- Location: Knoxville, Tennessee
- Accident Number: ERA24FA176
- Date & Time: April 12, 2024, 16:33 Local
- Registration: N9236J
- Aircraft: Piper PA-32R-301
- Aircraft Damage: Destroyed
- Defining Event: Structural icing
- Injuries: 1 Fatal
- Flight Conducted Under: Part 91: General aviation - Personal
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On April 12, 2024, about 1633 eastern daylight time, a Piper PA-32R-301, N9236J, was substantially damaged when it was involved in an accident near Knoxville, Tennessee. The commercial pilot was fatally injured. The flight was operated under Title 14 Code of Federal Regulations Part 91 as a personal flight.
The pilot departed on an instrument flight rules cross-country flight. About 15 minutes after departure, shortly after reaching a cruise altitude of 8,000 ft mean sea level (msl), the pilot reported to air traffic control that he was “picking up moisture in the clouds” and asked for a course deviation or a higher altitude. The controller approved course deviations and cleared the pilot to climb to 10,000 ft msl, which the pilot accepted. A performance study of the airplane's ADS-B flight track data showed that the airplane's airspeed decreased during the subsequent climb, and the airplane reached a maximum altitude about 8,500 ft msl and a minimum airspeed around 80 knots (kts) before it rapidly rolled left and lost altitude at a rate of about 1,300 ft per minute, consistent with an aerodynamic stall. The airplane briefly leveled off before entering a descending right turn, reaching a descent rate of 6,000 ft per minute. The descending turn continued until flight track data was lost at an altitude about 5,750 ft msl. At this time, the airplane's calculated calibrated airspeed was about 210 kts; the airplane's published never-exceed speed (Vne) was 197 kts indicated airspeed.
A witness on the ground near the accident site observed the airplane “twirling” as it descended below the clouds and also observed debris falling from the sky. The wreckage was distributed over a distance of more than 10,000 ft, consistent with an in-flight breakup. Postaccident examination of the airplane and engine revealed no evidence of a mechanical failure that would have precluded normal operation. Control cable separations and airframe structural fractures all exhibited characteristics consistent with overload failure. The airplane was not equipped with anti- or de-icing equipment and was not certified for flight into known icing conditions.
Review of weather information for the area indicated cloud bases around 4,500 to 5,000 ft with tops around 18,500 ft. The freezing level was around 5,500 ft, with supercooled large droplets (SLD) likely between 6,000 and 8,000 ft. The pilot filed his instrument flight plan for the accident flight with a flight planning application that generated a route briefing. The briefing contained weather information for the route of flight, including the forecast for moderate icing conditions; however, information regarding the potential SLD conditions would have been contained in supplemental icing information not provided in the standard briefing. Whether the pilot accessed supplemental icing information before the flight could not be determined.
Flight track information indicated that the airplane likely entered instrument meteorological and icing conditions shortly after takeoff, and that the airframe and flight control surfaces began to accumulate ice rapidly, as the time between the pilot's request for a higher altitude and the loss of flight track data was about 2 minutes. The airplane then likely encountered an aerodynamic stall while flying at an airspeed of 80 kts (15 kts faster than its maximum published stall speed). This was consistent with the effects of increased drag and stall speed due to ice accretion. It is likely that the pilot lost control of the airplane following the initial aerodynamic stall and was unable to recover. During the subsequent descending turn, the airplane exceeded its structural limitations, resulting in an in-flight breakup.
The pilot held an instrument rating; however, review of available logbook information indicated limited recent instrument experience, with two instrument approaches and one holding procedure conducted during an instructional flight about 7 months before the accident. Whether the pilot's loss of airplane control was the result of his inability to control the airplane due to ice accretion, a lack of proficiency in instrument flight, or a combination of those factors, could not be determined.
Although the pilot's awareness of the potential for SLD could not be determined, the route briefing generated at the time he filed the flight plan provided adequate information to alert him to the potential for icing conditions along his intended route of flight. Nevertheless, the pilot chose to depart and continue into an area with a known potential for icing conditions in the airplane that was not equipped to do so.
- Probable Cause: The pilot's decision to depart into an area of instrument meteorological and icing conditions, which resulted in loss of airplane control and a subsequent in-flight breakup.
