Event Details


Title:Turbulence injuries, Boeing 737-242C, March 4, 1998
Micro summary:This Boeing 737-242C experienced turbulence in cruise, injuring several people.
Event Time:1998-03-04 at 1315 PST
File Name:1998-03-04-US.pdf
Publishing Agency:National Transportation Safety Board (NTSB)
Publishing Country:USA
Report number:LAX98LA104
Pages:5
Diversion Airport:Reno/Tahoe International Airport, Reno, Nevada, USA
Site of event:Reno, NV
Departure:Seattle-Tacoma International Airport, Seattle, Washington, USA
Destination:McCarran International Airport, Las Vegas, Nevada, USA
Airplane Type(s):Boeing 737-242C
Flight Phase:Cruise
Registration(s):N746AS
Operator(s):Alaska Airlines
Type of flight:Revenue
Occupants:116
Fatalities:0
Serious Injuries:1
Minor/Non-Injured:115
Other Injuries:0
Diverted to:Reno/Tahoe International Airport, Reno, Nevada, USA
Executive Summary:

NTSB short summary:

Unforecasted and sudden encounter with clear air turbulence when passengers and flight attendants were not secured in their seats.

NTSB synopsis:

The fight encountered severe clear air turbulence en route at flight level 350 and diverted to Reno, Nevada.. There were no reports of clear air turbulence from other pilots nor was it forecasted. The seat belt signs were off at the time. A review of the flight data recorder indicated that, for the period involved, vertical acceleration (Nz) varied from +1g to +1.5g to -0.07g to +1.3g to +0.86g over a 6-second period. The recorded data also indicated that atmospheric stability existed at flight level 350 several minutes prior to the turbulent onset. There was little or no warning given to the flight crew of the impending turbulent conditions.

NTSB factual narrative text:

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.
Learning Keywords:Operations - Turbulence
Consequence - Flight Attendant Fatality - Injury
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