Narrative:

The aircraft was in cruise at FL210 and operations were normal. It was minus 17C out and the windshield heat was functional and had been on since departure from a plus 1C airport. We had been at cruise for about 30 minutes when there was a loud pop and an instantaneous spider web fracturing of the left panel of the windshield. The fracturing began on the right and travelled towards the left across 95 percent of the surface area. I felt small flecks of something hit my forehead and later noticed a few small flecks resting on the glareshield. My passengers reported that when the fracturing occurred; they felt a change in the airflow in the cabin. The cabin did not depressurize. I ran the abnormal checklist for a cracked/shattered windshield and called ATC requesting a descent and divert to an airport in VMC conditions within 50nm. The forward visibility through the windshield was minimal. During the descent I could hear the windshield continue to fracture; though slowly. (A picture taken after landing; compared to a picture taken by a passenger when the event first occurred; did show the fractures had increased.) I could not tell at the time if both the inner and outer ply were compromised. I landed at the divert airport without further incident. It was challenging to see clearly through the windshield and I had to look out of a small unblemished spot in the lower left to land. The left panel of the windshield has a documented history of more than 3 years of slight delamination in the lower right corner. That spot has been periodically inspected; marked; and signed off as acceptable. Within the previous month a pilot had reported that the delamination had grown slightly beyond the markings. As a result; a qualified maintenance person inspected; re-marked; and signed the windshield panel off as acceptable.

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Original NASA ASRS Text

Title: A BE9L pilot reported deviating to an alternate airport after the left cockpit window fractured in cruise at FL210.

Narrative: The aircraft was in cruise at FL210 and operations were normal. It was minus 17C out and the windshield heat was functional and had been on since departure from a plus 1C airport. We had been at cruise for about 30 minutes when there was a loud pop and an instantaneous spider web fracturing of the left panel of the windshield. The fracturing began on the right and travelled towards the left across 95 percent of the surface area. I felt small flecks of something hit my forehead and later noticed a few small flecks resting on the glareshield. My passengers reported that when the fracturing occurred; they felt a change in the airflow in the cabin. The cabin did not depressurize. I ran the abnormal checklist for a cracked/shattered windshield and called ATC requesting a descent and divert to an airport in VMC conditions within 50nm. The forward visibility through the windshield was minimal. During the descent I could hear the windshield continue to fracture; though slowly. (A picture taken after landing; compared to a picture taken by a passenger when the event first occurred; did show the fractures had increased.) I could not tell at the time if both the inner and outer ply were compromised. I landed at the divert airport without further incident. It was challenging to see clearly through the windshield and I had to look out of a small unblemished spot in the lower left to land. The left panel of the windshield has a documented history of more than 3 years of slight delamination in the lower right corner. That spot has been periodically inspected; marked; and signed off as acceptable. Within the previous month a pilot had reported that the delamination had grown slightly beyond the markings. As a result; a qualified maintenance person inspected; re-marked; and signed the windshield panel off as acceptable.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.