Summary
On March 04, 1998, a Boeing 737-242C (N746AS) was involved in an accident near Reno, NV. The accident resulted in 1 serious injury, 5 minor injuries, with 110 people uninjured out of 116 aboard.
The National Transportation Safety Board determined the probable cause of this accident to be: Unforecasted and sudden encounter with clear air turbulence when passengers and flight attendants were not secured in their seats.
On March 4, 1998, at 1315 hours Pacific standard time, Alaska Airlines Flight 684, a Boeing 737-242C, N746AS, encountered severe clear air turbulence (CAT) at flight level (FL) 350 approximately 90 miles north-northeast of Reno, Nevada. There was no damage to the aircraft. Of the 116 personnel onboard, 3 passengers and 2 flight attendants received minor injuries, and 1 flight attendant suffered a broken ankle. Due to the injuries, the flight diverted to Reno. Visual meteorological conditions prevailed at the time. The flight was operated by Alaska Airlines, Inc., as a non-stop, regularly scheduled domestic passenger flight from Seattle to Las Vegas.
According to the operator, en route conditions were smooth up until the event.
This accident is documented in NTSB report LAX98LA104. AviatorDB cross-references NTSB investigation data with FAA registry records to provide comprehensive safety information for aircraft N746AS.
Accident Details
Probable Cause and Findings
Unforecasted and sudden encounter with clear air turbulence when passengers and flight attendants were not secured in their seats.
Aircraft Information
Analysis
On March 4, 1998, at 1315 hours Pacific standard time, Alaska Airlines Flight 684, a Boeing 737-242C, N746AS, encountered severe clear air turbulence (CAT) at flight level (FL) 350 approximately 90 miles north-northeast of Reno, Nevada. There was no damage to the aircraft. Of the 116 personnel onboard, 3 passengers and 2 flight attendants received minor injuries, and 1 flight attendant suffered a broken ankle. Due to the injuries, the flight diverted to Reno. Visual meteorological conditions prevailed at the time. The flight was operated by Alaska Airlines, Inc., as a non-stop, regularly scheduled domestic passenger flight from Seattle to Las Vegas.
According to the operator, en route conditions were smooth up until the event. The Captain noted no turbulence, chop, etc., and there were no reports by other aircraft of any turbulence. After level off, the seat belt signs were turned off and the normal announcement made by the flight crew to keep the seat belts fastened while seated. Normal service was in progress in the cabin at the time of the accident.
A review of the flight recorder data indicated that, for the CAT period involved, vertical acceleration (Nz) varied from +1.0g to +1.51g to -0.07g to +1.3g to +0.86g over a 6-second interval. (See enclosed sketch and FDR time histories.) The recorded data also indicated stable atmospheric conditions (Nz = 1.0g) at FL 350 during the several minutes prior to CAT onset.
Data Source
Data provided by the National Transportation Safety Board (NTSB). For more information on this event, visit the NTSB Records Search website. NTSB# LAX98LA104