Date: 201507
Local time of day: 1201-1800
Location: ZZZZ.Airport, FO
Flight conditions: IMC
Weather elements / visibility: Turbulence; Hail; Rain
Light: Daylight
Aircraft: B787-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
ATC / advisory: Center ZZZZ
Aircraft component: Cockpit Window
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain; Check Pilot
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: Relief Pilot; First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Aircraft Damaged; Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport
Contributing factors: Weather; Aircraft; Procedure
Primary problem: Weather

Narrative: Weather Event. Cracked L2 window.


Second narrative: I was FC on the flight. I did my normal duties of the outside walk-around prior to leaving. About 10 minutes prior to departure time we received a normal clearance via voice. We had a normal push back; start-up and taxi. The initial climb out was normal and soon after 10;000 feet I began to figure out the break times for the flight. I could see weather ahead on the Captain's radar and knew we would have to deviate right; which we did. It was extremely difficult to get a word in on the radio; but FO was able to get a turn from approximately 060 degrees to heading 090. It soon became obvious we would need more of a deviation to stay out of the weather. FO repeatedly tried to get a further deviation. There was constant chatter on the frequency and we were not able to get a further vector so Captain elected to turn further anyway. We were outside the edge of the weather when it suddenly became extremely loud in the cockpit because of; what I thought was; heavy rain. It was evident later that we were in hail; although I never saw hail. The noise from the hail/rain lasted approximately 2 minutes. It was basically a white-out during which we experienced severe turbulence for maybe 10 seconds. During the turbulence at FL210 we got an altitude warning. I am not sure how far off our altitude we became. After the turbulence subsided we realized the Captain's left window was cracked and our weather radar was inoperative. We could also hear a groan/humming noise coming from the radome area. Captain told FO to tell ATC we had to return. It was decided that we would land overweight rather than dump fuel. I figured the landing distance for the overweight landing and determined the departure runway was sufficient. FB (Relief Officer) called Dispatch and Operations to inform them we were on our way back. Captain landed gently and used most of the runway to slow. We exited the runway and stopped the airplane. We did not set the brakes. It was difficult for ground control to understand we needed the brakes to be checked for overheating. Eventually; they understood and asked us to shut down the engines so the inspection could be made. After the inspection we were towed to a hardstand where we were met by station personnel. The passengers and crew were able to exit the airplane via airstairs.


Synopsis: B787 flight crew encountered a thunderstorm at FL210 during departure. Hail caused the L2 window to crack and apparently caused the Radar to fail. The crew elected to return to the departure airport for an overweight landing.