N709PS

An evaluation of the fracture pattern indicated that the outboard glass ply failed due to a fracture along the bottom aft edge of the window.

The conductive film interlayer located under the outboard ply reached a high enough temperature during the arcing event that it melted and fractured the outboard glass ply of the window. The arc escaped via the glass fracture, allowing the arc to come into contact with and melt the humpseal sealant. There were no indications of any burning or fire events on the inboard surface of the window (including the power terminal block).

The event was contained to the outboard glass ply. The power terminal block was removed, and no damage was noted to the wiring and solder connections.

There was evidence of moisture ingress and degradation of the interlayer of window was noted in some areas around the periphery of window. Humpseal degradation and improper humpseal repair techniques were noted.