What happened
The incident occurred during the takeoff phase of flight from an unimproved airstrip. The aircraft failed to achieve lift-off and subsequently ran off the end of the available runway surface. Prior to the attempt, the pilot reported that ambient air temperatures were high and that the airplane felt excessively heavy for the conditions.
In an effort to reduce the aircraft's weight to facilitate takeoff, the pilot attempted to jettison the chemical load. However, this procedure was unsuccessful because the air intake for the dump mechanism had become fouled by grass and brush debris. Consequently, the chemicals remained on board, contributing to the inability of the aircraft to gain sufficient altitude.
The investigation
Examination of the event revealed that the mechanical failure of the chemical dump system was directly linked to environmental contamination. The air intake responsible for operating the dump mechanism was obstructed by vegetation, specifically grass and brush, which prevented the system from functioning as intended.
Findings
Contributing factors included the high ambient temperature, which reduced air density and aircraft performance, and the mechanical obstruction of the chemical dump system. The pilot's assessment that the airplane felt heavy was consistent with the inability to jettison the load due to the fouled intake.