On April 29, 2010, at 2140 central daylight time, a Boeing 767-223, N320AA, operated by American Airlines as flight 20, encountered turbulence during cruise flight near Fort Dodge (FOD), Iowa. Visual meteorological conditions prevailed at the time of the accident. Of the 178 people aboard, 1 flight attendant sustained serious injuries, 2 flight attendants sustained minor injuries, and 3 passengers sustained minor injuries. The 14 CFR Part 121 scheduled domestic passenger flight departed San Francisco International Airport, San Francisco, California, and was en route to John F. Kennedy International Airport, New York, New York. The flight diverted to Chicago O'Hare International Airport, Chicago, Illinois, and landed without further incident.

The captain stated that the seat belt sign was on for about 20 minutes, and the flight attendants were instructed to secure the cabin and to take a seat 10-15 minutes prior to when they encountered moderate turbulence. The turbulence lasted for 3-5 seconds in the area of FOD while deviating upwind around and over a build-up.

The first officer reported that the seatbelt sign was on and had been on for “some” time. There had been light chop but no reports of moderate chop or turbulence. They encountered moderate turbulence when they were on an upwind vector around a thunderstorm. After the turbulence encounter, the first officer received a report that one flight attendant injured her ankle and another flight attendant injured his hip.

The number three flight attendant was standing aft looking into the main cabin after food service had just been completed when the airplane banked to the left and threw the flight attendants off balance. There was a sound during the roll of either wind or an engine. The airplane then seemed to move back to the right, but dropped while completing its level off. The number eight flight attendant, who was standing next to the number three flight attendant, hit the ceiling and then the floor with another flight attendant. The number three flight attendant thought she fractured her foot when she landed on the number eight flight attendant.

According to the flight data recording for the flight, the airplane was at an altitude of approximately 41,000 feet at an airspeed of approximately 232 knots with the autopilot engaged. At the time of the event, the vertical accelerations fluctuated between -0.5 and 2 g’s, the longitudinal accelerations were between -0.1 and 0.1 g’s, and the lateral accelerations spiked as high as 0.2 g’s and as low as -0.1 g’s. The airplane rose and fell approximately 100 feet in each direction and the airplane rolled as far right as 20 degrees.

There was no sudden change in wind direction or air pressure before the event. During the event, total air pressure spiked up to 300 mb from 270 mb. Wind direction changed to approximately 20 degrees further left during the event, but that can be accounted for by aircraft heading, which changed 20 degrees to the right before the event.

The cockpit voice recorder was reported as not having been deactivated following the accident and no recording for the accident flight was available to the National Transportation Safety Board.