Incident Overview
On April 29, 2010, at 2140 central daylight time, a Boeing 767-223 (registration N320AA) operated by American Airlines as flight 20 encountered moderate turbulence during cruise flight near Fort Dodge, Iowa. The flight was a scheduled domestic passenger service under 14 CFR Part 121, departing from San Francisco International Airport, California, and en route to John F. Kennedy International Airport, New York. Visual meteorological conditions prevailed at the time of the event. The flight subsequently diverted to Chicago O'Hare International Airport, Illinois, and landed without further incident.
Crew Reports
The captain stated that the seat belt sign had been illuminated for approximately 20 minutes, and flight attendants were instructed to secure the cabin and take their seats 10 to 15 minutes before the turbulence was encountered. The turbulence lasted for 3 to 5 seconds while the aircraft was deviating upwind around and over a buildup. The first officer reported that the seat belt sign had been on for "some" time; there had been light chop but no reports of moderate chop or turbulence. The turbulence occurred while on an upwind vector around a thunderstorm. After the encounter, the first officer was informed that one flight attendant had injured an ankle and another had injured a hip.
Flight Attendant Accounts
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, throwing the flight attendants off balance. A sound during the roll was perceived as 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, standing next to the number three flight attendant, hit the ceiling and then the floor with another flight attendant. The number three flight attendant believed she fractured her foot when she landed on the number eight flight attendant.
Flight Data Recorder Information
According to the flight data recording, the airplane was at an altitude of approximately 41,000 feet at an airspeed of about 232 knots with the autopilot engaged. During the event, vertical accelerations fluctuated between -0.5 and 2 g's, longitudinal accelerations between -0.1 and 0.1 g's, and 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 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 from 270 mb to 300 mb. Wind direction changed approximately 20 degrees further left, but this could be accounted for by a 20-degree rightward change in aircraft heading before the event.
Injuries and Occupants
Of the 178 people aboard, one flight attendant sustained serious injuries, two flight attendants sustained minor injuries, and three passengers sustained minor injuries.
Cockpit Voice Recorder
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.