On May 16, 2011, at about 1830 eastern daylight time, Pinnacle Airlines flight 3621, a DHC-8-402, N351NG, encountered severe turbulence while descending through about 14,000 feet while on initial approach to Ronald Regan National Airport (KDCA), Washington, District of Columbia. One flight attendant received a serious injury and the airplane was not damaged. The flight was operating under 14 CFR Part 121 as a regularly scheduled passenger flight from Newark International Airport (KEWR), Newark, New Jersey to KDCA. According to the operator, the flight crew had not received any PIREPS or NOTAMS of forecasted turbulence and the flight attendants (FAs) had just stowed the galley service carts when the turbulence was encountered. One FA was thrown to the floor injuring her foot. The flight attendant was assisted to a passenger seat where ice was administered to her swollen foot. Paramedics met the flight upon landing and transported the injured flight attendant to the hospital where she was diagnosed with a fracture in her right foot.