FTW00LA244

During cruise flight at 37,000 feet over the Gulf of Mexico, the scheduled international passenger flight encountered severe turbulence after inadvertently penetrating rapidly developing convective formations. One of the flight attendants was seriously injured. When the turbulence encounter occurred, the flight crew was attempting to deviate around cloud formations. The flight crew reported that the seat belt sign was illuminated prior to the turbulence encounter and that the captain made an announcement to the passengers reminding them to remain seated with their seatbelts secured. It is unknown whether the flight attendant was seated or standing, or where she was positioned at the time of the event. Following the turbulence encounter, the flight diverted to a nearby airport and landed without further incident.

On August 23, 2000, at 1457 central daylight time, a Boeing 757-223, N657AM, operating as American Airlines flight 304, encountered severe turbulence during cruise flight at 37,000 feet mean sea level over the Gulf of Mexico, approximately 180 nautical miles southeast of the Sabine Pass VORTAC. There were 60 passengers, 2 flightcrew members, and 6 flight attendants aboard the airplane. One flight attendant was seriously injured, and 4 flight attendants and 8 passengers sustained minor injuries. The airplane received minor damage to the cabin interior. The scheduled passenger flight was operating under 14 Code of Federal Regulations Part 121. Flight 304 departed the Dallas/Fort Worth International Airport and was en route to San Juan, Puerto Rico. An instrument flight rules flight plan was filed and the airplane was operating in instrument meteorological conditions at the time of the accident. Following the turbulence encounter, the flight diverted to the George Bush Intercontinental Airport in Houston, Texas, and landed without further incident at 1543.

According to a written statement provided by American Airlines' Manager of Flight Operations Safety, the flight was in the vicinity of KELPP intersection and the flight crew requested an "easterly (left) deviation" from air traffic control (ATC) to avoid possible convective activity. The flight crew "chose this [deviation] in order to remain on the upwind side of the weather activity." Prior to their request for a deviation, "the captain made an assertive announcement to the passengers reminding them that the seat belt sign was on and to remain in their seats with their seat belts fastened." As the flight deviated off-course, the airplane "entered a layer of stratus" clouds. The on-board weather radar equipment continued to "display the convective activity to the right of their flight path." As the airplane exited the stratus layer of clouds, "a cloud formation that was not painting on the radar appeared in front of the aircraft's flight path." The captain "took immediate action to avoid the cloud" by using the maximum bank angle allowed by the autopilot. While maneuvering to avoid the cloud formation, the flight encountered "moderate turbulence followed by an updraft and then approximately 4-5 seconds of severe turbulence."

After the turbulence event, a flight attendant notified the pilots that one of the flight attendants and one or more passengers had sustained possible injuries. The captain declared a medical emergency and requested a diversion to Houston. The remainder of the flight and landing were uneventful.

According to the operator, one of the flight attendants sustained a "cracked #7 vertebrae." Written statements provided by the flight attendants indicated that they were serving meals to the passengers, and the seriously injured attendant was in the aft galley area at the time of the turbulence encounter.

Official ATC communication transcripts confirmed that the flight crew of flight 304 requested a deviation at 1549:43, over KELPP due to weather. At 1552:05, flight 304 indicated that they were going to fly "seven miles left of course for weather that is to the east." At 1557:47, flight 304 informed ATC that they had encountered "severe turbulence."

Review of the flight data recorder (FDR) information indicated that the turbulence encounter occurred at 1556:25, and lasted approximately 20 seconds. The peak vertical accelerations sustained by the aircraft were +1.45 and -0.88 G's. At 1556:39, the altitude alert sounded when the flight deviated to 37,390 feet. The autopilot was engaged at the time the aircraft encountered the turbulence.

An NTSB meteorologist reviewed Geostationary Operational Environmental Satellite (GOES) visible and infrared data. GOES images for 1545 and 1615 depicted a short line of convective clouds oriented east-northeast/west-southwest along the route of flight. The NTSB meteorologist also reviewed Dopplar weather radar data from Houston between 1548:37 and 1608:32. That radar data revealed that reflectivity returns were present in the vicinity of the turbulence encounter area for the period surrounding the accident. The data also depicted increased reflectivity values and convective echoes throughout that period, which is indicative of rapid convective development. There were two in-flight weather advisories issued for the Gulf of Mexico coastal areas; however, flight 304's ground track passed well beyond those advisory areas at the time of the turbulence encounter.