N173UA
BOEING 747-422
The flight crew reported a normal takeoff and climbout with a small amount of clouds and rain in the area. The preflight weather briefing package included a forecast of convective activity including a SIGMET (significant meteorological information) for thunderstorms south of the Beijing area moving northeastward. The crew was aware of the potential for convective activity during the climbout from Beijing, and the initial enroute segment over the Bohai Sea. During flight, the Captain was actively using the airborne weather radar to search for convective returns, including using the Doppler functions. Satellite imagery showed a signature termed “transverse banding” which is indicative of thunderstorms and turbulence at altitude. Based on the lack of weather radar returns, the Captain kept the cabin seat belt sign illuminated, but advised the cabin crew that they could begin service. The airplane encountered convectively induced turbulence, resulting in a peak vertical acceleration of over 2 G’s. The activity was likely developing upwards into the flight path, and precipitation attenuation and/or radar over-scanning may have contributed to the lack of visibility of the condition, which led to the risk assessment to allow the flight attendants to begin service. Following the turbulence encounter, the flight crew controlled the airplane appropriately to avoid an overspeed or other hazardous condition. The flight and cabin crew consulted with a physician passenger and determined continuing the flight per the injured flight attendant’s desire, was appropriate.
HISTORY OF FLIGHT On July 29, 2011, at 0558 Universal Coordinated Time (UTC) a Boeing 747-422, registration N173UA, operated by United Airlines as flight 888, encountered turbulence resulting in serious injuries to a flight attendant during climbout from the Beijing International Airport, People’s Republic of China (PEK/ZBAA). The flight was a regularly scheduled passenger flight destined to San Francisco International Airport, San Francisco, California, (SFO). The flight was climbing through 23,000 feet in the vicinity of Tangshan, China at the time of the encounter. The encounter resulted in serious injury to one flight attendant and minor injuries to four flight attendants. There were no injuries to the four flight crew members, 10 other flight attendants and 366 passengers which included one lap child. The airplane was not damaged. The Civil Aviation Authority of China delegated the investigation of the accident to the U.S. NTSB. The crew reported that after numerous ground delays due to passenger and ATC issues, the takeoff and climbout was normal. A small amount of clouds and rain were in the area, but the Captain reported there were no weather radar returns along the intended path. The Captain reported she used ranges from 5 to 80 miles and different antenna tilts, and noted she used the Doppler radar functions which can depict turbulence. The Captain kept the seatbelt sign illuminated, but advised the cabin crew that they could begin service at their own discretion. According to the flight crew, while climbing through about 22,000 to 24,000 feet the airplane encountered “severe turbulence” and described violent pitch, altitude and airspeed excursions. The flight attendants had begun cabin service and were working with beverage carts and other galley work, when they described a “violent” or “severe” jolt to the airplane. The Captain disengaged the autopilot and attempted to maintain climb pitch attitude. She retarded the throttle to avoid an overspeed. Recorded flight data indicated a peak vertical acceleration of over 2 G’s, and acceleration fluctuations continued for about 20 seconds. After the turbulence subsided, the Captain reengaged the autopilot and advised ATC. The purser advised the Captain that the flight attendant at door 5L was injured, with a possible broken fibula. A passenger medical doctor on board had examined the flight attendant and advised that he thought she had a severely sprained ankle, and possibly a fibula fracture, but that he did not see a need to immediately divert. The flight attendant was insistent that she wished to continue the flight to the U.S. to receive medical attention. The Captain, attending physician and injured flight attendant determined the injuries did not require immediate attention. The Captain relayed the information to dispatch, having already advised them of the severe turbulence encounter. The purser made arrangements to move the injured flight attendant to a business class seat, and applied a make-shift splint to her leg. They elevated her leg with pillows and applied ice to her ankle. The Captain arranged to have paramedics meet the airplane upon arrival at SFO. INJURIES TO PERSONS One flight attendant received a fracture to her right fibula. There were minor injuries reported to four additional flight attendants, from falls and impacts with galley service equipment, however they were able to continue cabin crew duties and safety responsibilities. There were no injuries to the four flight deck crewmembers, 10 other cabin crewmembers, and 366 passengers which included one lap child. DAMAGE TO AIRCRAFT United Airlines maintenance performed a post-flight severe turbulence inspection, and reported no damage findings. OTHER DAMAGE None PERSONNEL INFORMATION The captain, age 59, had worked for United Airlines since January 09, 1978. She held an FAA Airline Transport Pilot certificate, multi-engine land, with type ratings in B737, B747-400 and NA265. She held an FAA first class medical certificate with a limitation to wear corrective lenses. She had about 18,500 hours total time with about 7,600 hours as pilot-in-command on the B747. The first officer, age 62, had worked for United Airlines since March 9, 1987. He held an Airline Transport Pilot certificate, multi-engine land, with type ratings in B747-400, B737, and B767. He held an FAA first class medical certificate with no limitations or waivers. He reported a total of 10,212 flight hours total time, with 8,557 hours in the B747. Two relief pilots were also seated in the cockpit at the time of the event. AIRCRAFT INFORMATION N173UA, manufacturer serial number 24380, was a Boeing 747-422 equipped with four Pratt & Whitney 4056 engines. The airplane had approximately 83,255 hours total time on the airframe. Recorded data and airline records indicated no relevant maintenance issues with the airplane. METEOROLOGICAL INFORMATION An NTSB Meteorologist compiled information from the China CAAC and other sources to conduct a study of the conditions forecast and occurring in the vicinity of the accident. Additionally, United Airlines contract weather service (ENSCO) compiled a weather study. A cold front was producing a large area of clouds and weather along a line from eastern Mongolia, central and eastern Inner-Mongolia, into Shanxi Province. Several areas of embedded convective cloud groups were identified along and ahead of the front, with Beijing and the area to the east of Beijing covered by convective cloud groups. The sea port of the Bohai Sea, located 160 km or 86 miles east of Beijing was also covered by strong thunderstorms. The Beijing upper air sounding depicted a moist low level environment with the relative humidity greater than 75 percent from the surface through 5,000 feet and between 15,000 and 32,000 feet, generally associated with an unstable air mass. Satellite visible and infrared imagery indicated a large area of embedded convective activity around the accident location with the most activity southwest of the location moving to the northeast. A SIGMET (significant meteorological warning) warned of embedded thunderstorms obscured and forecast with tops to 33,000 feet, south and southwest and northeast of Beijing, moving northeast at 30 kilometers per hour (18 knots). The preflight dispatch indicated that there was a chance of embedded thunderstorms departing the Peking FIR and that the dispatcher had increased the flight’s taxi fuel for possible weather related departure delays. The dispatcher further indicated that there was enroute turbulence forecasted for the route. The National Weather Service High Level Significant Weather Prognostic Chart issued for the accident time period did not predict convection over the Beijing area or the accident site, however it did include a line of isolated embedded thunderstorms with tops to 46,000 feet extending immediately east of Beijing to the Bohai Sea southwest through China along the planned route of flight. AIDS TO NAVIGATION Not applicable COMMUNICATIONS The CAAC found no recorded radio transmissions with Air Traffic Control regarding the turbulence or injury. AERODROME INFORMATION Not applicable FLIGHT RECORDERS The Quick Access Recorder (QAR) was downloaded by United Airlines with the approval of the NTSB recorders laboratory. QAR data was used to create plots and a flight path map and information is incorporated in the History of Flight section of the report. The Digital Flight Data Recorder was quarantined, but not used for this event. The Cockpit Voice Recorder was overwritten during the flight to SFO and did not contain accident data. WRECKAGE AND IMPACT INFORMATION Not applicable MEDICAL AND PATHOLOGICAL INFORMATION Not applicable FIRE None SURVIVAL ASPECTS The seat belt sign was illuminated, however cabin crew were advised by the Captain that they could begin cabin service. The flight attendants reported that they had just begun cabin service when the turbulence encounter occurred. United Airlines procedures allow flight attendants to be out of their seats and up when the seatbelt sign is on unless pilots instruct the flight attendants to remain seated. TESTS AND RESEARCH Not applicable ORGANIZATIONAL AND MANAGEMENT INFORMATION Not applicable ADDITIONAL INFORMATION Not applicable
an inadvertent encounter with convectively induced turbulence likely due to radar limitations and convective weather developing upwards into the flight path.
Source: NTSB Aviation Accident Database
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