Grumman G164 and Grumman G164 mid-air collision near Pleasant Grove, California, May 15, 2019

The NTSB's narrative for the Grumman G164 final · quoted from the NTSB record

The pilot of the white airplane departed to the south on the agricultural application flight, enroute to a field over which he was going to spread rice seed. At the same time, the pilot of the yellow airplane had just completed his agricultural application flight and was flying north/northwest to return to his departure airport. The two airplanes collided midair and subsequently impacted terrain; both pilots were fatally injured. Examination of the airplanes revealed no evidence of any mechanical malfunctions or anomalies. Day visual meteorological conditions prevailed in the area of the accident site at the time of the accident. Neither air traffic control radar data nor Automatic Dependent Surveillance – Broadcast (ADS-B) flight track information was available for either airplane. Autopsy of the pilot of the yellow airplane revealed severe coronary atherosclerosis and an enlarged heart, which placed him at increased risk for a sudden cardiac event including a heart attack or arrhythmia that could cause acute symptoms such as chest pain, shortness of breath, palpitations, or fainting without leaving evidence on autopsy of an acute event. However, given the circumstances of the accident, it is unlikely that the pilot’s medical condition was a factor in the accident. Toxicology testing revealed that the pilot of the yellow airplane had used cannabis. The primary psychoactive compound, THC, was found in his blood at a low concentration (1.7 ng/mL); the short-lived psychoactive metabolite 11-hydroxy-delta-9-THC was detected in urine and not blood. The non-psychoactive metabolite, THC-COOH, was found in blood and urine. THC blood concentrations in the first few hours after inhalation are commonly 50 times higher than what was found in the pilot’s blood, suggesting that the cannabis use was not within the last few hours. Since both THC and THC-COOH can be detected in blood weeks after using cannabis, concentrations cannot be used to demonstrate that the pilot was impaired at the time of the accident. While there may be residual effects from using cannabis, peak effects typically occur in the first few hours. Given the low concentration of the psychoactive compounds and the circumstances of the accident, it is unlikely that the effects of the pilot’s use of cannabis contributed to the accident. Based on the available information, it is likely that the pilots of both airplanes failed to see and avoid the other airplane, which resulted in a midair collision.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.

The NTSB's narrative for the Grumman G164 final · quoted from the NTSB record

The pilot of the white airplane departed to the south on the agricultural application flight, enroute to a field over which he was going to spread rice seed. At the same time, the pilot of the yellow airplane had just completed his agricultural application flight and was flying north/northwest to return to his departure airport. The two airplanes collided midair and subsequently impacted terrain; both pilots were fatally injured. Examination of the airplanes revealed no evidence of any mechanical malfunctions or anomalies. Day visual meteorological conditions prevailed in the area of the accident site at the time of the accident. Neither air traffic control radar data nor Automatic Dependent Surveillance – Broadcast (ADS-B) flight track information was available for either airplane. Autopsy of the pilot of the yellow airplane revealed severe coronary atherosclerosis and an enlarged heart, which placed him at increased risk for a sudden cardiac event including a heart attack or arrhythmia that could cause acute symptoms such as chest pain, shortness of breath, palpitations, or fainting without leaving evidence on autopsy of an acute event. However, given the circumstances of the accident, it is unlikely that the pilot’s medical condition was a factor in the accident. Toxicology testing revealed that the pilot of the yellow airplane had used cannabis. The primary psychoactive compound, THC, was found in his blood at a low concentration (1.7 ng/mL); the short-lived psychoactive metabolite 11-hydroxy-delta-9-THC was detected in urine and not blood. The non-psychoactive metabolite, THC-COOH, was found in blood and urine. THC blood concentrations in the first few hours after inhalation are commonly 50 times higher than what was found in the pilot’s blood, suggesting that the cannabis use was not within the last few hours. Since both THC and THC-COOH can be detected in blood weeks after using cannabis, concentrations cannot be used to demonstrate that the pilot was impaired at the time of the accident. While there may be residual effects from using cannabis, peak effects typically occur in the first few hours. Given the low concentration of the psychoactive compounds and the circumstances of the accident, it is unlikely that the effects of the pilot’s use of cannabis contributed to the accident. Based on the available information, it is likely that the pilots of both airplanes failed to see and avoid the other airplane, which resulted in a midair collision.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.

Other NTSB records under N6787K the same tail number, which may have belonged to a different aircraft at the time