History of Flight
On October 26, 2009, at approximately 1202 eastern daylight time, AirTran Airways flight 669, a Boeing 717-200 (registration N935AT), was in cruise-descent near Pleasant Grove, North Carolina. The aircraft was not damaged. The crew consisted of 2 pilots, 2 flight attendants, and 116 passengers. One flight attendant received serious injuries, and one passenger received minor injuries; no other injuries were reported. Visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed. The flight originated from Orlando International Airport (MCO), Florida, and was destined for Westchester County Airport (HPN), New York.
At 1220, the operations center received an ACARS message from the flight crew stating that a flight attendant had fallen and a boy had a "bump on head." The crew reported they were descending from flight level (FL) 350 to 330 due to turbulence and halted their descent for a resolution advisory (RA) from the traffic alert and collision avoidance system (TCAS).
According to the cabin crew, about one hour into the flight, the captain made a public address announcement about turbulence. Within seconds, one flight attendant in the forward galley was thrown into the counter, and another in the front cabin came up slightly from her jumpseat. It appeared to both that the airplane had dropped several hundred feet.
Passengers were seated except for a 10-year-old boy exiting an aft lavatory. A flight attendant returning to her jumpseat noticed the boy and waited to be seated. At that time, she and the boy were tossed to the ceiling and then back to the floor. Passengers rang call buttons, and the other flight attendants found the injured flight attendant and the boy on the floor. The boy was crying and had a "knot" on his upper forehead and knees; the flight attendant may have briefly lost consciousness and was "stiff and hurting." An eye doctor and retired paramedic assisted, applying an ice pack to the boy's head and helping the flight attendant to a seat with Aleve.
Paramedics met the flight at HPN; the flight attendant and child were transported to a local hospital. The flight attendant was admitted and remained under a doctor's care for more than 48 hours.
The captain reported cruising about 100 miles south-southeast of Kinston, North Carolina, in instrument meteorological conditions at FL350 in continuous light chop with the seat belt sign off. The chop intensified with a couple of moderate bumps, then became constant with periodic larger bumps. The captain turned on the seat belt sign, asked the first officer to query ATC for ride reports, and requested a descent. ATC cleared them to FL330. During the descent, after handing control to the first officer, the captain made a PA announcement. During the announcement, TCAS annunciated "TRAFFIC." The captain saw a red square on the primary flight display at the 1 o'clock position. He disconnected the autopilot and arrested the descent. Another "TRAFFIC" annunciation occurred, then "MONITOR VERTICAL SPEED." They exited the cloud layer and the captain observed a Boeing 737 or similar aircraft pass below to his right. He leveled at FL330, reengaged autopilot, and continued. He did not recall a traffic advisory from ATC.
Flight Crew Information
The captain held an airline transport certificate with type rating for the aircraft, with 9,145 total flight hours. His most recent first-class medical was September 17, 2009. The first officer held an airline transport certificate with type rating, with 8,360 total flight hours. His most recent first-class medical was March 5, 2009.
Aircraft Information
The Boeing 717-200 (N935AT) was a twin-engine, single-aisle aircraft equipped with electronic flight instrumentation, dual flight management system, central fault display, GPS, and TCAS. It was powered by two Rolls-Royce BR-700-715C1-30 turbofan engines. Manufactured in 2000, its most recent continuous airworthiness inspection was September 4, 2009. Total flight hours at the time were 23,031.
Meteorological Information
A weather observation at Norfolk International Airport (ORF) about 31 minutes after the event recorded wind 070° at 11 knots gusting to 17 knots, visibility 10 miles, broken clouds at 12,000 feet, temperature 16°C, dew point 9°C, altimeter 30.23 inHg.
Flight Recorder Data
FDR data from N935AT showed 27 hours 9 minutes of data; the accident flight was the 7th of 15. During cruise descent, a TCAS resolution advisory occurred, followed 1.5 seconds later by a positive vertical acceleration of about 1.6 g. One second later, a negative acceleration of about 0.2 g, then another positive load of 1.4 g, after which the acceleration dampened.
TCAS System and Guidance
TCAS builds a three-dimensional map of aircraft and determines collision threats. It automatically negotiates avoidance maneuvers. Manufacturer guidance states crews should "promptly but smoothly" follow an RA and never maneuver in the opposite direction. On the Boeing 717, the RA is incorporated into the vertical speed tape with red or green bars. Typical RAs require crew response within 5 seconds and G-forces of ±0.25G.
Operator guidance for the Boeing 717 at the time did not include specific TCAS RA response procedures; however, revision 29 of the Boeing 717 Aircraft Operations Manual, published August 20, 2010, added that information.