Boeing 717-200 N994AT accident near Inverness, Florida

Probable cause

The flight crew's encounter with convective turbulence. Contributing to the accident was the failure of the operator's dispatch department to provide the flightcrew with current adverse weather information along the planned route of flight. Also contributing was the failure of the flightcrew to provide relevant forecast information to the cabin crew, and their failure to detect and avoid the existing convective conditions.

NTSB analysis

The scheduled passenger flight was climbing through 25,000 feet when it encountered convective turbulence in daytime instrument meteorological conditions. A flight attendant, who was servicing the aft cabin, sustained leg and ankle fractures when her service cart became airborne and struck her in the leg. Both the flight and cabin crew members stated that the turbulence was unexpected. The National Weather Service (NWS) had issued multiple, sequential warnings of significant meteorological activity (SIGMETs) regarding the potential for thunderstorms and turbulence along the flight's planned route. The operator's dispatch department provided the flightcrew with a SIGMET that was valid until about one hour before the scheduled departure time. Contrary to operator and regulatory requirements, the dispatch department did not provide the flight crew with updated, current information, which included two new SIGMETs, one of which was issued an hour before the scheduled departure time, and all of which were similar in content and coverage area. The flight crew did not check with dispatch to determine whether any SIGMETS were current for the planned departure time. None of the air traffic controllers who handled the flight prior to the event relayed any hazardous weather information to the flight, despite their requirement to do so.

Correlation of meteorological and flight path data indicated that the turbulence encounter occurred when the airplane penetrated a continuous line of thunderstorms that was present in the SIGMET coverage area. Strong radar echoes, indicative of potential turbulence, were detected below the airplane's altitude by ground-based weather radar. Review of the operator's flight and cabin crew guidance revealed that the procedures incorporated some of the latest industry strategies for mitigating turbulence hazards, but did not provide the flight attendants with the recommended level of autonomy when it came to decisions about when to provide service, or how to prioritize tasks, in the event of turbulence. Although hindered by the failure of the dispatch department to provide them with current SIGMETs, given the previous SIGMET and forecast for significant thunderstorms along the route, and atmospheric activity that was likely readily detectable by the airplane's onboard weather radar, the flightcrew could have anticipated the turbulence, and the flight attendants could have either been instructed to remain seated, or been provided with sufficient information to decide on their own, until the airplane was clear of the hazard area.

Text from the NTSB. Open the NTSB docket for ERA09LA488 for the full record.