Aircraft Accident/Incident Report

Denver, Colorado 80249
Friday, April 9, 2004 10:00 MDT

The captain reported that he had placed the windshield heat to the "normal" position and then called for the climb checklist. The captain said they were operating in and out of IMC conditions. As they were leveling off at 11,000 feet mean sea level (msl), the captain said, " ... we experienced a popping sound as the result of the first officer's windshield beginning to crack. There were 4 or 5 cracks that started from the bottom left hand corner of the windshield and reached the halfway point of the windshield. At that time and almost instantly we heard another pop and those same cracks continued up the entire length of the windshield." The captain said that after the window had cracked completely, he heard the first officer say, "it's burning." The captain said he asked him what was burning and he replied, "the windshield." The captain said he turned off the heat on his side of the windshield and removed his approach plates from the glare shield. He said he looked over to see what was going on, but did not see any smoke or fire. The captain said he called for the "cracked or shattered windshield checklist." They completed the checklist and landed the airplane uneventfully. The first officer said he noticed a constant spark at the bottom left corner of his windshield and brought it to the captain's attention. The first officer said they turned off the windshield anti-ice switch for his side and the spark stopped. "A few seconds later, my side of the windshield cracked in different places." An examination of the windshield showed six cracks in the outer pane originating at a location 6 inches inboard of the center post along the anti-ice terminal strip. Further examination of the windshield showed that the glass exhibited thermal damage and sooting between the glass layers at the origination point of the cracks, along the lower edge of the heating element. An examination of the hub seal, around the outer edge of the glass and aluminum frame showed evidence of deterioration. There was evidence of water intrusion between the glass plies. The intrusion damage extended along much of the lower edge of the windshield. The windshield heating element was corroded in the areas where water intrusion was observed. The airplane maintenance manual states that the primary cause of moisture ingress is a deteriorated seal. Moisture ingress eventually leads to one or all of the following: 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 called for during each of six 200-hour Detail Inspections.

arcing of the windshield deicing system. Factors contributing to the incident were the improper inspection of the windshield's exterior seal, deterioration of the windshield seal, and water penetration through the deteriorated seal.