Incident Overview
On August 27, 2009, at approximately 1603 eastern daylight time, AirTran Airways flight 163, a Boeing 717-200 (registration N994AT), encountered convective turbulence while climbing through flight level 250 near Inverness, Florida. The flight, operating under Title 14 CFR Part 121 as a scheduled passenger service, had departed Tampa International Airport (TPA) and was en route to Hartsfield-Jackson Atlanta International Airport (ATL). Instrument meteorological conditions prevailed, and an instrument flight rules flight plan had been filed.
Events Leading to the Turbulence Encounter
After departure, the flight crew reported that the airplane was assigned a heading of 350 degrees and cleared to climb to its cruise altitude. The airplane entered instrument meteorological conditions (IMC) and encountered "very mild light chop." No pilot reports of turbulence or cells were visible on the aircraft's radar. The seat belt sign was illuminated. As the airplane passed through 10,000 feet, the three flight attendants began cabin service. The captain and first officer were both at the controls; the non-flying pilot monitored the airborne radar but detected no weather cells.
Turbulence Encounter and Injuries
When the airplane reached flight level 250, still in IMC, it experienced turbulence lasting approximately 15 seconds. The flight data recorder indicated a rapid vertical acceleration increase to about 2.5 g, followed by a decrease to 0.5 g within one second, with subsequent fluctuations. During this period, the aircraft experienced pitch excursions of about 5 degrees, roll excursions of about 20 degrees, and an airspeed decrease of approximately 15 knots.
The lead flight attendant, who was in the galley at the front of the cabin, reported being lifted about a foot off the floor. The two other flight attendants (designated R1 and L2) were working a service cart in the rear aisle. During the turbulence, the L2 flight attendant and the cart came off the floor, and the cart struck her leg. After the turbulence subsided, the L2 flight attendant was found lying on the floor and complained of intense pain in her right leg. Her leg was immobilized, and a passenger who was a nurse assisted her to an unused row of seats. The flight crew was notified, and medical personnel met the flight in Atlanta. The injuries were later diagnosed as a fractured tibia and a crushed ankle. The remaining two flight attendants and the 81 passengers were not injured, and the airplane sustained no damage.
Meteorological Conditions
Meteorological data from the National Weather Service and radar imagery indicated conditions conducive to thunderstorm development in the region. Convective SIGMETs had been issued for the area, including SIGMET 43E (valid until 1655) and SIGMET 46E (issued at 1555, valid until 1755). Ground-based radar data showed that the airplane was penetrating a line of radar echoes at the time of the encounter, with reflectivity levels of 20-30 dBZ at the airplane's altitude and 50-55 dBZ below. Infrared satellite imagery from 1602 showed cumulus clouds with tops near 36,500 feet at the location. The operator later suggested the airplane encountered a "Tail-end Charlie"—a trailing cell in a line of thunderstorms.
Communications and Crew Actions
Review of air traffic control communications revealed that none of the four controllers who communicated with the flight prior to the encounter mentioned the active convective SIGMETs or broadcast a HIWAS alert. The flight crew did not advise the cabin crew to remain seated or provide information about anticipated turbulence. According to the flight crew, no preflight briefing regarding turbulence was documented. The lead flight attendant reported that only light turbulence had been experienced before the event.
Aircraft and Personnel Information
The Boeing 717-200, a variant of the DC-9, was manufactured in 2002 and powered by two Rolls-Royce BR715 turbofan engines. At the time, it had a gross weight of approximately 99,000 pounds and was configured for 2 flight crew, 4 cabin crew, and 117 passengers (though only three flight attendants were on board). The captain had 18,700 total flight hours, with 5,000 hours in the 717; the first officer had 10,000 total hours, with 3,000 hours in type. The injured flight attendant had been employed for 2.5 years; the lead flight attendant had nearly 5 years of service.
Operational Guidance
The operator's Flight Attendant Manual and Flight Operations Manual provided guidance on turbulence procedures. The manuals emphasized crew communication and stated that during light turbulence, normal cabin duties could be accomplished. For moderate or severe turbulence, flight attendants were to secure the cabin and take seats. However, the guidance did not require the flight crew to provide an estimate of time before anticipated turbulence. The Commercial Aviation Safety Team (CAST) and Joint Safety Analysis Team had previously identified turbulence as a principal cause of flight attendant injuries and recommended policies for flight attendants to remain seated during periods of significant turbulence risk.