A Compass Airlines Embraer ERJ-175 on behalf of Delta Airlines, registration N637CZ performing flight CP-5774/DL-5774 from Salt Lake City,UT (USA) to Calgary,AB (Canada) with 73 people on board, had been enroute at FL300 and was in the initial descent towards Calgary when the crew reported a flight attendant had been injured by turbulence. The aircraft continued for a safe landing in Calgary.
The FAA reported the aircraft enountered "mountain turbulence", a flight attendant received a back injury, the occurrence was rated an accident.
On Aug 6th 2019 (more than a year later) the NTSB reported they have opened an investigation into the occurrence rated an accident, that occurred near Cut Bank,MT (USA). The NTSB stated: "NTSB investigators will use data provided by various entities, including, but not limited to, the Federal Aviation Administration and/or the operator, and will not travel in support of this investigation to prepare this aircraft accident report."
On Jul 12th 2020 the NTSB released their final report concluding the probable cause of the accident was:
an unexpected encounter with clear air turbulence.
The NTSB reported one flight attendant received serious injuries and wrote: "According to the flight crew, air traffic control (ATC) relayed pilot reports of a 'smooth ride with light chop' for their route of flight. The airplane was in visual meteorological conditions and the seatbelt sign was illuminated. At the time of the turbulence encounter the aft flight attendant was finishing up beverage service and was thrown against the bulkhead and jumpseat. The flight attendant was unable to complete her duties due to the injury and two passengers assisted the flight attendant until landing. Upon arrival at the gate in CYYZ, the flight attendant was transported to the hospital where she was diagnosed with a broken vertebra."