On June 15, 2001, about 1945 Pacific daylight time, a flight attendant sustained serious injuries on an Airbus Industrie A320-232 transport category airplane, N661AW, operating as America West flight number 186, while descending for an approach into San Diego, California. America West Airlines was operating the airplane under the provisions of 14 CFR Part 121. The airline transport pilot captain, airline transport pilot first officer, the remaining 2 flight attendants, and 137 passengers were not injured. The airplane was not damaged. The regularly scheduled domestic passenger flight departed Phoenix, Arizona, about 1900 mountain standard time as a nonstop flight to San Diego. Instrument meteorological conditions prevailed and an IFR flight plan had been filed. According to the flight safety office at America West, the flight was inbound to San Diego and descending through 13,000 feet near Pillo intersection when a flight attendant in the aft cabin fell and struck her head. According to the injured flight attendant, the flight crew initiated a sudden descent, which caused her to lose her balance and fall. The captain reported to the airline that air traffic control had held them at 13,000 feet for traffic reasons until just before they reached Pillo intersection, then cleared the flight to descend on the standard arrival route. Pillo intersection is about 39 miles from the airport. Captain Statement According to the captain's written statement, they were descending into San Diego via the Baret 4 arrival when they encountered moderate turbulence. The flight crew was later informed that the 2nd flight attendant "had fallen due to apparent dizziness." The flight crew then called ahead to have paramedics meet the airplane at the gate. First Officer Statement According to the first officer's written statement, during level off at 11,000 feet msl, the flight encountered light turbulence that "caused a momentary overspeed condition with appropriate aural/ECAM warnings. This disconnected the autopilot and would not allow it to reengage." The first officer advised the captain that the autopilot was disconnected and he started a manual level off. Once the airplane slowed, the flight crew reengaged the autopilot and landed without any further incidence. Following the turbulence encounter, the flight crew learned that the 2nd flight attendant fell and was injured during the turbulence event while she was standing near the overwing position. Flight Attendant Statement According to the flight attendant's written statement, she was in the cabin collecting trash prior to landing. When she was in the overwing area of the cabin she felt a "bump," but didn't think much of it. The airplane then "descended rapidly" and the flight attendant fell, hitting her head and back on something. She subsequently lost consciousness. When she awoke, she was assisted to a 1st class seat for the remainder of the flight. The following day, the first officer called the flight attendant to apologize, telling her they had to make an unannounced descent to make the landing air traffic control cleared them for. He added that they did not encounter turbulence.