Pilot's Account
The pilot of an agricultural airplane reported that he intended to apply a herbicide and test the spray system at maximum pressure while maintaining a specified airspeed. A ground tractor was also in the field applying the same chemical. During the flight, the pilot observed the tractor and flew over it at an altitude between 50 and 100 feet. While spraying at 10 feet above ground level, he monitored pressure, output, airspeed, and ground speed. At the end of the field, he climbed and executed a left 180-degree turn to begin another pass. The pilot stated that he "lost focus" outside the airplane while examining the spray results. When he noticed the tractor again, it was too late to avoid a collision; the airplane's wheel struck the tractor.
Tractor Driver's Account
The tractor driver reported that he heard someone call him on the radio and responded to the pilot. He then saw the airplane approaching "directly at him, very low." The driver heard and felt the impact, and the collision knocked him from his seat. He subsequently called his supervisor for assistance. The driver added that his supervisor and another ground sprayer had previously been "buzzed" by the pilot.
Aircraft Damage
Examination of the airplane revealed substantial damage to the fuselage.