On April 9, 2001, about 2200 eastern daylight time, a Dornier 328-100, N423JS, operated by PSA Airlines Inc., as flight 4110, was not damaged during an encounter with turbulence near Springfield, Virginia. The two flight crewmembers and 11 passengers were not injured; however, a flight attendant was seriously injured. Visual meteorological conditions prevailed and an instrument flight rules flight plan was filed for the flight destined for the Ronald Reagan Washington National Airport (DCA), Washington, District of Columbia, from Charleston International Airport (CHS), Charleston, South Carolina. The scheduled passenger flight was conducted under 14 CFR Part 121. According to the captain, as the flight approached the Richmond, Virginia area, it became evident that some convective activity had developed in the Washington, D.C. area. The flight crew attempted to establish communication with company facilities to obtain weather and landing field updates, but was not successful. The first officer contacted the flight attendant and advised her that there were thunderstorms in the DCA area, and she should secure the cabin due to possible encounters with turbulence. About 12 miles south of DCA, while descending through 4,000 feet, the airplane encountered "moderate or greater chop (rapid bumps or jolts without appreciable changes in altitude or attitude)." Due to the turbulence, the captain elected to divert the flight to the Richmond International Airport, Richmond, Virginia. The flight landed uneventfully and the crew was then asked by Air Traffic Control to remain parked on a taxiway, to await an open gate. While waiting, the first officer proceeded back to the cabin area to check on the passengers and flight attendant. The flight attendant stated to the first officer that she had been injured during the turbulence encounter, but was not incapacitated, and could continue to perform her duties. Ground paramedics were then notified and met the airplane at the gate. A physician evaluated the flight attendant's injuries and determined that she had fractured her scapula. After the accident, the flight attendant stated to a fellow employee that she was facing the galley and had her arm risen to lock the cup cabinet when the airplane encountered the turbulence. The flight attendant was then thrown into the galley door and fell to the floor. The airplane encountered additional turbulence and the flight attendant was thrown into the lavatory wall and back onto the floor, before proceeding to a passenger seat. The weather recorded at DCA, at 2200 was, winds from 320 at 17 knots, gusts to 22 knots, decreasing thunderstorms, scattered cumulonimbus clouds at 4,200 feet, a broken cloud layer at 9,500 feet, and an overcast layer of clouds at 11,000 feet.