On May 13, 2006, about 1600 eastern daylight time, a passenger was seriously injured when an Embrear 145LR, N653AE, operating as American Eagle flight 3967, encountered turbulence near Winchester, Virginia. Three crewmembers and 42 passengers were not injured, and there was no damage to the airplane. Instrument meteorological conditions prevailed. The flight was operating on an instrument flight rules flight plan between Chicago O'Hare International Airport (ORD), Chicago, Illinois, and Washington Dulles International Airport, Dulles, Virginia. The scheduled passenger flight was being operated under 14 CFR Part 121. According to the captain, the airplane was operating at 10,000 feet, near TRIXY intersection, and the seat belt sign had been illuminated for 10-15 minutes, when the crew noticed that clouds ahead "appeared bumpy." The flight attendant was notified, and she advised the passengers of possible turbulence via the public address system. A passenger subsequently got out of her seat to use the lavatory, and upon leaving the lavatory, while the airplane was in a cloud for about 20 seconds and experiencing turbulence, she fell and broke her ankle.