On June 7, 2012, at approximately 1600 coordinated universal time, US Airways flight 1078, a Boeing 757-200, N936UW, encountered turbulence during descent into Philadelphia International Airport (KPHL), Philadelphia, Pennsylvania. One flight attendant in the aft galley suffered a broken ankle and two other flight attendants suffered minor injuries. The other five crewmembers and 178 passengers were not injured and the airplane was not damaged. The flight was operating under the provisions of 14 CFR Part 121 as a regularly scheduled passenger flight from Luis Muñoz Marín International Airport (LRSM), San Juan, Puerto Rico, to KPHL. According to the operator, the flight crew weather briefing indicated no turbulence forecast for the route of flight. The departure, cruise, and initial descent portions of the flight were uneventful. The captain reportedly turned on the seatbelt sign when the flight was passing through flight level 180. About 50 miles outside of KPHL, the flight crew identified a small band of cumulus clouds between 13,000 feet and 9,000 feet. The captain made a public-address announcement to the passengers reminding them to have their seatbelts fastened and alerted them to the possibility of some minor turbulence as they passed through the clouds. Prior to descending through 10,000 feet, the flight encountered moderate turbulence for approximately 3-5 seconds. There were no pilot reports or advisories from air traffic control about turbulence in the area. When the turbulence was encountered, the D flight attendant (FA) was in the aft galley performing final landing preparations and was lifted into the air and thrown the floor near the last row of passenger seats. She was assisted by other FA's but remained on the floor for the remainder of the flight due to her injured leg. Paramedics met the airplane at the gate and transported the flight attendant to the hospital where she was diagnosed with fractures to her tibia and fibula.