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ASN Wikibase Occurrence # 121809
Last updated: 18 January 2022
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Type:Silhouette image of generic B772 model; specific model in this crash may look slightly different
Boeing 777-223ER
Owner/operator:American Airlines Inc
Registration: N766AN
MSN: 32880/445
Fatalities:Fatalities: 0 / Occupants: 231
Aircraft damage: None
Location:~194 nm east of RJAA -   Pacific Ocean
Phase: Initial climb
Nature:Passenger - Scheduled
Departure airport:Narita, (NRT)
Destination airport:Los Angeles, CA (LAX)
Investigating agency: NTSB
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.
Probable Cause: An inadvertent encounter with convective-induced turbulence upon entering cumulonimbus clouds.




Photo of N766AN courtesy

Los Angeles - International (KLAX / LAX)
29 November 2016; (c) Danny Grew

Revision history:

20-Apr-2011 12:05 espeluk Added
21-Apr-2011 02:22 harro Updated [Date, Time, Total occupants, Source]
21-Dec-2016 19:25 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
27-Nov-2017 16:51 ASN Update Bot Updated [Cn, Operator, Other fatalities, Departure airport, Destination airport, Source, Narrative]

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