History of Flight
On August 6, 2023, about 0927 Pacific daylight time, a Grumman G164A (registration N5450) sustained substantial damage in an accident near Davis, California. The pilot sustained fatal injuries. The airplane was being operated as a Title 14 Code of Federal Regulations Part 137 aerial application flight. The purpose of the flight was to apply pesticide to a local tomato crop. According to the operator, the airplane was topped off with fuel and 1,700 lbs of pesticide the night before. On the morning of the accident, the pilot departed from Medlock Field Airport (69CL) in Woodland, California, and conducted aerial applications while flying from west to east about 68 ft above ground level. An employee responsible for refueling and loading the hopper reported that the airplane was fueled to about three-quarters of a full tank and he added 1,500 lbs of pesticide before the accident. The employee continued with daily tasks and did not witness the accident. There were no witnesses.
Personnel Information
No pilot logbooks were recovered or provided during the investigation.
Aircraft Information
The operator identified the insecticide used as Wilbur-Ellis BEN-SUL 85. According to the United States Environmental Protection Agency Pesticide Product Label, the pesticide contained 85 percent sulfur and is marked with a caution: “Harmful if absorbed through the skin. Causes eye irritation. Avoid contact with skin, eyes or clothing.” The operator reported that the accident airplane was used solely for aerial applications of this pesticide. The operator provided airframe, engine, and propeller logbooks from the last annual inspection, which was less than one month before the accident, on July 31, 2023. No additional logbook entries were provided.
Meteorological Information
The weather at an airport about 12 nautical miles from the accident site included a temperature of 82°F and a dew point of 59°F. The calculated relative humidity was 46 percent. Review of the icing probability chart in Federal Aviation Administration Special Airworthiness Information Bulletin CE-09-35 indicated that the atmospheric conditions at the time were conducive to serious icing at glide power.
Wreckage and Impact Information
Postaccident examination of ground scars and the resting position revealed that the airplane landed on the soft field and nosed over. A fire consumed the wreckage; the operator reported that the pilot self-extricated and was transported to a nearby medical facility. Ground scars consistent with the landing were about 93 ft east of the main wreckage. The wreckage came to rest inverted in the field where the pilot was applying pesticide. Fire consumed the engine compartment, fuselage, and empennage. The airplane sustained substantial impact and thermal damage; due to the damage, the investigation could not identify the source of the fire or determine if it began in flight. The left and right upper and lower wings sustained impact damage to the leading edges, with thermal damage emanating from the wing roots. The engine separated from the engine mount and came to rest about 4 ft from the main wreckage.
Examination of the recovered wreckage revealed that the cockpit was mostly consumed by fire except for the steel tube frame, which was thermally damaged but intact. Flight control continuity was observed. The fuel system was completely consumed by fire. Examination of the engine showed separation from the airframe but it remained attached to the engine mount structure. No holes were observed in the engine cases. All nine cylinders remained attached and secured to the intermediate case. The rear case and engine accessories exhibited thermal damage. Damage to the magneto prevented a functional test. The carburetor, generator, and remains of the magneto were removed from the rear case and the front spark plugs were removed from each cylinder. The propeller was rotated by hand throughout 360°. Rotational continuity was established throughout the engine and valvetrain, with movement observed on all rear accessory case gears. Thumb compression was obtained on all cylinders except for Nos. 5 and 9. Each cylinder was examined internally using a lighted borescope. Varying degrees of corrosion, water, oil, and dirt were observed in each cylinder. All intake and exhaust valves, pistons, and internal areas of each cylinder were unremarkable except for cylinders Nos. 5 and 9, in which the intake and exhaust seats exhibited an abundance of dirt debris. All front spark plugs exhibited normal operation signatures. The oil screen contained a small amount of melted metallic debris. A visual examination of the carburetor revealed impact and thermal damage. The throttle and mixture control ends remained attached to their respective controls on the carburetor. The jet covers were removed and both metering jets were found secure. The carburetor could not be disassembled due to impact damage.
Medical and Pathological Information
An autopsy of the pilot was performed by the Sacramento County Department of the Coroner. According to the autopsy report, the cause of death was complications associated with thermal injuries. The pilot succumbed to his injuries 25 days after the accident.