NTSB Factual Report

On July 11, 2005, about 1900 eastern daylight time, Delta Air Lines flight 952, a Boeing 767-232, N113DA, experienced moderate turbulence, about 20 nautical miles northeast of Charlotte, North Carolina, while in cruise at FL370, and diverted to Raleigh-Durham International Airport (RDU), Morrisville, North Carolina. Of the 179 passengers and 8 crewmembers onboard, a passenger and some flight attendants received minor injuries, and one flight attendant received serious injuries. The flight was operating under the provisions of Title 14 CFR Part 121, and was en route from Hartsfield-Jackson Atlanta International Airport (ATL), Atlanta, Georgia, to La Guardia Airport (LGA), Flushing, New York.

The captain stated that his flight was the last aircraft to depart to the northeast, after which FAA Air Traffic Control (ATC) ceased all northeast departures. He further stated that he had left the fasten seatbelt light lit for about 25 minutes, until we flew through a hole in the weather. There had only been occasional light turbulence, and a request for a "ride report" from ATC, resulted in a response stating that there had been no complaints.

The captain said that he waited until reaching FL370, and was well past the line of weather to turn off the seat belt light. The flight was smooth for about 10 to 15 minutes, and they were transiting in and out of cirrus clouds, with the weather radar being used to scan from the 160 to 40 mile range, and with absolutely nothing but ground clutter being noted. He said the flight encountered moderate turbulence for about 10 to 15 seconds just south of High Point, and he immediately made a public announcement (PA) for the flight attendants and passengers to sit down. He also asked the ATC controller if the ATC radar showed any weather, and the controller responded saying, "no, the only weather I see is well behind you." The captain said he then overheard a flight attendant make a PA announcement requesting a doctor, and he told the controller of a possible diversion to Raleigh-Durham (RDU) International Airport. About the same time he said a flight attendant advised the cockpit that a flight attendant had been injured. The captain then assessed the situation, the flight was diverted, and otherwise uneventful landing was made at RDU, where the flight attendant was evacuated from the airplane.

The first officer stated that the flight departed late, and that the Atlanta, Georgia, area was still feeling the effects of Hurricane Dennis, which had passed through the area the day before. There were off-and-on rain showers over the airport, along with moderate winds, but no weather presented itself that had been of concern for an immediate departure.

The first officer stated that preflight, start, taxi and the take-off were uneventful, and the flight was cleared direct to "AHN." As the flight progressed there was convective weather off the airplane's nose, and the controller told the flight crew that they could deviate left of course, as much as was necessary, and to proceed to "LIB" when able. The flight easily transited between the two cells, entered clear skies, and continued the climb to FL370, direct to LIB, in smooth air. The seat belt sign had been turned off, and according to the first officer, the captain continued searching the area with the weather radar. Although there were some intermittent high cirrus clouds, no weather was noted that would pose problems along the route of flight.

About 10 to15 minutes after level-off, the first officer said the airplane hit what he would call severe turbulence, and both he and the captain were tossed about in their seats. They were initially unable to either grab the flight controls, or turn on the seat belt sign, and after the initial big bump, the first officer said "he grabbed the controls (it was my leg), and followed through with the thrust levers and yoke." He said the autopilot did not disengage, and it absorbed the increase and following decrease in altitude, as well as the eventual 400-plus-foot altitude gain. According to the first officer, the turbulence lasted about ten to fifteen seconds. As soon as able the captain turned on the seat belt sign, made the PA announcement for everyone to sit down, and according to the first officer, they immediately heard the "A-Line make the announcement asking for a doctor on the airplane." He said that he and the captain immediately knew something was wrong, so the captain called back and spoke to the flight attendants. The first officer said he listened in on the conversation, and upon conclusion, the captain told him to keep flying the airplane while he went back to take a look. The first officer said he then called ATC and told them to standby that they may have to divert because they had hit turbulence and that one of the flight attendants may have been injured. While the captain was engaged in assessing the situation with the flight attendant, the first officer said he researched and found that Raleigh-Durham International Airport seemed to the best choice of places to divert, given its location and weather.

When the captain returned to the cockpit, he directed that the first officer continue flying the airplane, while he coordinated with flight control. The flight then diverted to RDU, and otherwise uneventful landing was made. Upon arrival at the gate in RDU, the flight attendant was taken off the aircraft, and after about two hours the flight proceeded on to LGA.

All flight attendants provided statements pertinent to the event that were consistent, and their statements are included in the docket. Of the six, one of the flight attendants stated that shortly after takeoff, the captain made a PA about weather in the area, saying that he would be leaving the seat belt sign on a little longer than normal. The flight attendant further stated that the captain turned the sign off relatively soon, and all the flight attendants then got up and began cabin service. The flight attendant said she was working in first class with another flight attendant, and as they were in the galley the flight attendant with whom she had partnered commented on the rough air. The other flight attendant was delivering trays of food, and that she was delivering drinks. As she walked down the left aisle with a tray of drinks, the flight attendant said that severe turbulence hit their airplane. The seat belt sign was not on, and she said she flew up in the air, landing on her lower back and buttocks, while the drinks flew into the air. Flight attendants working in the main cabin had the food carts in the aisle at row 10, and they all fell to the ground as well. The beverage cart was then unattended and appeared as if it might fall on the passengers, so the flight attendant said she stood up and pulled the cart to the first class galley, at that time that she saw another flight attendant on the ground, with what appeared to be a broken leg. Another flight attendant attended to the injured flight attendant, while a PA was made for a doctor. The flight attendant said she then briefed the captain, and the flight readily diverted to RDU, where the injured flight attendant was taken off the aircraft by emergency medical personnel. The flight later departed for LGA, and the flight attendant said that both during the flight and later, while in her hotel room, she experiencing severe lower back pain, …shooting down to my right foot. According to the flight attendant, the accident turbulence event had been the worst she had ever experienced in her career.

A second flight attendant stated that after takeoff the seatbelt sign had remained on due to rough air in the area, and that after the sign was turned off, flight attendants began beverage service, with two flight attendants serving on the right side of the cabin, leaving the accident flight attendant and herself on the left. She had just served beverages when they first experienced very light rough air, and as she began to serve another person to the immediate left, the turbulence began again, and this time the turbulence was really rough. The flight attendant said that at that time the accident flight attendant turned and looked at her, and began to shake her head, and in less than two seconds the airplane lost altitude. The flight attendant said she braced herself in the bulk head between first class and coach, and the airplane dropped again, with the accident flight attendant falling to the floor. The flight attendant said that passengers held on to her as she hastily sat in front of them, and moments later, another flight attendant came to the bulk head to check on her and assist in taking the beverage cart to the first class cabin, at which time they noticed that a flight attendant was seriously injured.

The injured flight attendant stated that the seat belt sign was off, and they had positioned the beverage and snack carts to the front of the coach cabin. She further stated that she was preparing to serve from the beverage cart on the captain's side of the airplane, and that she was feeling somewhat nervous during the moments prior to our encounter with the severe turbulence. She said it was bumpy in the cabin and everything seemed unusually quiet, with her having a feeling that something just didn't feel right. She hadn't yet served any passengers, and she asked a flight attendant, "Are we supposed to be up?" Immediately after having spoken those words, she said that they encountered turbulence, and the next thing she remembered was that she was on the floor in the aisle, looking at her injured leg.

The digital flight data recorder (DFDR) was sent to the NTSB's Recorder Laboratory, Washington DC, for readout. The DFDR was examined in the recorder laboratory and all pertinent parameters provided information was consistent with a turbulence event of about 40 seconds duration having occurred. The data showed that the airplane's autopilot had been engaged, and there was a lateral acceleration during the first vertical drop, without corresponding flight or engine control input, consistent with clear air turbulence. See the NTSB DFDR Factual Report.

The NTSB conducted a meteorological study, utilizing data which included surface observations, upper air sounding data, satellite imagery, radar data, and NWS forecasts. These weather products provided information pertinent to atmospheric conditions which existed at the time of the accident, and the information was consistent with there being convective induced turbulence in the vicinity of strong to severe thunderstorms.

Of the data that was examined, visible and infrared imagery satellite data was used, and the GOES-12 satellite imagery associated with the time of the accident flight indicated a band of cumulonimbus clouds embedded in a broken to overcast cloud layer extending over the Charlotte area and preceding to the accident location. Enhanced infrared satellite imagery confirmed convective activity in the vicinity of the accident location, and cloud tops were from 41,000 to 37,000 feet.

In addition, the NWS Columbia (KCAE), South Carolina, Weather Surveillance Radar-1988, Doppler (WSR-88D) indicated a multi-cellular line of convective cells at VIP Level 5 "intense echoes" at the lower scans extending northwest through northeast of the Charlotte area during the period of the accident. At altitude, the intensity decreased to VIP Level 2 "moderate" intensity, and although less intense, were still identifiable with that of a line of convection. See the NTSB Meteorological Factual Report.

NTSB Probable Cause

An inadvertent in-flight encounter with clear air turbulence.