On February 23, 2004, at 1416 central standard time, a Grumman G-164C single-engine agricultural biplane, N6721K, registered to and operated by Skarda Flying Service Inc., of Hazen, Arkansas, was destroyed when it impacted terrain while maneuvering during an aerial application flight near Hazen, Arkansas. The commercial pilot, who was the sole occupant, sustained fatal injuries. Visual meteorological conditions prevailed, and a flight plan was not filed for the 14 Code of Federal Regulations Part 137 aerial application flight. The local flight originated at 1216 from the Skarda/Tollville Airport (21AR) near Hazen, Arkansas. The operator reported in the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) that the pilot was performing an aerial application on a field approximately one-half mile east of 21AR. The pilot completed his fifth aerial application pass and initiated a right turn to return to the field to start his sixth pass. Subsequently, the airplane impacted terrain in a soft field approximately one-half mile north of the field where the pilot was spraying, and came to rest on its left side. During a telephone interview with the NTSB investigator-in-charge (IIC), a witness performing an aerial application on a field located to the north stated that as he finished a turn, he looked out to locate the other airplane spraying to the south of his location. The witness stated he saw the airplane in a right turn as it impacted terrain right wing first followed by the engine. Examination of the wreckage by an Federal Aviation Administration (FAA) inspector, who responded to the accident site, revealed both main landing gears were separated from the fuselage. The three-bladed propeller was separated from the hub and was located approximately 40 feet from the main wreckage. The propeller hub was separated from the engine and was located 60 feet from the main wreckage. All flight control surfaces were located within the debris path. The top and bottom wings were separated from the fuselage. The 1978-model Grumman G-164C biplane was configured for agricultural aerial applications, and was powered by a TPE331-6-52M turbine engine, serial number P20131C, driving a three-bladed constant speed Hartzell propeller. The operator of the airplane reported in the NTSB form 6120.1/2 that the airplane's most recent 100-hour inspection was completed on July 21, 2003, with an airframe total time of 6,213.1 hours, and an engine time of 2,602 hours since major overhaul. The airline transport rated pilot held a valid FAA class-II medical certificate, with no limitations or waivers. The date of his last medical examination was July 18, 2003. The operator reported that the pilot had accumulated a total flight time of 18,000 hours, 6,300-hours in the accident aircraft make and model. An autopsy on the pilot was performed by the Arkansas State Crime Laboratory, Medical Examiner Division, Little Rock, Arkansas. Toxicological tests were performed by the FAA's Civil Aeromedical Institute (CAMI) in Oklahoma City, Oklahoma. Tests were negative for drugs. At 1415, the Stuttgart Municipal Airport (SGT), near Stuttgart, Arkansas, automated surface observing system (ASOS), located approximately 11 nautical miles southwest of the accident site, reported sky clear, visibility 10 statue miles, wind from 160 degrees at 6 knots, temperature 61 degrees Fahrenheit, dew point 46 degrees Fahrenheit, and an altimeter setting of 29.94 inches of Mercury. Detailed examination and teardown of the engine and accessories was accomplished under the supervision of an FAA inspector at the Honeywell Engines, Systems, and Services Facilities, Phoenix, Arizona, on June 8, 2004. The examination revealed the prime mover exhibited impact damage. The accessory mounting studs were pulled out of the accessory case. The air inlet portion of the gear case assembly was fractured. The compressor, turbine, or propeller shaft would not rotate. The compressor blades were bent aft in the opposite direction of rotation with visual signs of dirt present. Internal components of the gear box rotated freely and appeared to be free of anomalies. The oil and fuel filters were absent of debris. The second stage turbine wheel disc exhibited radial/circumferential scraping against the third vane. Visual evidence of metal spray was observed on the trailing edges of the second stage turbine wheel blades. No anomalies were noted with the engine during the inspection.