NTSB investigators traveled in support of this investigation and used data obtained from various sources to prepare this aircraft incident report.
The airplane suffered an in-flight fire at the right windshield terminal block while on approach to the destination airport. The flight crew donned oxygen masks, declared an emergency, landed without incident, and performed an emergency evacuation.
Examination of the windshield revealed that it had been installed on the airplane since manufacture more than 17 years prior to the incident, which far exceeded the average life of 8.2 years reported by the windshield manufacturer. The windshield exhibited typical signs of aging with ample evidence of moisture ingression into the laminate around the edges of the windshield. The aging discrepancies noted were within the published limits and did not contribute to the failure. The fire damage was concentrated in an area between the upper edge of the terminal block and the lower edge of the windshield gasket where the power wire was routed. The power wire was melted through in this area but remained soldered to the bottom of the terminal block indicating an arcing failure of the power wire. The damage and melting precluded determining if there was any pre-existing damage to the power wire prior to the incident. The arcing of the power wire produced enough localized heating to melt the glass and cause the fracture of the inner glass pane.
Examination of the maintenance records showed that the operator was in compliance with all recommended inspections from the airplane manufacturer, and the most recent inspection occurred more than 2 years and 3,500 flight hours prior to the incident with no discrepancies. The windshield manufacturer recommends inspection of the windshields at intervals significantly less than the airplane manufacturer.
The crew reported at least two attempts to extinguish the fire, but the fire continued, eventually extinguishing itself. The windshield heat selector switch was found in the normal position which would continue to provide power to the windshield heating system. Switching the windshield heat selector to off would have cut power to the circuit eliminating the arcing and fire. There is no training or guidance provided to the crew for windshield arcing, smoke, fire, or overheat events.