The student pilot, who was the owner of the Taylorcraft BC-65, departed Columbia Airport (KCUB) in South Carolina and was in cruise flight at an altitude of 2,000 feet mean seal level (msl) when the engine began to lose power “as if something was blocking fuel from getting to the engine.”
He applied carburetor heat “which was no help and only made for a greater loss of much needed rpms,” he told investigators.
The student pilot explained that he applied full carburetor heat but turned it back off about 30 seconds later when there was no improvement to the loss of engine rpm.
He added the engine eventually stopped producing power, and he made a forced landing to a road in a subdivision that was under construction.
The airplane sustained substantial damage to the left wing when it hit construction equipment during the landing roll. The pilot sustained minor injuries in the crash.
Examination of the airframe and engine revealed no mechanical malfunctions or anomalies that would have precluded normal operation.
The weather reported at KCUB, about 9.5 nautical miles northeast of the accident site, included a temperature of 55°F and a dew point of 36°F. The calculated relative humidity at this temperature and dew point was about 48%.
A high-resolution rapid refresh (HRRR) model sounding was created for the accident time and location with a surface elevation of 335 feet mean sea level (msl). At 1,752 feet msl, the HRRR sounding indicated a temperature of about 44°F, a dew point of about 33°F, and a relative humidity of 66%. At 2,351 feet msl, the HRRR sounding indicated a temperature of about 41°F, a dew point of about 33°F, and a relative humidity of 72%.
Review of the icing probability chart contained within FAA Special Airworthiness Information Bulletin (SAIB) CE-09-35 revealed the atmospheric conditions at those altitudes at the time of the accident were conducive to “serious icing at cruise power.”
According to FAA Advisory Circular 20-113, “to prevent accidents due to induction system icing, the pilot should regularly use [carburetor] heat under conditions known to be conducive to atmospheric icing and be alert at all times for indications of icing in the fuel system.”
The circular recommended that when operating in conditions where the relative humidity is greater than 50% and the temperature is below 70°F, the pilot should “apply carburetor heat briefly immediately before takeoff, particularly with float type carburetors, to remove any ice which may have been accumulated during taxi and run-up.”
It also stated, “Remain alert for indications of induction system icing during takeoff and climb-out, especially when the relative humidity is above 50%, or when visible moisture is present in the atmosphere.”
Probable Cause: A total loss of engine power due to carburetor icing, which resulted from the student pilot’s failure to use carburetor heat.
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This February 2021 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
There are very few times when carb heat cannot be used safely! Yes hot intake air will reduce power a small amount but only during extreme density altitudes will it actually cause serious reduction of power problems! Always use carb heat according to the pilot handbook! When in doubt apply carb heat before icing causes engine failure and leave it on until all doubt of carb icing has passed! Remember a “DEAD” engine will not generate any heat to melt ice in the carb!
This is one of those features of engine adjustment that should be fully automatic. These annoyances went away with the Model T ford. The automatic choke in car carbs eliminated the need for the manual choke, etc. Very primitive technology to require pilot awareness and operation of a carb heater. Sheesh!
I think we have a problem. This is what the NTSB printed report shows: “The pilot applied full carburetor heat but turned it back off as it resulted in a loss of engine rpm.”
This is the clarification statement by the pilot in addition to the above: “The student pilot explained that he applied full carburetor heat but turned it back off about 30 seconds later when there was no improvement to the loss of engine rpm.”
And then the report goes on to say this under “Findings” :
Intake anti-ice, deice – Not used/operated
So he did use carb heat, and 30 seconds may or may not be sufficient depending on conditions and aircraft.
Perhaps the findings would have been more correct in stating insufficient use of Carb heat?
Aren’t we glad that NTSB reports like this are “cross-examineable” if they are allowed to be presented at trial?
Part of the problem of dealing with carb ice is that the vast majority of flight students have never owned a vehicle with a carburetor – everything is fuel injection nowadays, with the exception of our airplanes. Carburetors might as well be alien technology, the concepts and theory of operation have to be explained to them carefully so they don’t get into trouble with ice.
I’ve also found that many (younger) CFIs don’t understand it either, so they can’t effectively teach it to their students. The best one was when a guy who claimed to be a 737-400 driver told me that jets don’t have carb ice problems, so why should GA aircraft? (That one left me shaking my head sadly.)
I don’t necessarily disagree with the finding, but it seems the NTSB gathered additional data that was not available to the general aviation pilot in determining probably cause.
In other words, don’t fly on excellent flying days….?
Great question!
But the answer is: You can ( and should) fly in those days, but check all the resources available in weather, including the ice formation risks and where expect to find them and in what situations and places. On the other hand, You must use the carburetor de-icing if You suspect ice in it and mantain that.