Accident Sequence
On June 21, 2021, at about 1615 central daylight time, an Ayres S2R-T34 airplane, registration N4328P, was involved in an accident near Leoti, Kansas. The commercial pilot sustained minor injuries, and the airplane sustained substantial damage. The aircraft was operating under Title 14 Code of Federal Regulations Part 137 as an aerial application flight.
The pilot reported that the 510-gallon hopper was loaded with 10 ounces of FoamBuster Max, 62.5 gallons of Buccaneer 5 Extra herbicide, 300 gallons of Kugler KQ-XRN fertilizer, and 87.5 gallons of water, totaling 450 gallons of mixture. During the second spray pass, the pilot observed that the chemical mixture was foaming over and through the hopper vent. He climbed the airplane out of the pass and noticed foam emerging from the overflow vent. Looking forward, he saw the chemical reacting violently and emitting from the hopper lid. The windshield became fully obscured with foam, leaving the pilot unable to see outside the airplane. He opened the window in an attempt to determine his altitude, after which the airplane impacted terrain in a wings-level attitude. The airplane skidded on the terrain and came to rest upright.
Aircraft and Pilot Information
The airplane sustained substantial damage to both wings and the fuselage. A postaccident examination revealed no mechanical anomalies that would have precluded normal operation. The pilot reported that he had recently replaced the hopper lid seal but could not recall the exact date.
Chemical Compatibility
A jar test of the chemical mixture in the hopper was not performed by the pilot or ground loading personnel. The Kugler KQ-XRN technical sheet precautions stated, in part, “Use caution when mixing KQ-XRN with phosphate, sulfur, humic acid and products containing glyphosate, a chemical foaming reaction may occur. Kugler recommends always performing a simple jar test when mixing KQ-XRN with any pesticides and fertilizers.” According to the Buccaneer 5 Extra active ingredients, the herbicide contains 53.8% glyphosate.