NTSB Identification: WPR12LA233
14 CFR Part 137: Agricultural
Accident occurred Sunday, May 27, 2012 in Wilton, CA
Probable Cause Approval Date: 11/26/2012
Aircraft: GRUMMAN ACFT ENG COR-SCHWEIZER G-164A, registration: N8380
Injuries: 1 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The pilot had just completed an aerial application of sulfur dust over a vineyard when the hopper gate closing mechanism failed as he attempted to stop the flow. The sulfur continued to flow from the hopper, so he initiated a steep turn to keep the dust within the confines of the vineyard. As he rolled out of the turn, the plume of sulfur ignited and a fire began within the hopper. He performed a forced landing into a residential driveway and the airplane sustained substantial damage during the ground roll.

The airplane was configured to minimize the hazards of inadvertent fire during sulfur dusting operations; however, the evasive flight maneuver performed by the pilot may have brought the uninterrupted flow of sulfur dust into contact with hot engine exhaust. An alternative ignition source may also have been provided by a spark from the failed gate mechanism. The gate mechanism sustained thermal damage, which prevented an accurate assessment of its failure mode.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The failure of the hopper gate mechanism and subsequent sulfur fire during a low-level maneuver.

Full narrative available

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