Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe; Deviation - Speed All Types; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued New Clearance; Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action
Weather
I was the Pilot flying when we encountered unexpected severe turbulence at FL270; autopilot was engaged. The Captain (CA) immediately made a PA for the Flight Attendants (FA) to take their seats; seatbelt sign was on. He asked for a climb; ride and WX info from ATC. We received only a climb clearance to FL310 and I initiated the climb. Climbing through FL290 ATC indicated a report of moderate turbulence at FL340; 160 miles ahead. We stopped our climb and began a descent back to FL290 to open up air speed (A/S) window and to clarify ride conditions at the higher altitude. ATC then gave us a frequency change and advised to check with next controller for ride/WX info. We received very little information from ATC but FL290 continued to be extremely turbulent; so we asked and received clearance to FL340; then ultimately to FL350. We were heavy and climb was slow with 175+ kts of tail wind. During this time and through all altitudes we experience several occurrences of severe turbulence with periods of moderate and light turbulence/chop in-between. The event lasted approximately 30-40 minutes. The auto pilot remained coupled throughout the entire event. Even though every attempt was made to maintain control of the aircraft we still exceeded airspeed limitations and made assumptions that the G-load limitations may have also been exceeded after speaking with maintenance. ATC gave no indication of potential WX problems prior to; or during; the event. The CA began communication and coordination with the FA's and relief pilots in the cabin during and after the event to assess damage. The relief pilots had been on break in the crew rest bunks during the event. I continued to fly the aircraft while also communicating with ATC and preparing for oceanic entry and establishing HF com and SELCAL. We accumulated info from the relief pilots and FA's on the condition in the cabin and any known injuries. The CA also communicated with dispatch; ATC and maintenance to evaluate WX; best route and destination as well as the integrity of the aircraft. The CA determined the best course of action was to proceed to ZZZZ. The CA ask dispatch to plan a course to prevent flight back into the WX we had experienced. We received routing from dispatch; asked for; received and initiated clearance ZZZZ. The turbulence event lasted; approximately 30-40 minutes. This was the worst sustained turbulence I had ever been through in my 25+ years of experience as a commercial airline pilot. We had no indication this WX existed on our flight plan; WX radar or from ATC. Better real time resources in the cockpit; like the ability to retrieve ground base WX radar and information while in flight. This may not have prevented this particular event because dispatch had indicated smooth rides on our flight plan and we had no radar returns or ATC warnings for us to expect anything; but having a current picture of your entire route would help tremendously in planning diversions or even planning best deviation courses enroute. This could save time and fuel in the long run; not to mention gives us another tool to possibly help prevent injury and damage to our aircraft.
Air carrier First Officer reports encountering unforecasted severe turbulence over the Pacific Ocean. The crew elects to divert to check for possible aircraft damage.