This incident occurred on May 14th when a United Boeing 787-9 was taking off from Hong Kong to San-Francisco and several hours after takeoff it suffered a windshield crack. Because of this, the aircraft was diverted to the nearest airport, which was Tokyo Narita on May 15th.
Info about the flight
The registration no. was UA-2862 and the departure occurred about a day later than its schedule. There was a crew of 4 onboard just when they were a bit west of Tokyo Narita airport the windshield cracked. The team declared a PAN-PAN which is an emergency signal or indication to those helping on landing. The aircraft then turned towards its east to Narita Airport.
Why does a cracked windshield occur
It occurs mainly because of very low temperatures or massively high pressure or wind. It also happens because of looseness from hailstorms or a bird strike. The windshield is equipped with heating and several layers of windows for durability in the sky. Another reason is loose bolts holding the window. It can also happen because of a lot of heavy use.
Images taken from-