2025-04 · NASA ASRS report 2235604
B747-400 flight crew reported a windshield crack during cruise. The QRH procedures were completed and the flight diverted to a suitable airport where a safe landing was completed.
While enroute from ZZZZ-ZZZ; on RXXX between waypoints ZZZZZ and ZZZZZ1; I noticed a crack in the captain's forward window. I alerted the other Captain; who was in rest; and he came up to the cockpit and confirmed the presence of a crack. The three of us determined it to be an inner pane crack due to the fact that our fingernails would catch in the crack when passed over it. After we were all in agreement that we believed it to be an inner pane crack I called for the window damage checklist. We were unable to reach ZZZZ Radio on CPDLC or Primary or Secondary initially so I executed the oceanic contingency procedure to the right of course. After our offset was complete I began a checklist instructed normal descent to FL140 and initiated a turn back towards ZZZZ1. We were able to reach ZZZZ [ARTCC] after about 15 minutes and received a route clearance to proceed to ZZZZ1. We determined that we needed to jettison approximately 20 tons of fuel before arrival to reduce below maximum landing weight and to also mitigate a hot breaks situation with limited runway; rain; and one thrust reverser deferred.After jettisoning was complete we continued to ZZZZ1 without further incident. A logbook entry for a crack on the captains forward window was made. Cause: Cause of the crack is unknown.Suggestion: Communications while on oxygen can be very difficult the first time you do it in real time. Learning to speak and then toggle the interphone off so others don't hear the oxygen squeal of an inhale is something that should be taught. It was a significant distraction during the event. More thorough training should be given on identifying a suspected crack/scratch. Additionally; more training on whether it is an inner or outer pane crack would be helpful for situations like these.
After returning to the flight deck from my rest break; approximately 30 minutes prior to reaching ZZZZZ1; the captain informed me that he had noticed a crack on the inner pane of the left windshield and asked for my opinion. I agreed that it looked to be a crack as the line was uneven and both edges of the line were sharp. The captain then called the relief captain from the crew rest area to inspect the crack as well. Both captains did a tactile inspection and agreed that it was because their fingernails would get caught on the line when passed over it.The captain then requested the window damage checklist from the QRH which directed us to descend to 14000 feet. We were unable to establish contact with ZZZZ Radio on either the primary or secondary frequencies. The captain (PF) executed the oceanic contingency procedure; while I continued to attempt to make contact with ZZZZ Radio. I also sent a CPDLC stating our intention to descend and divert. Once the offset was completed we proceeded toward ZZZZ1. After approximately 15 minutes we re-established contact with ZZZZ Radio who cleared us a route to divert to ZZZZ1.While on route to ZZZZ1 we calculated that approximately 20 tons of fuel needed to be jettisoned to reduce the aircraft's weight below the maximum landing weight. This was necessary to mitigate the risk of hot brakes due to one thrust reverser being inoperative; as well as the wet runway conditions at ZZZZ1. Once the fuel jettison was complete; we proceeded to ZZZZ1 and conducted a normal landing.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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