NTSB Factual Report

On July 22, 2004, approximately 2030 mountain daylight time, a Grumman G-164A, nosed over after experiencing a main landing gear collapse during a forced landing in an agricultural field about two miles west of Nyssa, Idaho. The commercial pilot, who was the sole occupant, received minor injuries, and the aircraft, which was owned and operated by the pilot, sustained substantial damage. The 14 CFR Part 137 aerial application flight, which departed a local agricultural airfield, had been airborne for about 10 minutes at the time of the accident. The flight was taking place in visual meteorological conditions. No flight plan had been filed.

According to the pilot, during one of his application runs there was a loud bang, and the engine suddenly lost a significant amount of power. Since it appeared that he did not have enough power to remain airborne, he elected to execute a forced landing in a nearby agricultural field. Although the initial touchdown was uneventful, the main gear of the aircraft dug into the soft terrain, leading to a main gear collapse and a nose-over of the aircraft. According to both the pilot and the FAA Inspector who responded to the accident, it was determined that while the aircraft was in flight, the number four cylinder head had fractured near where the cylinder head was screwed into the cylinder barrel. The FAA Inspector said that the fracture was of such a nature that it kept the cylinder from developing the compression necessary for detonation of the fuel/air mixture.

NTSB Probable Cause

The failure (fracture) of the number four cylinder head during an aerial application run. Factors include the soft crop-covered terrain.