N1720BBoeing B75N1

On July 28, 2021, about 0820 eastern daylight time, a Boeing B75N1, N1720B, was substantially damaged when it was involved in an accident near Lexington, Kentucky. The private pilot sustained minor injuries and the passenger was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

According to the pilot he departed with 46 gallons of fuel, after flying for 20 minutes, he was at 1,500 ft mean sea level when the airplane began to descend, and he was unable to maintain altitude. The pilot added full power, full mixture, and carburetor heat, but was still unable to maintain altitude. The pilot performed a forced landing to a private driveway. The airplane impacted a telephone pole just prior to touchdown.

According to the Federal Aviation Administration (FAA) inspector who responded to the accident site, initial examination of the airplane revealed that the wings sustained substantial damage. All engine and flight controls functioned normally and were verified from the cockpit controls to their respective control surfaces. The magneto switch was jammed in the BOTH position. The inspector was able to manually rotate the propeller with no binding in the engine.

The engine was examined on the airframe at a salvage facility by an FAA inspector. The engine was prepped for a field test run and fuel was plumbed into the engine, it started after a few tries, and then ran smoothly with no anomalies noted.

At 0854, the weather reported at Blue Grass Airport (LEX), about 11 miles northwest of the accident site, included a temperature of 22°C and a dew point 19°C. The calculated relative humidity at this temperature and dewpoint was 83%. Review of the icing probability chart contained within Federal Aviation Administration Special Airworthiness Information Bulletin CE-09-35 revealed the atmospheric conditions at the time of the accident were "conducive to serious icing at glide [idle] 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."