The Latah County Sheriff's Office said 60-year-old Randy Humble of Moscow died in the crash around 5:30 p.m. Saturday near the town of Viola.
Latah County Republicans were holding their annual fundraiser and picnic at the time.
The sheriff's office said witnesses reported hearing the aircraft's engine revving loudly just before it crashed.
The pilot was alone in the plane and died at the scene.
The FAA will launch an investigation into what caused the crash.
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