A300 flight crew reported loss of aircraft control and autopilot disconnect while flying through severe turbulence during cruise descent. Flight crew regained control and continued flight.
Synopsis
A300 flight crew reported loss of aircraft control and autopilot disconnect while flying through severe turbulence during cruise descent. Flight crew regained control and continued flight.
Narrative
While navigating direct ZZZ [VOR] from ZZZZZ1 at FL300; ATC ZZZ Center notified us of two areas of convective activity along our route of flight to ZZZ. We requested and were approved a left 10-degree deviation for weather. Our heading; 180; kept us outside of 20 NM from thunderstorms. ATC cleared us when able" direct ZZZZZ - fix on the ZZZZZ STAR into ZZZ. Once proceeding direct ZZZZZ; ATC cleared us to cross 70 NM north of ZZZZZ at FL280. Approximately 100 NM north of ZZZZZ; we commenced our descent to FL280 from FL300 at 280 KIAS in LEVEL/CHANGE - autothrottles maintain speed on pitch. While IMC; clear of any convective activity we encountered severe turbulence for approximately 30 seconds while descending through FL295 until FL285. We experienced a momentary downdraft with 2000 FPM rate-of-descent; displayed on the Vertical Speed Indicator; VSI; followed by a momentary updraft with approximately 500 FPM rate-of-climb; on the VSI. During this excessive altitude oscillation; the aircraft's ATS (Autothrottle System) Arming Lever and the #2 Yaw Damper Arming Lever disengaged and were immediately manually reengaged and remained armed/engaged for the remainder of the flight. The Left ECAM also momentarily displayed YELLOW HYD SYS LO PR; but then extinguished without any corrective action. During level-off at FL280 the Autopilot #2; AP2; lever also disengaged; but was reengaged without issue for the remainder of the flight. We advised ATC that we were experiencing extreme/severe turbulence during the event. ATC then queried if there were any injuries or damage to the aircraft and we advised ATC there were no injuries or damage.Our filed route of flight was ZZZZZ1; RNAV SID from ZZZ1; to ZZZZZ2 for forecast thunderstorm development. Dispatcher annotated on the Flight Plan/Release; that "direct routing may be available after departure." Based upon the northeasterly movement of the surrounding weather; ZZZ1 Center had us proceed behind; west; the majority of the convective activity and cleared us direct ZZZ [VOR] before reaching ZZZZZ1 on the SID. I think the flight crew; Dispatcher; and ATC properly managed the probable risks for the flight. Once we encountered the turbulence; we had few options but to continue to fly through it. The onset of the event happened so fast and was experienced so briefly; that other options for prevention were not available."
Second reporter narrative
While encountering to ZZZ [VOR]; ATC told us about some convective weather ahead. We chose to make a 10-degree left deviation in order to avoid it. This put us on a heading of 180 that would keep us further than 20 NM from both convective weather events. Once past the weather cells; ATC cleared us direct to ZZZZZ intersection and to cross 70 NM north of ZZZZZ at FL280. We began to descend to FL280 at 280 KIAS in LVL CHG. During the descent; close to level-off at FL280; we encountered severe turbulence. The turbulence lasted around 30 seconds. I watched the VSI go from a 2000 FPM descent and abruptly change to a 500 FPM climb. At that time the ATS (Autothrottle System) LEVER and Yaw Damper #2 and the Autopilot #2 turned off and we got a yellow hydraulic system LO PR ECAM message. We notified ATC of the severe turbulence event and told them there were no injuries or suspected aircraft damage.Cause: Weather/turbulence. Routing was good for flight. The weather/turbulence event was abrupt and couldn't be recognized before it happened. We continued to fly through it once it happened because there were no other options.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.