Narrative:

I was acting as a co-captain; conducting pilot not flying duties. We departed ZZZ1 just after sunset and were eventually cleared to FL210. After approximately 30 minutes in cruise I heard a loud bang and noticed along with the pilot flying that the pilot side windshield had developed numerous spiderweb type cracks in it. I requested an immediate descent and was cleared to 10;000 ft. We conducted an emergency descent procedure to that altitude and subsequently declared an emergency. We decided to divert the aircraft to a nearer airfield due to ZZZ2 still being more than 1 hour away. We initially decided upon ZZZ3 however ZZZ3 was experiencing low visibility and ceilings. After obtaining further weather information from center on possible alternates we decided to divert to ZZZ. Due to not knowing the extent of damage to the windshield the left seat captain and I decided that it was safer for him to get out of the left seat and sit in the seat immediately behind the right side pilot seat. The aircraft was configured to allow him to have full access to the radios from that seat; so he took over pilot not flying duties while I transitioned to pilot flying. We received radar vectors to the final approach course for the ILS. I flew an uneventful approach into 2-3 mile visibility with blowing snow and ceilings approximately 2;000-3;000 ft. The runway had compacted snow and minimal ice and the braking action was reported as good. I found this to be true as we landed uneventfully. We taxied to the FBO and secured the aircraft. I did not complete a discrepancy log for this particular discrepancy prior to leaving the airplane. I believe that crew coordination during this flight was excellent; we both communicated very well; knew each others intentions; discussed options and agreed on courses of action promptly and safely.

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Original NASA ASRS Text

Title: BE90 First Officer reports Captain's side window failure at FL210 and decision to divert to nearest suitable airport.

Narrative: I was acting as a co-Captain; conducting Pilot Not Flying duties. We departed ZZZ1 just after sunset and were eventually cleared to FL210. After approximately 30 minutes in cruise I heard a loud bang and noticed along with the Pilot Flying that the Pilot side windshield had developed numerous spiderweb type cracks in it. I requested an immediate descent and was cleared to 10;000 FT. We conducted an emergency descent procedure to that altitude and subsequently declared an emergency. We decided to divert the aircraft to a nearer airfield due to ZZZ2 still being more than 1 hour away. We initially decided upon ZZZ3 however ZZZ3 was experiencing low visibility and ceilings. After obtaining further weather information from Center on possible alternates we decided to divert to ZZZ. Due to not knowing the extent of damage to the windshield the Left Seat Captain and I decided that it was safer for him to get out of the left seat and sit in the seat immediately behind the right side Pilot seat. The aircraft was configured to allow him to have full access to the radios from that seat; so he took over Pilot Not Flying duties while I transitioned to Pilot Flying. We received radar vectors to the final approach course for the ILS. I flew an uneventful approach into 2-3 mile visibility with blowing snow and ceilings approximately 2;000-3;000 FT. The runway had compacted snow and minimal ice and the braking action was reported as good. I found this to be true as we landed uneventfully. We taxied to the FBO and secured the aircraft. I did not complete a discrepancy log for this particular discrepancy prior to leaving the airplane. I believe that crew coordination during this flight was excellent; we both communicated very well; knew each others intentions; discussed options and agreed on courses of action promptly and safely.

Data retrieved from NASA's ASRS site as of April 2012 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.