19961222039619A

Encountered severe turbulence while descending to airport. (.4)the flight had been in moderate chop for some time during the initial descent. The cabin seat belt sign had been illuminated for about 20 minutes and all passengers were secure in their seats. The cabin crew had just completed a beverage service and were stowing galley equipment at the time. As the aircraft was descending through 17,500 feet one severe turbulence jolt was experienced. The injured cabin crew members were standing in the aft galley; one was able to grab a hand hold while the other one was thrown against the ceiling and back to the floor. The cabin attendant who was thrown to the ceiling sustained a compound fracture of one ankle, which required surgery to repair. The second cabin attendant was treated at the hospital for soft tissue injuries and released. Review of the weather reports disclosed that SIGMET papa 13 was issued at 221656 and forecast moderate to occasional severe turbulence in the southern portions of California below 18,000 feet. Center weather advisories 01 and 02 were in effect for the time and location of the encounter and predicted moderate to occasional severe t urbulence below 22,000 feet. The dispatch weather package provided to the flight crew at chicago was reviewed. The date/time group for the package preparation was noted to be 221501, prior to the issuance of sigment papa 13 and both center weather advisories. No sigmets were noted for the terminal portions of the flight.