On July 28, 2009, about 1100 Pacific daylight time, a Grumman 164A, N8741H, collided with terrain during a forced landing following a loss of engine power near Riverdale, California. The commercial pilot sustained minor injuries. The local aerial application flight was operating in accordance with 14 Code of Federal Regulations (CFR) Part 137. Visual meteorological conditions prevailed at the time of the accident and a flight plan was not filed. The flight departed a private airstrip located about 12 miles north of the accident site 30 minutes prior to the accident. In a statement provided to the NTSB investigator-in-charge (IIC), the pilot reported that after having made about 18 passes on the alfalfa field he was spraying, he detected a hot smell. The pilot stated that he pulled up out of the field, checked his engine gauges, and that everything appeared normal; the pilot then proceeded to conduct his next spray pass. The pilot reported that after entering the field on the next spray pass "...the engine changed sound." The pilot stated that he pulled up out of the field a second time, checked the engine gauges again, and again everything was normal. The pilot stated that about this time "...the engine began to slow down. [I] added power, which took a few seconds and [it] began to slow down again. Also, it began to smoke out the exhaust." The pilot further stated that he decided to land in the field he was spraying. The landing was reported to be normal, but due to the wet condition of the field the airplane nosed over onto its back. On August 6, 2009, at the facilities of Aero-Engines of Los Angeles, California, a Federal Aviation Administration aviation safety inspector provided oversight during a teardown examination of the engine. The inspector reported the examination revealed that the engine failed due to a supercharger-blower failure. The inspector further reported that foreign object material was found in the engine, but it could not be determined if this was a contributing factor to the engine failure. The inspector reported that at the time of the accident the engine, a Pratt & Whitney 1340-59, serial number 325446, had accumulated a total of 835.27 hours since its last major overhaul (SMOH), and a total time of 7,792.8 hours. The inspector also noted that the manufacturer suggests a time between overhauls (TBO) of 600 to 1,000 hours for an engine used in agricultural work. The inspector further noted that the accident engine had a transfer case on the nose "...that will make more demands on the engine."