Accident Overview
On August 11, 2010, at approximately 0715 Pacific daylight time, a Grumman Aircraft Engineering Corporation Schweizer G-164B, registration N6781K, suffered a loss of engine power while maneuvering to spray a field near Tracy, California. The aircraft was operated by Trinkle AG Flying Inc. under 14 Code of Federal Regulations Part 137 as an agricultural crop dusting flight. The commercial pilot, who was also the owner, was uninjured. The airplane sustained substantial damage to its wings, fuselage, and tail section. Visual meteorological conditions prevailed, and no flight plan had been filed.
Pilot Report
According to the pilot's interview with the National Transportation Safety Board investigator-in-charge, he had begun flying at approximately 0630 that morning. The accident flight was his second of the day. The airplane was loaded with 240 gallons of pesticide and about 35 gallons of fuel. While spraying a cornfield, the pilot heard a loud bang, followed by a loss of engine power and engine shaking. He executed a landing in an alfalfa field. The field was slick, and when he activated the left brake to intentionally ground loop the airplane, the brake did not respond. The airplane continued forward until it struck a fence at the end of the field and came to rest inverted in a nearby ditch adjacent to the alfalfa field.
Engine Examination
The engine was examined under the supervision of a Federal Aviation Administration inspector. The examination revealed a cracked head on the number five cylinder. Additionally, the connecting links for all cylinders except the number 7 cylinder were broken, and the master rod had sheared. Investigators were unable to determine whether the master rod or a connecting link failed first. No other anomalies were found with the airframe or the power plant.