Question:

Prelude: An aircraft is flying straight and level. The MP & RPMS are constant. The outside air pressure, temperature, and moisture are constant. The mixture is set to best power. There is visible moisture in the air and dew point spread is (2) Celsius.

What is the first indication, of probable cause, of carburetor ice:

A) RPMs are erratic, redlining, over speed

B) Left wing drops

C) MP slowly drops 2" and airspeed deceased, EGT & CHT becomes cooler

D) Other

Had my first apparent run in with carb ice this summer flying from NH, back to NY with my wife. Flying straight & level, 2,400 RPM (In the 150 so no MP), sunny with a bit of haze, much bigger spread in the dew point/temp difference (Did look up temp/humidity on the graph and turns out we were smack dab in the middle of the chart for ice) leaned to best power. There was no warning what so ever. Instant 200 - 300 RPM drop for maybe 1 - 2 seconds, RPM's went back up, as I was reaching for the carb heat, it dropped again almost 300 RPM (All within 3 - 5 seconds). Pulled carb heat and everything went back to normal within 10 - 20 seconds. We were close to the strip where we get our maintenance done, so we landed there, checked the plane out and came to the carb ice conclusion.The interesting thing was we were right over a pass in the mt.s and it was the only place all day we picked up any air moving, Maybe that had something to do with conditions.

It's been an interesting summer, had a flap roller disintegrate with the flaps sticking at 20 practicing go-arounds into rising terrain (lesson learned), hit a hawk (Knocked the spinner off the 150, no other damage) and carb ice. So expenses for the summer were , new flap rollers, spinner and three pairs of undies.

Pete

During the time I owned my Ercoupe it iced up twice, both almost identical conditions. August, takeoff temps of mid 90"s on the ground, air temp of about 70 at cruise altitude with thunderstorms in the area. The only indication of any problem was a slow drop in RPM, from 2500 to about 2000-2100 over a few minutes, and a slow loss of altitude to go with it. No MP, EGT or much of anything else in the panel on that plane, engine was a C-85. The first time it was "what the hell is wrong, look for a place to land" until I pulled on the heat. The second time it was "this again, no problem".

If is it a Continental with a carburetor it will ice up. Temperature do not matter. They always ice up. I plan on it an use carb heat on both my 170b and 182. After take off I leave it on for a few minutes as insurance. Both have carb temp gauges and an frequent glances at the gauge to be sure it is in the green. Even my old pa 28-235 with an o-540 iced up frequently. Of course I live in the icing capital of the U.S. western Washington.

Ron

Guys,

Thank you for the information. It's a good review of real world encounters.

Stay safe and keep the venturi dry!

I tend to check carb heat often when I suspect carb ice. I think the seat cushion being sucked up my butt is noticed quickly when the engin runs rough. Had some this fall at 100 ft agl good thing I have a big cushion.
DENNY

I've gotten light carb ice a few times. I see it more of an increase in engine roughness. I haven't specifically noticed RPM drop though. Carb heat on for 10-15 seconds usually smooths things back out.

Often, the first indication of building carb ice is a decrease in manifold pressure. That said, many of the aircraft that are most susceptible to carb ice are not equipped with a MP instrument. And, in fact, hardly any pilot I know actually includes an MP instrument in his/her regular scan anyway.

Lycoming engines have intake runners routed through the oil sump, which conducts quite a bit of heat to the carburetor. As a result, Lycoming engines tend to be a LITTLE less inclined to make carb ice.

Continentals, on the other hand, have no comparable advantage, and in general tend to more readily make ice.

Having flown carbureted engines in Kodiak for eight years, including Lycoming, Continental and Pratt and Whitney engines, I have experienced some episodes of carb ice.

And, those varied, from a mild engine roughness as the first indication of problems to a full out total engine failure as the first indication. I can attest that those definitely get your attention.

The routine I adopted with most of these engines (the Pratts being the exception) was simple: I developed a routine of applying carb heat periodically at a regular interval.....whether I suspected carb ice or not.

The Beaver, equipped with a Pratt and Whitney R 985 engine, is equipped with a VERY effective carb heat system. So much so that pulling on full carb heat at cruise power will suggest to everyone aboard that an engine failure is imminent. But, the Beaver is equipped with a carb inlet temperature gauge, So the procedure recommended in the operating manual is, once cruise power is set, adjust carb heat on as much as needed to raise the carb temp to + 7 (or was it +4) Celcius, and maintain that inlet temp. Problem solved.

It's worth noting that many Cessna 180s came equipped with a carb air temperature gauge as well.......hint......

One thing worth mentioning is the certification standard for carb heat. The regulation for that requires that the certification specified temperature rise when carb heat is selected full "hot" must be met when the engine is at full throttle-i.e. : making lots of heat. Consider that when you NEED that heat most, the engine may in fact be making very little heat. And consider that the heat is coming from an exhaust manifold, which is constantly being cooled by cold outside air flow.

The point being that IF you do experience carb ice, it be hooves you to get that carb heat control to the hot position ASAP, in order to extract as much residual heat from that muff as possible.

Finally, carb ice often forms during taxi as you wait for the engine to warm on a cool day, or when held by ATC for traffic. I always apply carb heat and a bit of power as I roll out for takeoff to clear it out, then go to full throttle, followed shortly by carb heat to cold on the roll.

MTV

I was waiting for MTV to explain Lycomings. I flew all the 0-320s in various 172s and the 0-360 in the Cardinal on the pipeline in various midwest weather. No real cold like MTV up North. The only problems I had was rain or snow in cold air clogging the air filter. I never had any carb icing problems. I used carb heat only to give the engine unrestricted air. Once I experienced the problem, I kept the carb heat on allowing air into the carb through the hole in the bottom of the carb heat box below the butterfly. I kept the carb heat on until out of the weather. I couldn't operate in heavy rain or much snow because I needed good forward visibility to miss obstacles and terrain and to patrol my line.

MTV mentioned MP & RPM in the scan. I do look very closely at engine variables and make mental notes or write down the readings to contrast changes. Comes from debugging engines as an A&P.

Good write up MTV. Good guidance that may save my life and/or others.

I do not have a carburetor temperature gauge or OAT. That may change soon.

Everyone,

Thanks! Great guidance and solid information! Stay safe

A carburator temp gauge costs about $100.
Wouldnt that be a good instrument to scan and avoid ice?

Now can that instrument have a light so it turns on when icing conditionds in the carb are present?

motoadve wrote:A carburator temp gauge costs about $100.
Wouldnt that be a good instrument to scan and avoid ice?

Now can that instrument have a light so it turns on when icing conditionds in the carb are present?

I suppose that a light could be connected. But, generally the utility of that instrument is to simply adjust the carb inlet temperature with carb heat to remain above freezing. That requires partial carb heat, which in most aircraft means you are inducting unfiltered air into your engine, but as long as you only use this while airborne, that's not an issue.

MTV

My very first experience with carb icing was as a student in Anchorage, landing at Merrill Field. On very short final to 34, the 150's engine quit--the prop actually stopped. For a student, that was some event! Especially with half a dozen airplanes in the pattern, I felt about as big as the average mouse, but I couldn't just slink away and hide. I coasted far enough that I could pull near a taxiway and then push the airplane farther to clear the runway. Meanwhile, a couple airplanes were told to go around. When I got back in after pushing the airplane, it started immediately--the ice had melted in the interim. I had forgotten to pull the carb heat on before reducing power in the pattern.

My first experience with an aircraft with a carb temp gauge was the TR182 I was partnered in. It was a basic green/yellow/red gauge without actual temp indications, but it was useful. When I bought my current airplane, it had no carb temp gauge, but when I had the Insight G1 installed, I opted for the optional carb heat indicator, which is digital. I regularly look at it whenever I'm in visible moisture or when flying in high humidity even when I can't see moisture.

Since that first time at Merrill, I've had carb icing many times in a variety of airplanes, always at cruise power settings. In most cases, it was a loss of power that caught my attention; in a couple of cases, it was a rough running engine. In all of the cases, In every case, pulling the carb heat took care of it, sometimes with some more rough running before it cleared.

When my carb temp shows that carb icing could occur, I also pull the carb heat on periodically to clear out any that has formed.

Cary

Many people know but worth mentioning that if running with the carb heat on you can lean the mixture to compensate for the less dense incoming air. This will restore some of the lost power and reduce fouling of the plugs.

John Deakin explained me exactly how to run lean of peak using carb heat, and it worked.
Cool Cyl Temps 310s (usually are in the 360s) running at 9.2 or so GPH.

Only problem was it will go waay too slow 95kts to a 100kts or so at cruise.

Will start expermenting carb heat at cruise and leaning (rich of peak)

Question for you guys with carb temp gauges: What kind of gauge do you have and what temperatures do you see with carb heat on?

I used to fly a 182 with a Mid-Continent gauge that topped out at +30C. Pulling the carb heat would always peg the gauge.

On my O-360 I have a JPI EDM-700 with a carb temp probe. Full carb heat only increases the reported IAT by about 15F, which is not much! I put a thermocouple in the air box and measured the carb heat air at 180F, so I know the heater works. The IAT always agrees with the OAT with the airplane parked and cooled down.

I think the JPI probe doesn't just measure the carb air temperature, but the carburetor body temperature. The active element of the probe is staked into the threaded part and seems to make a pretty good thermal and electrical contact. At OSH a couple of years ago I asked the JPI guy about it and he agreed that the probe measures the carb body temperature, but I'm not 100% sure he really knew what I was talking about.

Anyone else with a JPI carb temp probe?

Thanks.

Had a good dose of carb ice today. I don't care who you are, it's a little spooky.

Thinking of buying this.
I see all Robinson helicopters have them.

Anyone tried it?

http://www.aircraftspruce.com/catalog/i ... etect2.php

mtv wrote:.....Lycoming engines have intake runners routed through the oil sump, which conducts quite a bit of heat to the carburetor. As a result, Lycoming engines tend to be a LITTLE less inclined to make carb ice. Continentals, on the other hand, have no comparable advantage, .....

The C-145/O-300 Continental has the intake routed through the sump, just like a 320, but in my experience they seem just about as probe to carb ice as the smaller 4-banger Continentals which have an intake spider.

motoadve wrote:Thinking of buying this.
I see all Robinson helicopters have them.

Anyone tried it?

http://www.aircraftspruce.com/catalog/i ... etect2.php

Respectfully, Robinson Helicopter Co does NOT use the above item. R22 and R44 helicopters are factory equipped with the Mid-Continent CAT system (formerly Richter Aerospace). Also, the temp probe location varies: the R44's CAT probe is positioned downstream of the butterfly which results in greater accuracy (RHC machined R44 carbs for this in the early 90's, until the carb manufacturer changed the design at their behest), while the R22's CAT probe is positioned upstream of the butterfly. Further, the CAT probe is installed within the carb bore so end of probe's threaded shank is flush within 0.015 inch. And don't over-torque the expensive CAT probe - 48 inch-pounds, max. Yes, carburetted helicopters are rather particular about their CAT setup...

More pilot info online at http://www.robinsonheli.com >Publications >R44 series >R44 Pilot's Handbook >Section 4 Normal Procedures >page 4-12, Use of Carburetor Heat.

Hover safely,
Pat