Air carrier flight crew reported loss of aircraft control in cruise during severe turbulence encounter resulting in significant altitude and airspeed deviations. Flight crew regained control and continued flight.
Synopsis
Air carrier flight crew reported loss of aircraft control in cruise during severe turbulence encounter resulting in significant altitude and airspeed deviations. Flight crew regained control and continued flight.
Narrative
After deviating around weather west of the arrival and having the flight attendants prepare the cabin early and use moderate turbulence procedures; Approach Control vectored our flight towards BOOVE intersection and we requested 13000 to remain below a cloud deck that appeared to have virga and mammas cloud formations. We were given the descent and handed off to the next controller. As we checked in; numerous aircraft were giving PIREPS of continuous moderate and occasional severe turbulence. Soon after we heard this our aircraft encountered the moderate turbulence and we requested further descent to 11000. Once we were cleared to descend; the turbulence increased in intensity to the point the aircraft was uncontrollable in both pitch and roll. The Autopilot disconnected as the aircraft was unable to maintain altitude and our descent rapidly continued to around 10700 feet as I regained control of the aircraft and returned to 11000. We quickly called to the cabin to ascertain if they were any injuries or damage. Luckily; there were no injuries or damage and we proceeded to a normal approach and landing.Cause: ATC knew of reports of continuous moderate and severe turbulence reports ahead of us; yet they did nothing to stop the flow of traffic on the arrival.Suggestions: Better ATC communication between controllers.
Second reporter narrative
At top of climb on flight XXXX; the Captain and I checked our weather app and noticed multiple large thunderstorm cells with tops exceeding FL600 were starting to encroach on our STAR going into DFW. Over the next hour or so; we monitored the storms via the weather app and discussed various courses of action that we could take to mitigate adverse flight conditions associated with the degrading weather. We discussed going south of the thunderstorms and taking a north turn toward the airport. As the storms started to come into view; we confirmed that the tops; indeed; had exceeded FL600; indicating a severe super cell thunderstorm. The Captain and myself discussed how we both respected the strength of such storms and decided; as a crew; to keep as far away from the cells as we saw fit. ATC then gave us direct San Angelo VOR and then direct to another fix on the arrival. On the radar this looked like a good course and we accepted the clearance. As we were ready to turn north toward the airport; the downwind side of the super cell had multiple blow-off and overhang clouds that appeared very ominous. The Captain and I did not want to get close to these and requested further right deviations and to descend to a lower altitude to avoid them. As we were flying under the overhangs; I noticed that mammatus clouds were present above us. Seeing this; I told the Captain that we are likely going to get a rough ride heading into DFW. He agreed and I gave an announcement to the passengers to expect bumps heading into DFW. As we continued; we were level at 13;000; we noticed scud-like clouds that were even with our altitude just up ahead. We asked for lower and ATC gave us 12;000. I then called the FA's 'All call' and told them to remain seated and proceed with 'moderate turbulence' procedures. About 60 seconds later we hit very strong moderate chop and reported it to ATC. The aircraft ahead of us needed to descend even further to 11;000 and we requested the same. Upon reaching 11;000; the aircraft leveled out momentarily. After doing so; we hit severe turbulence under the overhang cloud. The aircraft was uncontrollable for a duration of 10-15 seconds. The Autopilot disconnected and we were unable to maintain altitude. I reported to ATC that we were encountering severe turbulence and we were unable to maintain altitude. The Captain; at this moment; was hand flying the aircraft to avoid further upset. He did so very well. We were able to re-establish automation as we regained aircraft control. In all; we lost roughly 500-700 ft of altitude and 30-40 knots of airspeed. As aircraft control was regained; I called the flight attendants (FAs) to see if they and the passengers were okay. Thankfully they were. We continued the approach and landing in constant moderate turbulence and landed without further incident. Cause: Severe thunderstorms avoidance is something that played a role in this event. The Captain and myself had very solid CRM and communication. We stayed as far away from the storms as we saw fit. This turbulence occurred at least 35-45 miles from any precipitation. The turbulence was caused by overhang and scud clouds very far from the associated towering cumulonimbus. The storm we avoided was very strong and easily one of the largest I have seen in my career. I felt we stayed far enough from the storm to avoid any adverse conditions; but the overhangs and scuds was nothing like I had seen before. Air traffic control did not provide any ride reports or give us any indication that aircraft in front of us had experienced anything adverse. As we reported moderate and later severe turbulence; their response was 'yeah its gonna be bumpy; dont know what to tell you.' Almost as if we were inconveniencing them. We also knew we had some company traffic behind doing the same and we requested that aircraft not be sent through our route. Their response was 'we'll see what we can do' Suggestions: Air traffic control should have given us a betterheads up concerning turbulence; as we were not the first ones reporting it. No one reported severe; but they were multiple reports of moderate. I only gave the flight attendants a warning because I did not like how the clouds in our flight path looked and expected a very rough ride.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.