Incident Overview

Date: Wednesday 4 March 1998
Aircraft Type: Boeing 737-242C
Owner/operator: Alaska Airlines
Registration Number: N746AS
Location: Reno, NV – ÿ United States of America
Phase of Flight: En route
Casualties: Fatalities: 0 / Occupants: 116
Component Affected: Flight data recorderFlight data recorder
Investigating Agency: NTSBNTSB
Category: Accident
Narrative
A flight experienced severe clear air turbulence at flight level 350, resulting in a diversion to Reno, Nevada. The flight crew failed to adequately prepare for the turbulence, and the lack of seat belt signs contributed to the incident. Vertical acceleration data revealed significant fluctuations during the turbulent period, suggesting a sudden and unexpected event. The incident was likely caused by unforeseen clear air turbulence.A flight experienced severe clear air turbulence at flight level 350, resulting in a diversion to Reno, Nevada. The flight crew failed to adequately prepare for the turbulence, and the lack of seat belt signs contributed to the incident. Vertical acceleration data revealed significant fluctuations during the turbulent period, suggesting a sudden and unexpected event. The incident was likely caused by unforeseen clear air turbulence.

Description

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

Primary Cause

Unforecasted and sudden encounter with clear air turbulence.Unforecasted and sudden encounter with clear air turbulence.

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