History of Flight
On May 27, 2012, at approximately 0815 Pacific daylight time, a Grumman G-164A (registration N8380) operated by Harding Flying Service experienced an in-flight fire involving its chemical dispersal system. The airplane was being used for agricultural aerial application under 14 Code of Federal Regulations Part 137. The commercial pilot, who held a valid certificate, was not injured. The aircraft sustained substantial damage during the accident and was subsequently consumed by post-impact fire. The flight had departed from a private airstrip near Clarksburg, California, at about 0730. Visual meteorological conditions prevailed, and no flight plan had been filed.
Pilot Report
The pilot reported that he had just completed a pass over a vineyard applying sulfur dust. When he pulled the hopper gate lever to stop the flow, the lever became limp. Sulfur continued to discharge, prompting him to initiate a steep turn to confine the dust within the vineyard. As he rolled out of the turn, the sulfur plume ignited behind the airplane, and he heard a popping sound from the hopper, which was now on fire. He executed a forced landing into a residential driveway. During the ground roll, the main landing gear became embedded in soft dirt, causing the airplane to nose over.
Maintenance and Examination
Most non-steel components of the airplane were consumed by fire. FAA inspectors reviewed the maintenance records, which indicated the last annual inspection had been completed on January 16, 2012, at which time the aircraft had accumulated 12,376 flight hours since its manufacture in 1971. The FAA inspector confirmed compliance with Airworthiness Directive 48-34-02, which mandates features to reduce fire hazards during sulfur dusting operations. The gate mechanism was the original factory-installed system.
Examination of the hopper gate mechanism located beneath the cabin floor revealed that the hinge of the gate interconnect tube had separated from the gate lever. The hinge bolt remained in place and was attached to the remnants of the hinge. The mechanism had sustained thermal damage, preventing an accurate assessment of its fracture features. A review of the FAA Service Difficulty Report and Airworthiness Directive databases found no documentation of prior instances of this failure.