What happened
While descending toward Detroit, the aircraft encountered a period of unsettled air. The captain had previously activated the seat belt sign and issued a passenger announcement regarding the potential for turbulence. The flight initially experienced light turbulence, which transitioned into moderate turbulence as the aircraft descended from 18,000 feet to 12,000 feet.
An off-duty flight attendant was walking through the cabin toward the lavatory when the encounter occurred. While returning to their seat in the exit row, the aircraft encountered a severe pocket of air without warning. The sudden dip caused the crew member to be lifted into the air and fall to the cabin floor, resulting in one broken ankle.
The investigation
A review of the flight data recorder was conducted to analyze the aircraft's movement during the descent. The data revealed that between altitudes of 14,429 feet and 11,114 feet, the vertical acceleration of the airplane fluctuated between .56 g's and 1.39 g's.