On April 1, 2002, about 2005 eastern standard time, a Boeing 747-400, G-BNLS, operated by British Airways as flight 214, was not damaged when it encountered turbulence shortly after takeoff from Boston/General Edward Lawrence Logan International Airport (BOS), Boston Massachusetts. The 2 certificated airline transport pilots, 15 flight attendants, and 196 passengers were not injured. One passenger sustained serious injuries. Visual meteorological conditions (VMC) prevailed and an instrument flight rules (IFR) flight plan was filed for the flight destined for London-Heathrow Airport (LHR), London, England. The scheduled international passenger flight was conducted under 14 CFR Part 129. In a written statement, the flight crew reported that 20 minutes after departure they encountered "moderate turbulence" while climbing through flight level (FL) 350, to their assigned altitude of FL 370. Several minutes later, they requested a descent from air traffic control to FL 330 to maneuver around the turbulence. During the descent, a flight attendant informed the flight crew that a passenger fell during the turbulence encounter and broke her right ankle. The flight crew then initiated a return to Boston, and landed without further incident. After landing, the passenger was transported to the hospital and the airplane was inspected for damage. When no damage was observed, the flight departed again at 2214, and continued to London uneventfully. The flight crew reported that windshear advisories had been issued at Boston prior to their departure; however, no turbulence was forecasted for their route of flight. The seat belt sign was illuminated for the entire fight. According to flight attendant interviews conducted by British Airways, the flight conditions were described as "fairly smooth" and the seat belt sign was illuminated as they prepared for the in-flight service. About 20-30 minutes into the flight, the airplane "shook briefly" and experienced a "sudden jolt." During the encounter, a passenger from seat 17J was returning to her seat from the lavatory, when she fell and was injured. A flight attendant administered first aid to the passenger and notified the flight crew of the injury. The flight crew then informed the flight attendants and passengers that the flight would be returning to Boston. The weather reported at Boston, at 1954, included wind from 270 degrees at 18 knots, gusting to 31 knots, 10 miles visibility, clear skies, temperature 8 degrees Celsius, dewpoint -3 degrees Celsius, and altimeter setting 29.80 in Hg.