HISTORY OF FLIGHTOn March 27, 2018, about 1405 Pacific daylight time, a Schweizer Aircraft Corporation G-164B restricted category agricultural airplane, N3629E, was substantially damaged after colliding with high transmission power lines and a subsequent impact with terrain about 10 nautical miles southwest of Stockton, California. The commercial pilot was fatally injured. The airplane was owned and operated by Haley Flying Service of Tracy, California, as a Title 14 Code of Federal Regulations Part 137 agricultural application flight, and a flight plan was not filed. Visual meteorological conditions prevailed for the local flight, which had departed the operator's private airstrip about 30 minutes before the time of the accident. In a statement submitted to the National Transportation Safety Board (NTSB), a company ground crewman who witnessed the accident reported that the field being sprayed had transmission towers angling across it to support transmission power lines. After the pilot finished spraying the field in a north to south orientation, the witness advised the pilot to spray the area on the west side of the transmission towers to ensure proper coverage. As the witness watched the spray being dispensed, he saw "a flash," looked up, and observed the airplane impact the ground. The witness indicated, in a statement to local law enforcement personnel, that, while the pilot was flying southbound below and under two sets of high transmission power lines, the airplane clipped the second set of lines, which caused it to impact the ground nose first. There was no postimpact fire. PERSONNEL INFORMATIONThe pilot held a commercial pilot certificate with a rating for airplane single-engine land. His most recent Federal Aviation Administration (FAA) second-class medical certificate was issued on October 4, 2017, at which time he reported accumulating about 703 hours total flight experience and about 156 hours in the accident airplane make and model. The pilot completed his most recent flight review on April 16, 2016. AIRCRAFT INFORMATIONThe airplane's most recent annual inspection was performed on March 13, 2013, at a total time of 16,689.7 hours, with 17.2 hours since that last inspection. The airplane was equipped with a Honeywell TPE-331-201A turboprop engine, rated at 715 horsepower, with a total time of 15,520 hours. The operator indicated that there were no mechanical issues with either the airplane or the engine that would have precluded normal operation. AIRPORT INFORMATIONThe airplane's most recent annual inspection was performed on March 13, 2013, at a total time of 16,689.7 hours, with 17.2 hours since that last inspection. The airplane was equipped with a Honeywell TPE-331-201A turboprop engine, rated at 715 horsepower, with a total time of 15,520 hours. The operator indicated that there were no mechanical issues with either the airplane or the engine that would have precluded normal operation. MEDICAL AND PATHOLOGICAL INFORMATIONAn autopsy was performed by the Office of the Sheriff-Coroner, County of San Joaquin, French Camp, California. The autopsy determined that the pilot's cause of death was blunt force trauma. Toxicology testing performed at the FAA Forensic Sciences Laboratory identified doxylamine (an antihistamine) and dextrorphan (a cough suppressant) in the pilot's blood and urine specimens. No carbon monoxide was detected in the pilot's blood specimens, and no ethanol was detected in the pilot's vitreous specimens. Testing for cyanide was not performed.