Air carrier flight crew reported temporary loss of control and injuries to flight attendants due to severe turbulence.
Synopsis
Air carrier flight crew reported temporary loss of control and injuries to flight attendants due to severe turbulence.
Narrative
We were at cruise at an altitude of 370. We had briefed the flight attendants of light-moderate turbulence in the area for the next twenty mins. We turned the seat belt sign on and briefed the passengers of possible rough air. We had the radar on and reviewed WSI (Weather Stress Index). We believed that we had passed the weather and were heading on course. We were in IMC conditions with no cells depicted on the radar. The flight was smoothing out; when we heard some noise that sounded like static or possible light hail. We then hit severe turbulence causing us to bank to the right; and loose 1500 feet; our airspeed decreased and caused momentary stick shaker followed by rapid increase in speed and climb. The auto pilot was turned off climb stopped; the turn was continued to take us further south of the weather where we knew clear skies should be. During the turbulence two flight attendants were in the aisle and were thrown to the floor. They remained there till they felt safe to get in their seats. The event was less than a minute. We called and checked on crew and passengers; initially we were told that everyone was seated safe and no injuries. A few minutes later the flight attendants called and reported the FA C hit her back on an armrest and would like to have medical attention on arrival in ZZZ. ATC was advised of severe turbulence and moderate hail location. The same info was passed to dispatch via ACARS. We called ZZZ OPS to ask for medical. We continued to ZZZ without further incident. Upon arrival we were notified that our FA D had injured her right leg in the fall and would like to be checked out by medical team. We made an entry in the AML (Aircraft Maintenance Logbook) for sever turbulence and moderate hail.We believed that we had checked all weather and resources to find the best ride. I'm not sure of any way of avoiding this incident. The only takeaway I have is to request all FA's and passengers to be in seats with seat belts on if there is a chance of moderate turbulence.
Second reporter narrative
Severe turbulence was encountered at FL370 ZZZ; in IMC while deviating south for projected thunderstorms along our route of flight. Weather radar was used and no weather cells were depicted immediately prior to the event. Fasten Belts sign was illuminated; a PA had been made and the flight attendants were advised of light to moderate turbulence expected for the next 20 minutes. A sound like static discharge was initially heard which then increased in volume and we discussed may have been hail. Immediately upon this conclusion we experienced an uncommanded right wing down; stick shaker actuation and a significant negative VSI (Vertical Speed Indicator) followed abruptly by an increasing airspeed and a climb causing altitude deviations both above and below assigned altitude. We turned further south; were quickly in VMC and regained stable flight. When the aircraft was under control I as PM advised ATC of the encounter and provided information while the CA ensured no injuries to the FA's or Passengers. We were informed of no injuries and could assess no known damage to the aircraft. Approximately 10-15 minutes post the event; FA C advised of back pain associated with falling into a seat. I coordinated medical to meet the aircraft via ACARS and called the ZZZ1 Ops frequency while around 80 miles out. Upon landing the EMT's met the aircraft and took FA C to the hospital. As the passengers completed deplaning FA D realized a large contusion and also requested medical attention. EMT's determined FA D also should go to the hospital. CA called the duty pilot and talked with a ZZZ2 Chief. A logbook entry was entered for both the severe turbulence event as well as the Hail encounter. I did not see any visible damage to the aircraft while on the ground. Severe weather encountered with no depictions on weather radar.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.