to running rich.

This cannot be a silly question that has been raised. Thank you for doing so.

[Chimbu chuckles]

Ahhhh...carb heat...don't got it my Bonanza...but seem to remember arriving back at Narabri in the dark in VH-GIL. To put some context to GIL it was a fast back C150...Gilgandra Aeroclub's first all metal tariner...for you youngters...that's a mid 1950s C150:ok:

Well we,...one of my students (I was a 270 hr grade 2 1/2 Instructor...had travelled that morning to...ummm...oh yeah...Coonabarabran, with namoi Aeroclub Pres in his almost as ancient 172, to pick up this piece of crap 150...'cause my student, a Policemen from Mungandi, was thinking about buying said aviation device....well I think we got dropped off at Coooonabarabran at about 0700...that's in the morning:ooh:...and we fecked off in this Fastback 150 for a days sorta toooling around...ssee if he really wanted the fecking thing...and after tooling around a fairly huge section of SW QLD and NW NSW we arrived back at Narrabri...we had landed on some highway somewhere and filled the tanks at a road side servo...anyway...it ws fairly fecking dark...and winter time..so fairly fecking cold....and the engine stopped on finals so we landed...and pondered why we couldn't taxi...then I thought about carby ice..so we tried to start it and it did...so we taxed in and the CFI...Glen (Opps edit!) was his name....well he sorta shook his head in...dismay maybe?...as we fronted up to the bar for this really big pissup///sorta like tonight really....anyway all was forgiven by dawn 'cause this crop duster topped us with mo visible effeort upon his part...editted....even pished what followed..while true was inappropriate:E :ok: ..somethings best left in the memorybanks:ok:

[FlyingForFun]

Good points re the difference between Continental and Lycoming.

However, does it not make sense to teach students a technique which will work for the majority of engines? I teach my students to leave the carb heat on until either going around or after landing. As already mentioned, in some aircraft doing anything else is asking for an engine failure in the right conditions. But even if your engine is not prone to carb icing, teaching it this way will enable the student to go on and fly these Continental-powered aircraft without needing to change their technique.

Discuss.....

FFF
---------------

[tutu]

Fully agree with J430. Been in light aviation as an instructor for 35 years. had all sorts of carb icing including a cut at full throttle climbing out of Wellington in a 172.
Many stopped prop landings in early days because we were taught to put carb heat off at 300ft or on final.. Now it stays on until I cross the fence or after landing.
As for stalls what would you do in an emergency? Start groping for the carb heat knob instead of hitting the throttle?
To keep the FTO's happy I put the carb heat cold approaching the stall but personally go power first and get the aircraft climbing than worry about fiinding another 100rpm.

[Dixons Cider]

Gday Charlie fox

there are many different models of the venerable BN2 my man, and sadly ours were not injected - for some reason that 260 horse Lyc was quite prone to a bit of ice, updraught carbs or something...

Agree with tutu and others - stall situation, get the power coming up, fly the aeroplane, then fine tune things. Prioritise.

[Whirlybird]

FFF,

What you say makes sense. However, while teaching it, why not point out the reasons, and the fact that different types require different treatment, and that different engines are different, and that when flying a new type you should read the POH first and go by that.

As a student, I was never told any of the above. I was told to leave the carb heat on all the way down as it happens. Later on, another instructor said I should push it in on short final. Explanations for both techniques made sense to me. What made less sense was why each egotistical instructor insisted it was done his way, that this was right, and no other way was. What made even less sense, and IMHO is downright dangerous, is that no-one mentioned that it could depend on the aircraft or engine type. I suspect they didn't even know!!!

Students aren't stupid. You can tell them to do something, while pointing out that this may not be the way they should do it now and for evermore, not matter what.

This isn't kindergarten stuff. It's basic, yes, but a lot of it is badly taught at times, and frequently misunderstood. More discussion of it can only be to the good. :ok:

[fokkerking!]

Carb heat off in the before stall checklist, with carb heat on it won't give you full pwr to recover, and in the short period in which you do the stall practise you won't get ice build-up (unless you are flying a pa32-260 that builds ice within a few minutes even when its 20 degrees outside!). On short final I normally put the carb heat off at 200 feet or something, again depending on type and conditions. But it should always be off when making a go-around, especially on hot humid days!
just my 2 cents............

[LocoDriver]

Industry standard(aero club/flying school) is carb heat off at around 60kts prior to stall recovery.

On approach, should be on prior to reducing power for approach, LEAVE IT ON when on finals, untill you are CERTAIN of making the runway in a full glide situation. IE just prior to crossing the fence.

Carb heat is there to be used.


Cheers!
:ok:

[foxmoth]

What made less sense was why each egotistical instructor insisted it was done his way, that this was right, and no other way was.

You do find this with some schools/instructors, in any one school it should be taught the same by all instructors, though on a checkout they should be looking more at "is it safe" rather than just is that how I teach it.

[DFC]

with carb heat on it won't give you full pwr to recover

Perhaps we need to remember that the recovery from the stall is made by reducing the angle of attack.......i.e. usually moving the stick forward.

Adding power is used to minimise the height loss.

Taking that in mind and the worst case scenario of a stall at low level one has to think about what actions are required after the stick is moved forward.

The most deadly stall/spin position is the old base to final turn. Usually at a height where even those that put the carb heat to cold on short final have hot air selected.

Thus the stall should be entered with the carb heat hot air on so that the student can practice all of the actions required to be completed in the worst case scenario.

Regards,

DFC

[McD]

1279shp, check your PMs.

McD

[Sunfish]

I confess to having had the engine go silent on a 150 after lining up. Pushed the throttle in too fast. Embarrasing to have to tell the tower, but it started first try and I was more careful afterwards.

C150's will ice if you look at them wrong. Carb heat goes on just before I throttle back and reconfigure for landing. It stays on till about 300-250 feet which is when I take a decision that my approach is good enough to land. - that is if I remember it!

[1McLay]

1279shp

What is this "required teaching" from the authority?

It would be interesting to see what silly idea they have thought up this time and how it compares to everyones responses.

1M

[Whirlybird]

Sunfish,


I confess to having had the engine go silent on a 150 after lining up. Pushed the throttle in too fast. Embarrasing to have to tell the tower, but it started first try and I was more careful afterwards.


I've had something similar. I had to wait quite a while to backtrack, and suddenly the engine died. I taxied back to find out what was wrong, and got a very, very informative impromptu lecture on the differences between Continental and Lycoming engines.

After that I started leaving the carb heat on until I'd lined up. The problem with that is, sometimes I forgot to push it in. Not that it seemed to matter much in the C150 with one person; we just climbed a little more slowly, that's all. But I now have a new routine before take-off - after power checks, carb heat out, then pre-take off checks, then carb heat in. Then just give it a short blast of carb heat prior to lining up; I won't forget it, since it hasn't then been on long.

One thing's for sure; since I started flying the C150, I'm a lot more aware of RPM, how the engine sounds, and noting immediately if all just doesn't feel quite right. Which can only be to the good, of course. But I can't help wondering if the higher accident rate for the C150 over the C152 isn't due to pilots transferring from one to the other without knowing all of the above. :(

[1279shp]

Whats being recommended is in stall training:

Carb Heat away, then power.

In real life though, which is why we spend so much time training, my argument is that habitual 'carb heat then power' may not be best at all.
Okay at altitude prob no great probs which goes first but low on a short final, different story.

NZ is mostly a Cessna equipped country, putting 'both to the firewall' almost simulatneously is easy but in other types not so.
Hence if we train something one way, when the time really comes, faffing about to stow heat could/would become the 'automatic' priority, and in a non-Cessna that could be dangerous. Wudn't you rather you rather be pushing for some go-forward first, rather than trying to get rid of a bit of heated air in the front end?

The loss of 3 or 4 % of rpm when full power is requested with Carb Heat ON, is hardly going to be noticed for a few seconds is it?
:ooh:

[1McLay]

Damn Straight 1279shp

spose its the same argument of teching recovery at onset or recovery at the stall.

I think both of them are nescesary, but for a habitual process you want pilots to recognise early or recover automatically before the thing stalls.


keep ya powder dry


1M

PS. What dus it matter to you...dont you drive a turbine? :p

[Ultralights]

funny thing is, in my training many moons ago, i was taught to use carby heat when needed only, as constant use can increase the risk of detonation, i was taught in Piper warriors, archers and arrows. i have only ever suffered a bout of carby ice on a long descent during a nav on about a 15 deg day after fog lifting- high humidity.

I will only use carby heat without evidence of icing on long descents in raining or very humid conditions.

There has only been 1 time i have had an engine stop on mid final, i set up the approach, pulled power to idle, and the prop stopped, i was flying a Jabiru at the time. i landed normally and rolled to a stop on the taxiway, after a quick check of the essentials, fuel good, no fire etc, i restarted with some difficulty, and taxied back to the hanger, first assumptions were carby ice, and not to worry about it, but i still removed the cowl, and found that the idle position throttle stop on the carby had broken off, allowing the throttle to close completly.

I would be curious to know why different techniques are used!

[High Wing Drifter]

Just to add a couple of things:

The current training guidance (so I'm told) is to set CH hot on downwind and then set back to cold on final. This thinking is based on the assumption that for CH to be effective, the engine must inducting (revving) to a greater degree. CH with an idling engine is not very effective (so the CAA say).

The discussion thus far seems to be centre on responding to training drills where you know when you are going to go around. The reality is that the need to go-around can be extremely sudden and unexpected. For me it is power, then drag flap, then CH cold. At the very worst I slow the rate of descent immediately.

I have never heard an engine cough and splutter because of CH, only because the power is applied too suddenly regardless of CH setting.

[A37575]

In the Cessna 150/52/172 series, carb heat should be left on until after landing. During a go-around if the carb heat has been previously on during final approach (which it normally will be) the throttle should be opened to full power first, followed by carb heat to off. Makes sense, as the full throttle with carb heat on ensures that hot air dissipates any previous ice build up thus ensuring full power. Carb Ice can build up amazingly quickly with low power and carb heat cold under certain atmospheric conditions.

Read the Cessna 172 manfacturer's POH which states quite clearly: "Baulked Landing - Throttle wide open - Carburetor Heat - cold. Similarly: "After Landing - Wing flaps up - Carburetor Heat - Cold.

For a touch and go you should apply full throttle first - followed by carb heat to cold - same as for go-around procedure.

The aircraft and engine manufacturer would not recommend these procedures unless they had been thoroughly researched and in any case these procedures form part of the certification program.

My advice? You can't go wrong if you stick to the manufacturer's advice. If you think the manufacturer is wrong, then conduct your own measured trials and give the manufacturer the benefit of your expert advice. I am sure it would be greatly appreciated.

[McD]

Hmmm... I guess I'll have to try this again....

1279shp, please click HERE (http://www.pprune.org/forums/private.php?s=)

[Dick Whittingham]

High Wing Drifter

I have had a near refusal of an engine to run on carb heat "on", but it was in extreme circumstances, on a a Harvard, P&W 1340 cubes, 650 odd bhp, OAT about 35deg, field 4000ft amsl.

This was at the end of a simulated forced landing, and on opening up the engine just coughed and spluttered until the carb heat went back to cold. And, no, it was not caused by too rapid throttle opening.

I have also heard of a case of an aircraft having engine cut-out on takeoff following carb icing on a long taxy out.

Moral. Most of the time everthing is OK. Just now and then you get bitten.

Regards, Dick W

[High Wing Drifter]

I have had a near refusal of an engine to run on carb heat "on", but it was in extreme circumstances, on a a Harvard, P&W 1340 cubes, 650 odd bhp, OAT about 35deg, field 4000ft amsl.
Yes, I would imagine problems at a density altitude of 7000' and with 150 celcius in the carb throat. Use of the primer would probably weaken the mixture!
:uhoh: (I jest of course) :D

I have also heard of a case of an aircraft having engine cut-out on takeoff following carb icing on a long taxy out.
I'm not suprised at that. Even considering my meagre experience I have seen icing when taxing on numerous occasions.


Moral. Most of the time everthing is OK. Just now and then you get bitten.
I'm sure. I guess there should be a midicum of flexibility to deal with the exceptions (like the one above).

[effortless]

Warrior carb heat off below 500 on final. Same on 152 at the club I use.

[Whirlybird]

My advice? You can't go wrong if you stick to the manufacturer's advice.

Excellent advice. :ok: I'm amazed how few people take it...and that sometimes includes instructors! Have you ever tried to ask to read the POH at some flying clubs - they look at you like you've gone completely insane. :eek: :confused: Not all aircraft and engines are the same, and the manufacturers do actually know about them.

[High Wing Drifter]

Manufacturers advice is good where it exists. Flight manuals aren't always that specific and some probably contradict the latest CAA training guidance.

[unfazed]

Whirlybird - Piper PA28 POH states that carb heat is NOT required when reducing power for approach (situated within hot area of engine bay). I pointed this out to my instructor at the time who was adamant that carb heat should be used as a matter of course.

I believe the instructor was right, why not put carb ht on? It is good practice for most aircraft and will not cause problems, unlike getting used to no carb ht then switching back to Cessna and encountering a problem.

[Genghis the Engineer]

I 99½% agree with Whirlybird, and in particular I do rant regularly about clubs (and even sometimes syndicates) who seem to regard the POH as a "classified document" only to be seen by a chosen few.

It is probably the best argument in favour of the US rule that the POH must be kept in the aeroplane - at-least then you've got a fighting chance of getting at, and reading, the thing. But even there I've had instructors who paid lip-service to the POH and did their own (not always astoundingly safe) thing !


But, it's worth remembering that whilst he or she may well have been the cleverest person ever to fly the aeroplane, the company test pilot probably only did a few hundred hours on the type before signing off the POH and going onto the next project. There may be instructors or pilots out there with many thousands of hours on type.

So, whilst I agree that you are highly unlikely to go wrong in following the manufacturer's advice, it is possible that somebody later will find a *better* way of doing something. But, before taking that on board, think hard.


And I have to confess that I hadn't previously noticed (I've just looked it up) that the PA28-161 POH says you should not apply carb heat on approach unless there is an indication of icing. I shall kick myself up the backside for not noticing that before, and change the way I fly it!

G

[Ultralights]

Read the Cessna 172 manfacturer's POH which states quite clearly: "Baulked Landing - Throttle wide open - Carburetor Heat - cold. Similarly: "After Landing - Wing flaps up - Carburetor Heat - Cold.

But that doesnt mean the CH must be HOT before go-around or after landing! i read it as check that Ch is Cold! if heat has been used.

does the POH indicate that CH must be HOT before or anytime while in the circuit or approach?

[jamestkirk]

It's a little radical but i always say that

'carb heat helps to prevent carb ice'

If anyone needs any furhter coaching on this subject, please do not hesitate to contact me.

Regards

[A37575]

Ultralight. Sorry -I should have added the earlier check that is in the POH and that was: Before Landing. Seats, belts, harnesses..secure. Fuel selector valve..Both, Mixture...rich. Carburetor heat..On (apply full heat before reducing power).

Thus if a GA is conducted the carb heat is already on, and is therefore taken off after full throttle is applied.

Also interesting to note that the POH (C172)states "seats secure" as part of the before landing drills. It is rare to see that in flying school checklists.

Also note that the POH does not state "gear down and locked" - for the obvious reason.

Yet certainly in Australia there is a universal myth perpetuated by just about every flying training organisation, that in fixed gear types the pilot should still mumble gear down and locked, to prepare him for the great day when he will step into a retractable gear type.

These flying schools seem to forget that before flying a retractable gear type in command, the pilot must have undergone a Special Designs features course and have this annotated on his licence.

Whoops! I got off the original subject of carb heat use.

[unfazed]

Ghengis the engineer

As you are the chief Prune engineer perhaps somebody else should kick you up the ar?$e

Also don't forget that you can always buy your own POH from the manufacturer (I did and it was money well spent), yes I know it will be generic but even so it will save you a lot of time and wasted effort.

[ShyTorque]

The manufacturer's POH should always be used as the authoritative document if there is seen to be conflicting advice given from other sources.

Ignore it and risk invalidating your insurance...

In the unfortunate event of an accident the CAA will step back and so will the training organisation, despite what one of their employees (FI) reputedly told you some time ago.

Say no more. ;)

[Genghis the Engineer]

Ghengis the engineer

As you are the chief Prune engineer perhaps somebody else should kick you up the ar?$e

Also don't forget that you can always buy your own POH from the manufacturer (I did and it was money well spent), yes I know it will be generic but even so it will save you a lot of time and wasted effort.


Please feel free, I teach a martial arts class every monday night and all comers are welcome.

In the meantime, I do own an original POH - and had read it several times, which is why I was particularly embarrassed to note that I'd missed this rather significant point.

If you wish I could pretend that I knew this all along and with my fingers crossed behind my back pretend some false superiority to everbody else (i.e., lie!), but on the whole I prefer to admit when I've screwed up - it hurts less in the long run.

G

[egbt]

Following the POH would seem to be the thing to do - if only Instructors and examiners would do the same! :confused:

Example from my experience:

Instructor:

Leave hot till on the ground (with a warning to avoid a rich cut by always advance throttle steadily and not ram it forward)

Skills test:

Change to cold c 300 ft for additional power on a go round.

1st revalidation (newish instructor):

Change to cold not below 500ft

Personally I do as J430 and turn to cold over the fence unless busy (or high on approach) in which case I leave it. If a little low at the fence and the carb heat is easy to hand as in the T67 I’ll go to cold a little earlier for a little extra power, killing 2 birds with one stone.

[unfazed]

"99½% agree with Whirlybird, and in particular I do rant regularly about clubs (and even sometimes syndicates) who seem to regard the POH as a "classified document" only to be seen by a chosen few"

Ghenghis - If you have a POH why do you rant regularily ?

Don't take it so personally that you missed the point re carb heat recommendations on PA28 - You are in good company as from my experience I have not met that many pilot's who appreciate that important fact

Mondays are not good for me so just carry on and Kick your own arse !

:p