# NTSB WPR11LA203: Boeing 777-223, N766AN, Pacific Ocean, April 11, 2011 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Limited investigation · Final report - Date: April 11, 2011, 07:00 UTC - Place: Pacific Ocean - Coordinates: 35.893333, 143.871673 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=35.8933&lon=143.8717&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-climb to cruise: Turbulence encounter](https://openairdocs.org/ntsb-events/360) - Highest injury: Serious injuries - Injuries: 2 serious, 2 minor, 227 uninjured - Status: Completed, report November 29, 2011 - Report: Approved by Office Director - NTSB office: Western Pacific Region - NTSB case key (mKey): 78892 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR11LA203 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/78892/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=78892 - Page: https://openairdocs.org/ntsb/WPR11LA203 ## Probable cause An inadvertent encounter with convective-induced turbulence upon entering cumulonimbus clouds. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Turbulence: convective turbulence](https://openairdocs.org/ntsb-findings/03032020): Environmental issues › Conditions/weather/phenomena · Effect on personnel (probable cause); cases with it: [Boeing 777-223, 4 cases](https://openairdocs.org/ntsb-findings/03032020/cases.md?model=1385213), [All aircraft, 145 cases](https://openairdocs.org/ntsb-findings/03032020/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-climb to cruise: Turbulence encounter](https://openairdocs.org/ntsb-events/360) (defining event); cases with it: [Boeing 777-223, 10 cases](https://openairdocs.org/ntsb-events/360/sequence.md?model=1385213), [All aircraft, 423 cases](https://openairdocs.org/ntsb-events/360/sequence.md) ## Analysis As the airplane was climbing, the flight crew observed a small weather buildup in front of them. They requested a deviation around the weather, but the air traffic controller requested that they stand by. After entering the weather, they received clearance to turn; however, about 24,000 feet, the airplane encountered about 11 seconds of moderate, and then severe, turbulence. During the encounter, two flight attendants received broken ankles while conducting work in the aft cabin area. The digital flight data recorder revealed that during the encounter vertical acceleration forces went from 2.2G to 0.6913G within 1 second, to a minimum of 0.496G about 5 seconds after the 2.2G maximum. A weather study conducted by a National Transportation Safety Board meteorologist revealed a frontal wave over the Japanese coast with a warm front extending eastward in the vicinity of the turbulence encounter. A gale force wind was expected. The region of the turbulence encounter also contained low to mid-level clouds with cloud tops near 14,000 feet; cumulonimbus cloud development, with tops up to 26,000 feet, was slightly upstream from the turbulence encounter. Review of the weather package given to the flight crew found no forecasts for turbulence and no Significant Meteorological Information advisories (SIGMETS) were in effect for the route of flight. At the time of the occurrence, there were no reports of turbulence from pilots ahead of the accident flight and the flight crew saw no indication of turbulence on their weather radar. ## Factual narrative On April 11, 2011, at 6:58:38 coordinated universal time (UTC), American Airlines Flight 170, a Boeing 777-223, N766AN, experienced severe turbulence during climb over international waters about 194 nautical miles east of Narita, Japan. Four flight attendants were injured; two flight attendants sustained minor injuries, while two flight attendants sustained serious injuries. There were no injuries to the other 227 passengers and crew, and the airplane was not damaged. The scheduled international passenger flight originated from Narita International Airport, Narita Japan and was en route to Los Angeles International Airport, Los Angeles, California under the provisions of Title 14 Code of Federal Regulations Part 121. The flight crew reported that as the airplane was climbing, they observed a small weather build up in front of them. They requested a deviation around the weather, but ATC informed them to standby. The first officer reported that when the flight crew received the clearance to turn the airplane was already in the weather. At about 24,000 feet, the airplane encountered moderate then severe turbulence for about 11 seconds. Although the seatbelt signs were still illuminated from takeoff, the flight attendants were working in the cabin at the time of the occurrence. During the turbulence encounter, both the number 2 and number 3 flight attendants received fractured ankles. The number 2 flight attendant was working in the aft galley when she was thrown to the floor of the airplane, landing hard on her right hand and the outside of her right ankle. The number 3 flight attendant was washing her hands in the 4R lavatory when she could not maintain balance and fell, striking her right foot. The Digital Flight Data Recorder (DFDR) was sent to the National Transportation Safety Board (NTSB) recorders division for data analysis. According to the DFDR data, the event occurred at 6:58:38; at this time, the airplane was at a pressure altitude of about 24,000 feet, with a speed of 336 KIAS. During the event, the vertical acceleration went from 2.2G’s to 0.6913G’s within 1 second, to a minimum G of 0.496 about 5 seconds after the 2.2G maximum. A weather study conducted by a NTSB meteorologist revealed a frontal wave over the Japanese coast with a warm front extending eastward in the vicinity of the turbulence encountered; developing gale force winds were expected. An upper level chart for 18,000 feet depicted west-southwesterly winds of 40-45 knots in the region. The region also contained low to mid-level clouds with cloud tops near 14,000 feet; cumulonimbus cloud development, with tops up to 26,000 feet, was slightly upstream from the turbulence encounter. At 0732, an airplane along a similar route reported wind at 24,000 feet from 245 degrees at 65 knots. Review of the weather package given to the flight crew by American Airlines dispatch found no forecasts for turbulence. No SIGMETS were in effect for the route of flight. At the time of theoccurrence, there were no reports of turbulence from airplanes ahead of the accident flight, and the flight crew saw no indications on their weather radar of any returns. ## Aircraft - Registration: [N766AN](https://openairdocs.org/aircraft/N766AN), registered now, S/N 32880, built 2003 (OpenAirDocs) - Reported make and model: BOEING 777-223 - Registry model: [Boeing 777-223](https://openairdocs.org/model/boeing-777-223) (registry code 1385213) (OpenAirDocs) - Registry engine: [Rolls-Royce RB-211 series](https://openairdocs.org/engine/rolls-royce-rb-211-series) (registry code 54555, turbo-fan) (OpenAirDocs) - Category: Airplane - Serial number: 32880 - Airframe hours: 33558 - Engines: Rolls Royce Trent 892 turbo fan - Damage: No damage - Flight: Part 121 - Operator: American Airlines Inc - Registered owner: American Airlines Inc - Airworthiness certificate: Standard, Transport - Departed: NRT, Narita - Destination: LAX, Los Angeles, CA - Flight plan: IFR - Airport: NRT, Narita International Airport ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 61; injuries: none; flight engineer, airline transport; airplane ratings: multi-engine land; instrument ratings: airplane; medical: class 1, with waivers/limitations; last flight review October 26, 2010; seat: left; flight hours: 174 in the last 90 days, 82 in the last 30 days, 0 in the last 24 hours - Co-pilot; age 54; injuries: none; flight engineer, airline transport; airplane ratings: multi-engine land; instrument ratings: airplane; medical: class 1, without waivers/limitations; last flight review February 15, 2011; flight hours: 47 in the last 90 days, 47 in the last 30 days, 0 in the last 24 hours - Co-pilot; age 56; injuries: none; flight engineer, airline transport; airplane ratings: multi-engine land; instrument ratings: airplane; medical: class 1, with waivers/limitations ## Weather - Conditions: Visual (VMC), Day - Wind: 245° at 65 knots - Visibility: 25 statute miles - Temperature: -36 °F - Observed at: NRT, 194 nm away ## Other investigations on N766AN (1) From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [NTSB OPS11IA246](https://openairdocs.org/ntsb/OPS11IA246), Jan 21, 2011: Boeing 777 (N766AN), 80 SE of JFK (Atlantic Ocean), NY, incident, no damage. Probable cause: Incomplete and incorrect coordination between air traffic controllers that resulted in the 777 and the two C17s being cleared to maintain the same altitude. Contributing to the incident was the… ## Docket (6 files) The files NTSB released with the investigation on October 21, 2011, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=78892. 29.7 MB in all. - Flight Data Recorder 10 - Factual Report of FDR Specialist (item 1, .PDF, 342 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40347785&FileExtension=.PDF&FileName=Flight%20Data%20Recorder%2010%20-%20Factual%20Report%20of%20FDR%20Specialist-Master.PDF - Flight Data Recorder 10 - Attachment 1 - Comma Separated Data (CSV) File (item 2, .CSV, 27.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40347788&FileExtension=.csv&FileName=Flight%20Data%20Recorder%2010%20-%20Attachment%201%20-%20Comma%20Separated%20Data%20(CSV)%20File-Master.csv - Meteorology 5 - Weather Study (item 3, .PDF, 11 photos, 803 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40349895&FileExtension=.PDF&FileName=Meteorology%205%20-%20Weather%20Study-Master.PDF - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 4, .PDF, 620 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40346962&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Flight Crew and Flight Attendant Statement - from American Airlines (item 5, .PDF, 65 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40349102&FileExtension=.PDF&FileName=Flight%20Crew%20and%20Flight%20Attendant%20Statement%20-%20from%20American%20Airlines-Redacted.PDF - Weather Reports - Flight Crew Weather Package (item 6, .PDF, 66 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40346963&FileExtension=.PDF&FileName=Weather%20Reports%20-%20Flight%20Crew%20Weather%20Package-Master.PDF From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.