Air carrier flight crew reported recovering safely from an inflight loss of control event related to strong turbulence at FL340.
Synopsis
Air carrier flight crew reported recovering safely from an inflight loss of control event related to strong turbulence at FL340.
Narrative
At cruise flight level 340 we were approaching the East Coast; but had to go through a line of precipitation. The weather radar showed only green scattered precipitation that was confirmed with WSI (Weather App) and Jepps weather mode FD pro. Nothing was reported in this area for turbulence. As we approached point SIVIK we heard an air carrier below us ask for a right deviation shortly thereafter our weather radar turned from green precipitation only to yellow with turbulence ahead so I immediately asked for a right deviation as well and in the right deviation turn; we encountered moderate turbulence initially causing 1000 foot per minute climb and disengaging the auto pilot. As it began to recover from the climb; we immediately ended up in a 2500 foot descent uncommanded with speed rapidly accelerating. I reduced throttle; deployed speed brake and began to pull up. We ended up 800 feet low at which point ATC queried if we were OK and we mentioned moderate turbulence encountered with uncommanded climbs and descent as we pushed through the line of weather. Air Traffic Control acknowledged and took a report from the other air carrier as well for moderate turbulence. We received direct to a follow on point with no further incident no injuries no damage to the aircraft.
Second reporter narrative
Aircraft X 'Coasting-In' with New York Center; at fix SAVIK FL340; aircraft weather radar did not show much of radar return; JEPPESEN Enroute Chart Weather Radar depicted light; medium and dark green with small yellow; WSI (Weather App) depicting accompanying/similar weather information; SkyPath not showing much for suspected lack of reporting aircraft; on the northern boundary of SIGMET with tops FL420. Started with heavy St. Elmo's Fire on the windshields; heavy rain; and light chop progressed into light turbulence and further into moderate turbulence. An air carrier aircraft was below us at FL320; SLOP'd (Strategic Lateral Offset Procedure) right. Moderate turbulence continued with large airspeed fluctuations which was corrected with throttle adjustment and speed brake usage; while auto throttle and autopilot was on. Moderate turbulence continued with aircraft rolling beyond 10 degrees right and left; with accompanying pitch changes; at which point the autopilot kicked off; pitch changes to 10-15 degrees first down then up; VVI (Vertical Velocity Indicator) noted at 2500fpm down; recovering to VVI 1000fpm up; altitude deviated down to FL330; recovering up to FL345; back to FL340. ATC called concerned with our deviations and Captain responded with description of conditions and recovering.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.