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I experienced a loss of power on takeoff in my Taylorcraft on Veterans Day in 2023. I wrote about the accident for Air Facts and now the NTSB has published its Final Report. I am writing this follow-up article to bring the incident full circle and to hopefully raise awareness of the possibility of having carburetor ice buildup prior to your takeoff.
Overview of the NTSB Findings
“The wreckage was examined after recovery to a storage facility. The wing and main fuel tanks contained fuel and were uncompromised. Fuel drained from the tanks was clean and free of water or other contaminants. The carburetor bowl contained a small amount of particulate matter. The carburetor inlet screen was clear.
The engine was turned through manually by rotating the propeller. Compression and suction were noted on all four cylinders and valve action was correct. The magnetos produced spark to all leads when operated manually. The spark plugs were normal in color and wear when compared to a Champion inspection chart.
The carburetor was broken from the engine consistent with impact damage; however, the cockpit controls remained attached. The carburetor heat knob was found in the “off” position.
Examination of the fuel system and engine did not reveal evidence of a preexisting anomaly or failure that would have precluded normal operation.
The recorded temperature and dew point near the accident site was about 48 and 35 degrees, respectively. On a carburetor icing probability chart, those temperatures were in the “serious icing – cruise power” range.
While the pilot described checking the functionality of the carburetor heat before as part of his normal preflight checks, and leaving it on for “a little longer” than normal as a part of that process, given all available information, it is likely that the temperature of the carburetor dropped during the extended operation of the engine while on the ground, and that during takeoff, the carburetor accumulated ice to a point that resulted in the partial loss of engine power.”
The Taylorcraft accident.
Discussion of Carburetor Ice
As most everyone knows, our carburetors are susceptible to ice buildup due to the venturi affect of the air flowing through the carburetor. We were trained to check the operation of carburetor heat prior to takeoff, to apply carburetor heat during slow flight, descents, reduced power, etc.
But, how much do you really know about carburetor ice? How much do you remember of what you use to know about carburetor ice? Have you ever paid specific attention to the air temperature, humidity and temperature/dew point spread during your preflight weather briefing? Have you ever considered the possibility of carburetor ice forming prior to or during your takeoff?
I must admit that prior to my accident I did not consider carburetor icing to be much of a problem and didn’t pay much attention to the ambient conditions.
Carb Ice causes more accidents than you may think
NTSB Reports from 2000 to 2011, carburetor icing was a cause or factor in about 250 accidents, on average, causing or contributing to two fatal accidents per year.
The FAA found that between 1998 and 2007, there were 212 accidents attributed to carb icing with 13 fatalities.
A common theme among the accidents attributed to carb ice, was the pilot’s inability to recognize carb icing symptoms and the improper use of carburetor heat.
The Conditions for Carburetor Ice May Surprise You
We know carb ice happens, but when, and at what humidities and temperatures? It makes sense that carb ice can happen at high humidity—lots of moisture means lots of icing potential. But, according to the NTSB, it’s possible to pick up carb ice with relative humidity as low as 35% at glide power. The FAA’s chart shows that carb icing is possible from 10F to over 100F (-12C to 38C), with serious icing possible from 20F to over 90F. (-7C to 32C)
Preventing Ice is Much Better Than Fixing It
Preventing ice is your best bet to avoid becoming an NTSB statistic. Follow your airplane flight manual or operating handbook’s instructions and use your carburetor heat whenever icing is probable. Remember, you can even pick up ice when taxiing or idling on the ground. If ice is likely, run the carb heat for a few minutes prior to takeoff to make sure that the carburetor is clear.
Clearing Carb Ice may make the engine sound even worse
As carb heat melts the ice, water is sucked up into the cylinders. Water isn’t gasonline, and your engine will cough and rumble as it digests it. Imagine while being stressed and under pressure while attempting to fix an engine problem. You suspected carb ice is the culprit so you have applied the carb heat only to hear the engine run rougher than it was before you applied heat. But stay calm because that’s a great sound because you’re clearing the ice. Search the NTSB records and you’ll find lots of cases where pilots turned the carb heat off because they thought they were making the situation worse, only to become a glider after a few minutes.
From AOPA
While carb ice theoretically can form at any temperature and at humidity as low as 30%, the sweet spot for carb ice is between 50 and 70 degrees F, when the humidity is greater than 60%. The probability of carb ice is not only affected by temperature/humidity but by power settings. At lower power settings, the engine is running cooler, thus providing less ambient heat to the air passing through the system. Less complete fuel vaporization also plays a role in the increased risk of carb ice at low power.
Fuel type
What’s the tiger in your tank? If your aircraft is approved for automotive and you use it, you are more likely to experience carb ice than if you flew the same airplane with aviation fuel in the tanks.
Tips for using carb heat
Carb heat should be applied well before you reduce power. This preheats the carburetor and keeps ice from forming in the first place. If you apply carb heat when descending from altitude and in the landing pattern, you can push carb heat off on short final, so you won’t have to worry about it in the event of a go-around.
If you need to make a prolonged, low-power descent, “clear” the engine periodically by applying power, heating up the carb heat system, and burning out any ice that may have accumulated.
Carb heat should be applied during extended ground operations in high humidity.
While carb heat shouldn’t be used when actively taxiing because it’s unfiltered air that could suck in ground debris, carb heat should be considered when holding on the ramp for extended periods of time to ensure that you don’t develop carb ice on the ground before takeoff.
Finally, if applying carb heat results in loss of power, or even in significant “roughening” of the engine, you should immediately open the throttle and pull the mixture control out far enough to smooth out the engine. As the ice melts, restore the mixture gradually to the original position.
Be Aware of Typical Icing Conditions:
During your preflight briefing, pay attention to the air temperature, humidity and temperature/dew point spread. A quick way to determine whether the air is particularly humid is by looking at the dew point. This is the temperature at which water vapor turns into a liquid and condenses. Be aware of a small split (temperature/dew point spread) between the ambient air temperature and the dewpoint when checking the weather. If they are relatively close together, carburetor icing is much more likely.
If you suspect carb icing, particularly if you’re within the sweet spot for temperature and humidity, use carb heat.
- Carburetor Icing and My Taylorcraft Accident - October 28, 2024
- An accident in my Taylorcraft - December 20, 2023
- Ya gotta be able to see the air - November 28, 2022
Very good read , we can all learn from this post
New
Good article, important info.
Many years ago I was on a x-country in my C-150L (auto fuel), flying quite low over swampland to stay under a low overcast. It was Winter, temperature probably 35-40F, and humidity was way high. I’d just scanned the panel, which I was in the habit of doing frequently, and all appeared normal. Suddenly, something tingled my Spidey-senses, and I quickly glanced again and noticed the loss of about 100 RPM..! Without thinking about it, in almost one motion, I firewalled the throttle, went to full-rich, and pulled the carb heat. The engine coughed a time or two, then raced to full RPM. Major relief, because going down in that area would have been disaster. I kept the carb heat engaged until I was able to climb to a healthier altitude. Point of all this is the carb ice, while most often occurs after throttling back for landing, can happen at cruise power… and even, as the article demonstrates, in a full-power takeoff.
Carb icing starts when the engine starts; even before there is any heat to melt.
When there is fuel and airflow thru the carb Venturi the cooling starts.
I’ve never had a carb icing issue in my Citabria, and I ususlly only apply carb heat on the 45 or downwind, as the engine starts to run so rough. This article will make me more cautious about the potential to have carb icing. I always check carb heat during the run-up and try to remember to apply carb heat when taxiing!
Interesting you mention pushing in carb heat on short final. I was taught to do this for the reason you stated (full power available to go around) learning to fly in England (where carb ice is a seemingly ever present threat). Many instructors I’ve flown with in the US seem surprised by this but it makes a lot of sense. After all, one is unlikely to get carb ice forming in those last couple of hundred feet if it has been correctly applied as you were reducing power in the pattern.
GREAT information. Thanks for sharing. I wasn’t aware of how critical carb icing can be.
It’s not only the ingestion of melted ice that makes an engine with carb ice run rougher after applying carb heat. The engine is already running too rich due to air restriction – then pulling carb heat on makes it run even richer.