What happened
The flight had been experiencing moderate chop for a period during its initial descent. For approximately 20 minutes prior to the event, the cabin seat belt sign had been illuminated, and all passengers were secured in their seats. At the time of the incident, the cabin crew had finished beverage service and were in the process of stowing galley equipment.
As the aircraft descended through 17,500 feet, it encountered a single severe turbulence jolt. Two cabin crew members were standing in the aft galley during this encounter. One crew member managed to grab a hand hold, but the second was thrown against the ceiling and then back to the floor.
The impact resulted in two injuries. The attendant who struck the ceiling sustained a compound fracture of an ankle that required surgical repair. The second attendant received treatment at a hospital for soft tissue injuries and was subsequently released.
The investigation
An examination of weather reports revealed that SIGMET Papa 13 had been issued at 221656, forecasting moderate to occasional severe turbulence in southern California below 18,000 feet. Additionally, Center weather advisories 01 and 02 were active for the area and time, predicting moderate to occasional severe turbulence below 22,000 feet.
A review of the dispatch weather package provided to the flight crew in Chicago showed the package was prepared at 221501. This preparation time occurred prior to the issuance of both SIGMET Papa 13 and the two center weather advisories. No SIGMETs were identified for the terminal portions of the flight.