NTSB Identification: SEA08LA050
Scheduled 14 CFR Part 121: Air Carrier operation of Alaska Airlines, Inc.
Accident occurred Tuesday, December 25, 2007 in Ontario, CA
Probable Cause Approval Date: 01/14/2009
Aircraft: MCDONNELL DOUGLAS DC-9-83, registration: N943AS
Injuries: 2 Serious,112 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
Two flight attendants were seriously injured when the airplane encountered severe turbulence while descending for landing. The turbulence was likely the result of strong easterly winds interacting with the rough terrain in the area (mechanical turbulence). The flight data recorder data indicates that the airplane experienced a vertical acceleration of +0.4 G to +1.9 G, or 1.5 G total change, which corresponds to severe turbulence. The National Weather Service forecast the severe turbulence in Significant Meteorological Advisory (SIGMET) Victor 2, which was issued before the flight departed. The weather company that provides weather information to the operator did not forecast severe turbulence for the area. The content of SIGMET Victor 2 was available to the flight's dispatcher. However, this information was not provided to the flight crew. The two flight attendants who sustained injuries were both standing, completing final cabin duties in preparation for landing, and were knocked to the floor during the turbulence encounter.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The lack of turbulence forecasts available to the flight crew, which resulted in the flight attendants not being seated when the flight encountered severe terrain-induced turbulence. Contributing to the accident were the terrain-induced turbulence, the failure of the company that provided the flight's weather briefing to forecast severe turbulence, and the failure of the dispatcher to provide the National Weather Service severe turbulence forecast to the flight. Full narrative available
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