NTSB Identification: DCA98MA015.
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Scheduled 14 CFR UNITED AIRLINES, INC.
Accident occurred Sunday, December 28, 1997 in PACIFIC OCEAN
Probable Cause Approval Date: 05/14/2001
Aircraft: Boeing 747-122, registration: N4723U
Injuries: 1 Fatal,18 Serious,171 Minor,203 Uninjured.
NTSB investigators traveled in support of this investigation and used data obtained from various sources to prepare this aircraft accident report.
The flightcrew inadvertently flew into an area of clear air turbulence. Weather forecasts indicated that there was not to be turbulence in the area where it was encountered. The ability to forecast clear air turbulence over the ocean is limited. In addition, the Japanese-speaking flight attendant did not fully translate one of the captain's instructions to fasten seat belts into Japanese, although such an announcement was made and translated several times prior to the turbulence encounter. Most of the passengers spoke only Japanese.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The pilot-in-command's inadvertent flight into adverse weather conditions, and the difficulty of obtaining adequate weather forecasts of over-ocean turbulence. Factors contributing to the accident include the presence of clear air turbulence, and the failure of the flight attendant to issue a safety advisory. Full narrative available
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