What happened
While climbing through 17,000 feet, the captain of the aircraft noticed the smell of smoke in the cockpit. Shortly after, flames and smoke began exiting from the lower left windshield. The captain suspected the source was the windshield heat unit. Upon turning off the windshield heat, the flames ceased, although smoke continued to enter the cabin. The captain declared an emergency with air traffic controllers and initiated a return to the Asheville Regional Airport.
The investigation
An examination of the windshield was conducted to determine the source of the fire. Investigators found that overheat damage had occurred due to an improperly installed fastener. This installation error caused electrical arcing between the terminal block lug, the aircraft wiring eyelet, and the fastener and lock washer used to secure the components. This arcing progressed over time, degrading the solder junction between the terminal block and the windshield heating system braid wire. This degradation led to heat damage in the sealant and the subsequent appearance of flames.