Use of Carby-heat

[class-e]

Hi everyone.
Alsthough this is my first post, I have watched and learned for some months now from you all.
My question to you all is this...

Some people teach that Carby heat should be used turning base on reduction of power, regardless of the weather conditions on the day. Whilst, in initial training, I have no problem with this, I think that in due course the student should be taught when Carby icing is likely to form and to use c-heat as required...not by habit!
Many of these instructors also teach that carby heat should be selected FULL COLD AFTER touchdown. When I was taught to fly, as a "late final" check, we would select carby heat to cold PRIOR to touchdown. To me this makes sense for a number of reasons....
(a) The lower you get to the ground, the more likely you are to pick up dirt etc. and do the pistons damage if you still have carby heat hot.

(b) The later a go-around is initiated, the more you want to have full power. The use of carby heat, as you all know, detracts from full performance.

So.......... when do you select Carby heat cold?

[Capt Homesick]

I like(d) to select carb air cold at about 400 feet on finals; the students liked the acronym CRA-P (Carb air cold, Runway clear, Approach path ok and Permission to Land). Exactly as you say, if I have to go around below that I want full power straight away, and I don't want to wreck the engine by ingesting dust or anything else.

[Charlie Foxtrot India]

I teach to "check for ice" as part of the downwind checks, and then leave it well alone.
ie Brakes, undercariage, mixture, fuel, carb heat hot, check for ice, hatches and harnesses, carb heat cold.
That stops the risk of people landing or trying to go around with it on hot, 'cos you're not going to get iced up between late downwind and landing.
Still there are many different ideas on this one, no absolute right or wrong way.

[BEagle]

Charlie Foxtrot India - that's what I teach. The risk of serious carb icing forming after completing the pre-landing checks is less important than the need to have full power available for a go-around!! And, Capt Homesick, no disrespect intended, I reckon that the idea of the late final acronym is a bit OTT. I note that it doesn't include a check of feet off brakes......?? The RAF used to teach some nonsense at the multi-engine AFTS of including "The 4 asymmetric checks" on final. These were 'Runway clear, gear down, stable approach, clearance to land'. What on earth was 'asymmetric' about these check items?? I once asked the CFS Canberra agent this - he couldn't explain!!

[This message has been edited by BEagle (edited 17 November 1999).]

[Wee Weasley Welshman]

Carb heat check operation on downwind. Select on during Base Leg. Turn off at under 500ft.

WWW

[climbs like a dog]

Depends on type, but if used then cold by 300'

BEagle
Those asymetric checks are like those I was taught at OATS when asymetric in the seneca where those critera had to be met before descending below asymetric committal height (300') due to a marginal go-around performance. Perhaps the same was true of the m/e AFTS type although surely not on ALL approaches. I mean if you lose an engine below 300' you're landing whatever happens.

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0 to 2000ft in 10 minutes

[puddlejumper]

I also favour the automatic selection of Carb Heat on the base leg as a precaution - but we also select it back to cold approaching 200' so that we are prepared for the go-around which is initiated if, at 200', the runway isn't clear, you are not happy with the approach, or landing clearance hasn't been given.

Just to go one stage further - I would like to enquire about the use of Carb Heat in the climb (apart from on the go-around where I agree you need all the power you can get). I teach, as I am sure most people do, that carb heat should not be selected hot when at full power as there is a detonation risk. However our Head of Training has recently suggested that this is a misconception and that because the Pilot Operating Handbook doesn't warn against this it doesn't necessarily apply. Anyone care to clear this up for me.

Cheers

PJ

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Your village called, their idiot is missing

[rolling circle]

puddlejumper, I suggest you point your Head of Training in the direction of the Engine Manual rather than the Pilot's Operating Handbook. I have not flown anything with a normally aspirated Continental engine for some time but I do know that every Lycoming manual contains a highlighted instruction not to apply carb heat at more than 75% power.

I heard of three incidents last year, one of which is in the latest AAIB Bulletin, of engines failing to respond after a descent with carb heat applied. Two of these aircraft ended up in fields. In each case the weather conditions were such that carb icing could be discounted (high temperature/low humidity). The common cause was that the engine 'rich cut' and, in these cases, it would have been better not to have applied carb heat which has the effect of richening the mixture.

It is always a mistake to do anything 'by numbers' in aviation. One should always operate the aircraft according to the conditions prevailing. Whilst it may be the case that a Continental engined Cessna always requires carb heat in the descent, the same is not true of a Lycoming engined PA28. The answer is to know and understand your aircraft and it's systems and to operate it in accordance with both the Pilot's Operating Handbook and the engine manufacturer's manual.

[BEagle]

Rolling C - I agree with you 100% on this!! I flew C150s with RR Continental years ago and was told by my instructors that the PA28 with a Lycoming engine was a totally different beast. Touch wood, I've never experienced carb icing in a PA28, but a poorly set up engine can suffer badly from the fouled plugs and over-richness which you describe. A response check/engine warm every 1000 ft in a prolonged glide - as for a PFL - is essential. But I've never bothered with anything more than a brief check of carb heat in the circuit - if conditions are so bad that a PA28 could suffer carb icing in the circuit, should you really be flying more than 1 circuit to land anyway??
RC - do you think one should bother with any 'final check' apart from 'Toes off, reds, blues, greens'?? I'd be interested in your opinion!!

[Capt Homesick]

BEagle, no offence taken, you may be right about a finals acronym being OTT. It worked ok (like I said, the students liked it and could remember it) but I'm all for learning a better way.
One other way of ensuring you put the carb heat off (in a C152 at least) is to tell the students ALWAYS to advance the throttle with their thumb stuck out at right angles- that way it catches the carb heat lever and pushes it in as well. That way fulll power WILL be available on the go-round (unless you've got the rich cut problem mentioned above, of course). Doesn't solve the dust ingestion problem, though.

[rolling circle]

BEagle, glad we agree about something. IMOH You cannot check too often that your aircraft is ready to make contact with the ground, I would not discourage anyone from doing as many 'Final' checks as they saw fit.

Personally, I check about three times on final approach that the gear is down and locked, even when I'm not flying a retractable! The only thing which makes one look more of a prat than landing with the wheels up is running out of petrol. There is a certain CAA FE who would vouch for that (twice!)

Capt Homesick, If you teach (on a C152) that your student should 'ALWAYS' advance the throttle with their thumb stuck out then, sure as eggs is eggs, one day they will do it in an aircraft where their thumb will contact the 'Gear Up' button. Never, ever, ever teach a student to 'ALWAYS' do anything. Teach your students to 'UNDERSTAND' their aeroplane and it's systems, whatever type it may be.

Many years ago a good friend of mine advanced the throttle with his left index finger 'stuck out'. He spread himself and his jet all over the airfield at Mona. Just before Christmas as well! I later watched him fly a Sea Jet the length of the main runway at Culdrose at 30 feet, inverted - Wow!

[BEagle]

RC - that FE wouldn't be 'Tips' C******d perchance??

[squeakmail]

Don't shout at me too loud, I'm asking for opinion.

Does anybody still refer to "downwind checks"?....as in "Check for ice on the downwind leg".

With so many base leg joins initiated by ATC isn't the current phrase "Pre-land checks" - just in case you don't get a downwind leg to trigger the action?

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LIVE in peace...or REST in it!

[rolling circle]

BEagle - You may think that, I could not possibly comment.

Squeakmail - Quite correct, the term 'downwind' checks is, and always has been, misleading in the commercial context.

[BEagle]

........or indeed elsewhere, Squeakmail. RC - I get your drift, mon brave!! Thought as much!!