NTSB Factual Report

HISTORY OF FLIGHT

On April 9, 2004, at approximately 1000 mountain daylight time, a Beech 1900D, N210GL, operated by Great Lakes Aviation, Incorporated, sustained a cracked copilot's windshield when the airplane's windshield anti-ice system was activated. Subsequent arcing and smoke was observed originating from a terminal block for the anti-ice system. The crew took remedial action and subsequently made an uneventful landing at the Denver International Airport (DEN), Denver, Colorado. The incident occurred during cruise flight approximately 45 miles north of the Pueblo Municipal Airport (PUB), Pueblo, Colorado. Instrument meteorological conditions (IMC) prevailed at the time of the incident. The positioning flight from PUB, to DEN, was being conducted on an instrument flight rules flight plan under the provisions of Title 14 CFR Part 91. The captain and first officer on board reported no injuries. The flight originated at approximately 0930.

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), approximately 45 nautical miles north of the Pueblo VOR 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 continued to Denver where they landed the airplane uneventfully.

The first officer said they were in level cruise at 11,000 feet msl, and 9 miles east of Colorado Springs, Colorado, when he noticed constant sparking at the bottom left corner of his windshield. He said he brought it to the captain's attention. The first officer said they turned off the windshield anti-ice switch for his side and the sparking stopped. The first officer said, "A few seconds later, my side of the windshield cracked in different places."

Both crew members reported the outside air temperature as minus 12 degrees Celsius.

TESTS AND RESEARCH

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. Approximately 1 inch of the terminal strip, just beneath the crack origins, was melted. Four of the cracks extended from the origin outward to the right outboard post. They were located approximately 2 to 5 inches up from the bottom of the windshield. Two of the cracks ran upward from the origin to the top of the window. One crack was located 4 inches outboard of the center post. The other crack was located 7 to 8 inches outboard of the center post. A blackened area, approximately 6 inches long and 1-1/4 inch wide ran outboard along the anti-ice strip from the crack origin for approximately 6 inches. An area of brown discoloration began at the outboard edge of the blackened area. The area was approximately 10 inches long and 3 inches wide.

Further examination of the windshield was conducted in Wichita, Kansas, on April 23, 2004. The windshield, part number 1010-384025-18, had 2,716.1 hours total time since new. The windshield had been rebuilt in May 2001. An extra temperature sensor and terminal block had been added to the original windshield.

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. The seal showed areas where it had come loose from the frame. Several cracks were observed in the seal material. Additionally, 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.

ADDITIONAL INFORMATION

Parties to the investigation were the Federal Aviation Administration, Denver, Colorado, Great Lakes Aviation, and the Raytheon Aircraft Company.

All retained components were released and returned to Great Lakes Aviation.

The Beech 1900D Airliner Maintenance Manual contains inspection criteria for the windshield. Chapter 56-10-00 Flight Compartment - Maintenance Practices, WINDSHIELD WEATHER SEAL INSPECTION AND REPAIR, states:

SEAL INSPECTION

Inspect the weather seal between the glass and the windshield retainer at the interval specified in Chapter 5-20-00.

Chapter 5-20-00 CONTINUOUS INSPECTION PROGRAM, Chart 201 CONTINUOUS INSPECTION SCHEDULE, indicates the windshield weather seal should be inspected during each of six 200-hour Detail Inspections.

Chapter 56-00-00 Flight Compartment - Maintenance Practices, WINDSHIELD REPLACEMENT CRITERIA, states:

f. Moisture Damage: The primary cause of moisture ingress is a deteriorated weather seal, Moisture ingress caused by a deteriorated weather seal will eventually lead to one or all of the following windshield degradation modes:

1. Delamination between the glass and the PVB interlayer (Separation between glass and interlayer characterized by a separation line with a different reflection characteristic on each side of the line).

2. Corrosion of the bus bar - heating wire junctions.

3. Failure of the electric heating system.

4. Outer glass ply fracture.

If the windshield is severely degraded due to any or all of the above conditions, the useful service life is limited and is cause for windshield replacement.

NTSB Probable Cause

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.