On April 25, 2021, about 1103 eastern daylight time, an experimental, amateur-built Kitfox Classic IV airplane, N90KF, was substantially damaged when it was involved in an accident near Mountain Rest, South Carolina. The pilot and passenger were seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, he departed Oconee County Regional Airport (CEU), Clemson, South Carolina, with his passenger for a local sightseeing flight during which they intended to survey fields that might serve as runways. They would descend to about 500 ft above ground level (agl) when they found a field to survey for length, power lines, and stumps, and then climb to 1,500 to 2,000 ft agl to fly to the next field. The pilot stated that the engine had been running smoothly during the 20-minute flight; however, after they surveyed the third field and began to climb out, the engine stopped producing power about 600 ft agl and the propeller continued to windmill.
The pilot selected a field for a forced landing, established the best glide speed, and turned on the electric fuel pump, which restored some power to the engine for about 10 seconds, but not sufficient power to maintain altitude. He stated that, when he realized that the airplane would not make it to the selected field, he brought the throttle to idle and performed a forced landing into the trees.
Examination of the wreckage by a Federal Aviation Administration (FAA) inspector revealed that the main wreckage came to rest upright in a creek in a nose-down attitude. The empennage was fractured and located in a tree and one wing was fractured and located about 50 ft from the main wreckage.
A postaccident examination of the engine and airframe did not reveal evidence of any mechanical failures or malfunctions that would have precluded normal operation. Compression and suction were achieved on all but one cylinder, which was impact damaged. Fuel recovered was light blue in color and absent of debris. The electric fuel pump was turned on and the engine subsequently started and operated without any observed anomalies. The engine was not equipped with carburetor heat.
At 1054, the weather reported at CEU, about 17 miles southeast of the accident site, included a temperature of 64.4°F and a dew point of 53.6°F. The calculated relative humidity at this temperature and dewpoint was about 68%.
A High-Resolution Rapid Refresh (HRRR) model sounding was created for the accident time and location with a surface elevation of 1,676 ft mean sea level (msl). At an elevation of 2,207 ft msl, the HRRR sounding indicated the temperature was about 57°F and the dewpoint was about 45°F, with a relative humidity of 64%. Review of the icing probability chart contained within Federal Aviation Administration (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 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 percent, "…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 percent, or when visible moisture is present in the atmosphere."
According to the engine installation manual, "An air filter and carburettor heat (both not supplied) should be incorporated in the air intake ducting."
The airplane and engine were operated in the experimental airworthiness category, and as a result, there were no requirements to install carburetor heat.