Event Description
The captain reported that after selecting windshield heat to the normal position and calling for the climb checklist, the airplane was operating in and out of instrument meteorological conditions. As they leveled off at 11,000 feet mean sea level, a popping sound occurred as the first officer's windshield began to crack. Four to five cracks originated from the bottom left corner and reached the halfway point of the windshield. Almost instantly, another pop was heard, and the cracks continued up the entire length of the windshield. After the window fully cracked, the first officer said, "it's burning." The captain asked what was burning, and the first officer replied, "the windshield." The captain turned off the heat on his side and removed his approach plates from the glare shield. He looked over but did not see any smoke or fire. The captain called for the cracked or shattered windshield checklist. The crew completed the checklist and landed the airplane without further incident.
The first officer stated he noticed a constant spark at the bottom left corner of his windshield and brought it to the captain's attention. They turned off the windshield anti-ice switch for his side, and the spark stopped. A few seconds later, the windshield cracked in several places.
Examination Results
An examination of the windshield revealed six cracks in the outer pane, originating 6 inches inboard of the center post along the anti-ice terminal strip. Further inspection showed thermal damage and sooting between the glass layers at the origin point along the lower edge of the heating element. The hub seal around the outer edge of the glass and aluminum frame exhibited deterioration. Evidence of water intrusion between the glass plies was found, extending along much of the lower edge of the windshield. The windshield heating element was corroded in the areas where water intrusion was noted.
The airplane maintenance manual states that the primary cause of moisture ingress is a deteriorated seal. Moisture ingress can subsequently lead to delamination between the glass and interlayer, corrosion of the buss bar-heating wire junctions, failure of the electric heating system, and fracture of the outer glass ply. Inspection of the seal is required during each of six 200-hour Detail Inspections.