Air carrier flight crew reported encountering severe turbulence resulting in loss of aircraft control. The flight crew regained control of the aircraft and proceeded to their destination.
Synopsis
Air carrier flight crew reported encountering severe turbulence resulting in loss of aircraft control. The flight crew regained control of the aircraft and proceeded to their destination.
Narrative
While cruising at 35000 feet just prior to fix ZZZ we noticed a red dot on our weather software. We took action and made announcements and seat belt sign on and asked the Fas to be seated as well. Approx 3-5 minutes later we started getting turbulence moderate which quickly changed to severe We asked atc for lower and were unable 330 due to traffic and were told 90 seconds before we could descend . We were proactive and had already slowed to Mach .75 . We lost about 200 feet and gained 30-50 knots on airspeed indicator and then gained over 200 feet within seconds . After about 45 seconds I asked atc how much longer to descend and that we were in severe turbulence . Was told 30 more seconds due to traffic in area. The VSI was pitching upwards to 1200-1700 feet per minute however we only gained around 200feet and but airspeed then lost 30-40 knots. Autopilot was on and did a great job of correcting. Seat belt sign was on prior to encounter and after about 30-45 seconds we were given permission to descend to fl330. We were out of severe at approx 34400 feet and once below fl340 it was fairly smooth down to fl330 . We then had Fas check in and no injuries and no passengers were up during the event . I then notified dispatch we had descended to Fl330 as we did not have as we did not have a lot of reserve fuel . I then began messaging dispatch all the relevent info . Wrote up a Mx report and the rest of flight was uneventful.
Second reporter narrative
While cruising along at FL350 just prior to reaching ZZZ; I was pilot flying and noticed on our weather software a red dot up ahead at FL360 and lots of orange dots scattered around about 15 minutes in front of us. We had been having off and on smooth to light chop so the seatbelt sign was off at the current time. I turned the seatbelt sign on and the PA was made. We asked ATC about the rides ahead; and were told light to occasional moderate but 330 was a better ride but not smooth. I made the PA 'flight attendants take your jump seats in 2 minutes'; and started my timer. I then selected speed to Mach .76. The FO asked ATC to descent to FL330; we were told it would be a few minutes due to traffic below us. About 12 minutes after I started my timer we started getting constant moderate turbulence; that then progressed to severe turbulence. The FO asked ATC again about descending to FL330; stating we were in severe turbulence. ATC replied about 30 more seconds due to traffic below us. On the PFD we were showing airspeed fluctuations between a gain and loss of 30-40 knots; fortunately we had a large buffer between VMO with the airspeed at .76 turbulence penetration speed; so we never over-sped the aircraft. We also had an altitude gain and loss of 200 feet; while the vsi was showing rapid and abrupt changes between 1200 ft/min climbs and descents. I believe we were in the severe turbulence for about 2-3 minutes before ATC was able to get us FL330. The FO set the altitude and we immediately descended to FL330. Passing thru about FL345 it started smoothing out to light chop again. I asked the FO when he could get a message typed to send it to dispatch to let him know about the severe turbulence. We leveled at FL330; ATC asked about the ride; injuries and aircraft damage. I called the FAs and asked if everyone was ok in the back. They said everyone was fine as everyone was seated and I told them to stay in their seats and I would do the check in PA when appropriate. We reported to ATC and dispatch. We had a Jumpseater; I asked them if they noticed anything that I missed as jumpseaters usually see the bigger picture when they aren't focused on flying. They agreed with what we had discussed about the altitude and airspeed deviations and large trend vector changes and the time frame of the turbulence. After discussing more with dispatch and looking over the FOM info; we input a maintenance entry for the severe turbulence. I informed the purser that the turbulence we encountered was considered severe and she might get some phone calls or need to fill out some paperwork as well; so to check her manual. The rest of the flight continued uneventfully. Once we landed in ZZZ; after parking I called the Chief Pilot per FOM guidance.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.