Ayres Corporation S2R-T34 N4328P accident near Leoti, Kansas

Probable cause

The pilot’s loss of visibility in the cockpit due to foam created by the chemicals loaded in the hopper, which resulted in his inability to maintain airplane control during low-level flight and an impact with terrain. Contributing to the accident was the combining of chemicals known to produce foam and the pilot’s failure to perform a jar test before flight as recommended.

NTSB analysis

Before the aerial application flight, the 510-gallon hopper was loaded with 450 gallons of a chemical mixture. While on his second spray pass, the pilot noticed the chemical mixture was reacting and foaming over and out the hooper vent. He climbed the airplane out of his second pass and noticed chemical foaming out of the overflow vent. He looked forward and observed the chemical reacting violently, and it began to emit from the hopper lid. The windshield became fully obscured with foam, and the pilot was unable to see anything outside the airplane. The pilot opened the window in attempt to determine his altitude when the airplane impacted terrain in a wings-level attitude. The airplane skidded on the terrain and came to rest upright.

A postaccident examination of the airplane did not reveal any mechanical anomalies. A jar test of the chemical mixture used in the hopper was not performed by the pilot or the ground loading operations personnel as recommended by the manufacturer of one of the chemicals used. In addition, the technical sheet for one of the chemicals used contained a caution about a chemical foaming reaction when mixing it with other chemicals, one of which was also in the hopper. Due to the pilot’s view being obscured from foam originating from the hopper, the pilot was unable to maintain control and clearance from the terrain during the flight.

Text from the NTSB. Open the NTSB docket for CEN21LA286 for the full record.