According to the pilot, after his preflight inspection he started up the Cessna 172 and taxied to Runway 14 at Winchester Regional Airport (KOKV) in Virginia for departure. He performed a magneto check and noted no anomalies.
After waiting for three other airplanes to land and another airplane to depart, he took off around 1330.
Shortly after departing, he felt as if the airplane wasn’t climbing as well as he thought it should. Being too far away from the departure airport, he located a field for a possible emergency landing.
He executed a mental emergency checklist as the airplane descended and the engine continued to lose rpm. Around 1,700 feet, the engine stopped running completely.
The pilot attempted to troubleshoot by ensuring that the fuel selector was on both tanks, the magnetos were on, the mixture was rich, and he turned on the carburetor heat. He then primed the engine and attempted to restart it.
The engine started but was running roughly.
The pilot left the carburetor heat on and then turned back toward the departure airport.
The airplane would not climb with the available power and then the engine lost total power.
The pilot established a best glide speed and guided the airplane toward a field for a forced landing. During the landing, the nose landing gear separated, and the airplane nosed over. The pilot sustained minor injuries in the crash.
Following the accident, the pilot told investigators that he felt the loss of engine power was due to the formation of carburetor ice.
Examination of photos taken of the airplane following the accident showed that the vertical stabilizer and both wings were substantially damaged.
An FAA inspector examined the airplane and engine after it was recovered from the accident site. The inspector found that the carburetor float bowl contained fuel and that the intake was impacted with dirt from the accident site. After cleaning out the dirt from the intake, the inspector performed a successful test run of the engine and noted no anomalies.
At 1415, the weather conditions at KOKV, about 9 miles east of the accident site, included a temperature of 17°C and a dew point 01°C. Review of the icing probability chart contained within FAA Special Airworthiness Information Bulletin CE-09-35 revealed that the atmospheric conditions at the time of the accident were conducive to the formation of carburetor icing at glide and cruise engine power settings.
According to FAA Advisory Circular 20-113, “To prevent accident 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%, “…apply carburetor heat briefly immediately before takeoff, particularly with float type carburetors, to remove any ice which may have been accumulated during taxi and runup.”
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: The pilot’s delayed use of carburetor heat, which resulted in carburetor icing and a subsequent total loss of engine power.
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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.
17 C with a dew point of 1C is 33% RH. I really don’t see how carb icing could be the problem.
The amount of wiring, sensors, actuators and maintenance required to move a flapper valve to port hot air from the heat muff to the carb would be insane, not to mention when it failed you’d be back to pulling or pushing a cable to control the carb heat. Keep an eye on your gauges, follow the checklist and know the flight conditions. But what do I know, I’m just a mechanic.
I don’t understand why this vital function can’t be automatically turned-on and shut-off by monitoring temp and humidity. The need for pilots to do it manually is akin to stick shift transmissions — a vestige of a long-bygone era.
Remember that this is a 1961 certified aircraft…. no mods without FAA approval.
The Carb temperature gauge was an option with the MS carb used, so it could be added by an A&P .
I have one in my 1961 Cessna 175B and I can keep the carb temp above 32 degF with partial application, and only a little power loss.
The pilot
BTW, ‘stick shift’ transmissions are alive and well.
A lot of the so-called automatic transmissions are actually electronically shifted manual trans…..ie; twin clutch units…. for people who can’t count from 1 to 5 [ or 6 ].
just say’in…
Ditto 😉
In a carburetor engine the first thing to check is carburetor heat while the engine is still hot. Poor instruction leads to poor results. In the old days many airplanes had carb heat temp gages. Good idea to have one. I find most pilots don’t understand the use of carb heat. Every year this happens to someone. Very say.
Thanks so much for the report