Accident Overview
On July 28, 2009, at approximately 1100 Pacific daylight time, a Grumman 164A, registration N8741H, collided with terrain during a forced landing following a loss of engine power near Riverdale, California. The commercial pilot, who was conducting an aerial application flight under 14 Code of Federal Regulations Part 137, sustained minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed. The flight had departed a private airstrip located about 12 miles north of the accident site approximately 30 minutes prior.
Pilot's Account
According to a statement provided to the NTSB investigator-in-charge, the pilot reported that after completing about 18 passes on the alfalfa field he was spraying, he detected a hot smell. He pulled up out of the field, checked his engine gauges, and found everything appeared normal. The pilot then proceeded with his next spray pass. After entering the field on that pass, the engine changed sound. The pilot again pulled up, checked the gauges, and again everything was normal. Shortly thereafter, the engine began to slow down. The pilot added power, which took a few seconds, but the engine began to slow down again and began to emit smoke from the exhaust. The pilot decided to land in the field he was spraying. The landing was reported as normal, but due to the wet condition of the field, the airplane nosed over onto its back.
Engine Examination
On August 6, 2009, at Aero-Engines of Los Angeles, California, a Federal Aviation Administration aviation safety inspector oversaw a teardown examination of the engine. The inspector reported that the examination revealed the engine failed due to a supercharger-blower failure. Foreign object material was found in the engine, but it could not be determined whether this was a contributing factor to the engine failure.
Engine Details
The engine was a Pratt & Whitney 1340-59, serial number 325446. At the time of the accident, it 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 noted that the manufacturer suggests a time between overhauls (TBO) of 600 to 1,000 hours for an engine used in agricultural work. Additionally, the inspector noted that the accident engine had a transfer case on the nose that would make more demands on the engine.