NTSB Factual Report

On June 3, 2001, at approximately 0832 central daylight time, an Air Tractor, AT-402B, N484WB, operated by a commercial pilot was destroyed when maneuvering to reverse direction it impacted the terrain 4.5 miles northeast of Mount Vernon, South Dakota. Visual meteorological conditions prevailed at the time of the accident. The aerial application flight was being conducted under the provisions of 14 CFR Part 137. There was no flight plan on file. The pilot sustained fatal injuries. The local flight originated at Mitchell, South Dakota, at 0738.

A witness in the vicinity of the accident site said he was outside in his farmyard working when he heard an airplane working east of his farm. The witness said he saw the airplane a couple of times as it was making turns. The witness said he could hear the airplane's engine. He then heard a loud crash noise and didn't hear the airplane's engine anymore.

A Federal Aviation Administration (FAA) inspector examined the airplane at the accident site. On arrival, the inspector found the airplane in a grass field approximately 50 yards south of an east-west running line of trees. The front of the airplane, the propeller, and the engine, were buried in the ground. Impressions in the ground corresponded with where the leading edges of both wings came to rest. An arc-shaped slash in the ground was observed in the area around where the engine and cowling had impacted the ground. The propeller blades were buried in the ground so that only the blade tips were visible. The blades were curled aft at the tips. On removal of the airplane from the accident site, the propeller blades showed chordwise scratches and torsional bending. The propeller nose dome showed a crush angle of 30 degrees. The leading edges of both wings were bent upward and crushed aft. The cockpit and fuselage forward of the cockpit were crushed aft and broken forward and down. The main landing gear were broken aft. The aft fuselage showed skin wrinkles and a counter clockwise twist of approximately 15 degrees. The vertical stabilizer was bent and buckled forward. The rudder was intact. The right horizontal stabilizer and elevator were bent and broken forward. The left horizontal stabilizer showed skin wrinkles near the root. The left elevator was intact and showed no damage. Flight control continuity was confirmed. The airplane's engine, global positioning system (GPS) receiver, and flap actuator were retained for further examination.

An autopsy of the pilot was conducted by the staff pathologist at the Sioux Valley Hospital Morgue, Sioux Falls, South Dakota, on June 4, 2001.

FAA toxicology testing of specimens from the pilot showed trace levels of QUININE in blood. According to the FAA Toxicology and Accident Research Laboratory, the amount of quinine in the blood was not quantified because it was below the lab's cutoff. All other results were negative for all tests conducted. Quinine is found in tonic water and is used to treat severe malaria. It is also commonly used to reduce the frequency of nocturnal leg cramps - a condition which may cause painful leg muscle spasm at night, and was available over-the-counter for this purpose until 1995. According to an Aerospace Medical Association article, ingestion of quinine through tonic water can cause disturbances of vision, hearing, and balance. In social drinking, one study found that three drinks were likely to lead to a blood level of around 0.2 mg/dL. The article went on to state that blood levels of 0.2 mg/dL found at autopsy in pilots who died in aviation accidents in which positional cues seemed to be important suggest that quinine toxicity played a causative role.

According to the pilot's brother, tonic water was the pilot's favorite beverage. The night prior to the accident, the pilot was observed drinking tonic water with his dinner.

The GPS unit was examined at Sky-Tractor Supply, Hillsboro, North Dakota, on June 18, 2001. The examination revealed extensive damage to the internal components of the unit's hard drive. No data was retrieved from the unit.

The airplane's engine was examined at the Pratt and Whitney, Canada, Longueuil, Quebec, Canada, on October 31, 2001. No pre-impact anomalies were found with the engine.

NTSB Probable Cause

the pilot not maintaining aircraft control while maneuvering close to the ground.