De Havilland DHC8 near Keene, NH — 2019-12-09

Probable cause

The arcing failure of the windshield heat L2 power wire on the right windshield due to unknown reasons.

NTSB narrative

While on descent to the destination airport, an in-flight fire occurred at the right windshield terminal block. The flight crew put on oxygen masks and smoke goggles, extinguished the fire, and landed without incident. 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 L2 power wire was routed. The L2 power wire was melted through in this area but remained intact on either side, indicating an arcing failure of the L2 power wire. The damage and melting precluded determination of whether there was any pre-existing damage to the L2 power wire before the incident. Examination of the windshield revealed that it had been installed on the airplane about 5 years before the incident, which was less than the 8.2-year average life reported by the windshield manufacturer. The windshield exhibited minor evidence of moisture ingression into the laminate around the edges and minor erosion of the exterior hump seal that did not contribute to the event. Review of the maintenance records showed that the operator was in compliance with all of the company and airplane manufacturer’s recommended inspections. The operator had performed the mandated inspections required by Airworthiness Directive (AD) but the application of Humiseal to the power terminals had not been completed, therefore, the operator was not in compliance with the AD. The missing Humiseal did not contribute to the event. The most recent inspection, which showed no discrepancies, occurred about 6 weeks prior to the incident.

NTSB coding

• Fire/smoke (non-impact) · Enroute-descent

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