Incident Overview
On July 28, 2021, at approximately 0820 eastern daylight time, a Boeing B75N1 (registration N1720B) was substantially damaged in an accident near Lexington, Kentucky. The private pilot sustained minor injuries, while the passenger was not injured. The flight was conducted as a personal flight under Title 14 Code of Federal Regulations Part 91.
Pilot Account
According to the pilot, the airplane departed with 46 gallons of fuel. After about 20 minutes of flight, while at 1,500 ft mean sea level, the airplane began to descend and could not maintain altitude. The pilot applied full power, full mixture, and carburetor heat, but the descent continued. A forced landing was executed to a private driveway, and the airplane struck a telephone pole just before touchdown.
Post-Accident Examination
An Federal Aviation Administration (FAA) inspector examined the accident site. The wings sustained substantial damage. All engine and flight controls functioned normally, with control continuity verified from the cockpit to the control surfaces. The magneto switch was jammed in the BOTH position. Manual rotation of the propeller showed no binding in the engine. The engine was later examined at a salvage facility; after being prepared for a test run and connected to a fuel supply, it started after several attempts and ran smoothly with no anomalies.
Weather Conditions
At 0854, the weather at Blue Grass Airport (LEX), about 11 miles northwest of the accident site, reported a temperature of 22°C and a dew point of 19°C, yielding a relative humidity of 83%. Review of the icing probability chart in FAA Special Airworthiness Information Bulletin CE-09-35 indicated that the atmospheric conditions were "conducive to serious icing at glide [idle] power."
Advisory Circular Guidance
FAA Advisory Circular 20-113 provides recommendations for preventing induction system icing. It advises pilots to use carburetor heat regularly under conditions conducive to atmospheric icing and to be alert for icing indications. When relative humidity exceeds 50%, the circular recommends applying carburetor heat briefly before takeoff, especially with float-type carburetors, to remove any ice accumulated during taxi and runup. It also stresses remaining alert for induction system icing during takeoff and climb-out when relative humidity is above 50% or visible moisture is present.