Air carrier B737NG flight crew reported encountering turbulence climbing through FL343 that resulted in an uncommanded bank angle of 45 degrees. Aircraft control was re-established using upset recovery procedures.
Synopsis
Air carrier B737NG flight crew reported encountering turbulence climbing through FL343 that resulted in an uncommanded bank angle of 45 degrees. Aircraft control was re-established using upset recovery procedures.
Narrative
While in cruise climb from FL330 to FL370; we encountered an abrupt left roll and shudder [from] turbulence out of FL343. Autopilot limits were exceeded and it disconnected without input due to amber roll authority message. Upset call outs and procedures were used and executed. The entire event onset and recovery lasted about 6 seconds. Conditions during the event were VMC all the way to the ground with a few storms 100 miles east off the coastline. Tops of the weather estimated around FL300. The seat belt sign was off at the time of the event and the FA's (Flight Attendant) were completing first class and coach service. To that point in the flight; we had experienced no turbulence at all. When FA's checked in; I was told all passengers were all seated at the time of the event and they had spilled liquids in the galley. I waited to write up the event for maintenance till ZZZ due to guidelines they require and not being familiar with them. The question from ATC was about wake turbulence. However; at the time of the event; the only traffic was at FL350 about 30 miles ahead with quartering headwinds on the same track. I believed the event to be be unrelated as aircraft rolled abruptly left so quickly.
Second reporter narrative
The Autopilot was on and flying in LNAV and VNAV. We started our climb from FL330 to FL370. Around FL342; the plane started to get turbulence. Then it rolled to the left. The autopilot kicked off and the bank went to 45 degrees. We started the upset recovery and got the plane back under control.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.