Date: 201812
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: IMC
Light: Dawn
Aircraft: Regional Jet 900 (CRJ900)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Cockpit Window
Component problem: Failed; Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Second reporter function: First Officer
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Aircraft Aircraft Damaged; Flight Crew Landed As Precaution; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Diverted
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: At FL200 in cruise flight the First Officer noticed a flickering light on his side window. As I looked over I observed what looked like a strobe effect at the bottom of his side window. [Upon] further inspection we realized that the window had a growing crack. I immediately grabbed the QRH and looked up Window Arcing QRH. I turned off the RH windshield heat and the arcing continued and I told the FO (First Officer) to fasten his seatbelt and I was notifying the Flight Attendants that they needed to take their seats due to a window issue when the window shattered. At this time the FO completed the rest of the QRH and I was working the radio and notifying Dispatch. The FO showed me the Checklist which said that we needed to reduce our speed to 205 KIAS and descend to 8000 feet. I advised this to ATC. ATC cleared us direct to [a nearby alternate] and down to 8000 feet. I called the Flight Attendant back and advised her of [the deviation to an alternate] with 15 minutes remaining and that we planned to make a normal landing. I gave the normal briefing to the passengers that we were on our initial descent and would be [on the ground] in 15 minutes. We notified Dispatch of the event and told them what airspeed and altitude that we would continue on to [the alternate] at. We continued with no further incident. The window shattered due to a crack that formed at the bottom of the window.


Second narrative: While in cruise at FL200 I noticed a flashing light on the side window. I then noticed a hairline fracture forming from the bottom of the window moving up. The Captain began running the QRH for arcing window. After turning the RH heat off; he paused the checklist to contact the FA (Flight Attendant) to tell her what was going on and to be seated as a precaution. While he was talking to the FAs; the arcing became much brighter followed a few seconds later by a large bang and the window pane shattered. After verifying no change in cabin pressure; I began running the QRH while the Captain was still talking to the FAs and also to ATC and using ACARS to keep Dispatch and Maintenance in the loop. When the QRH asked if core ply or inboard ply shattered; I went with yes; because it appeared that it may have been the core ply. I could tell that it was not the inner ply. We told ATC that we needed to descend to 8000 feet and slow to 200kts. We proceeded direct to [an alternate] and landed without incident.


Synopsis: CRJ-900 flight crew reported diverting after the First Officer's windshield arced and shattered in cruise.