A SIGMET Advisory Was Issued At 1213 Which Forecasted Occasional Severe Turbulence Between FL270 and FL400

Location: Henderson, NV Accident Number: DCA25FA071
Date & Time: December 26, 2024, 13:35 Local Registration: N958AK
Aircraft: Boeing 737 Injuries: 2 Serious, 1 Minor, 181 None
Flight Conducted Under: Part 121: Air carrier - Scheduled

On December 26, 2024, at 1335 pacific standard time, Alaska Airlines flight 700, a Boeing 737 9, N958AK, encountered severe turbulence during cruise flight, near Henderson, Nevada. Of the 181 passengers and crew, two flight attendants received serious injuries, and one received a minor injury. The flight was conducted under the provisions of Title 14 Code of Federal 
Regulations Part 121 scheduled domestic passenger flight from Seattle-Tacoma International Airport (SEA), Seattle, Washington, to Phoenix Sky Harbor International Airport (PHX), Phoenix, Arizona. 

The flight crew reported that during the first half of the flight, the turbulence they experienced was “no worse than light chop”. They were aware that worse turbulence was expected during the second half of the flight, as indicated by weather products and advisories provided in the dispatch paperwork for the flight. Additionally, they monitored a company weather app and had communication with their dispatch while enroute for any updates to weather conditions and turbulence forecasts. 

Before the flight, the pilots had briefed the lead flight attendant in advance about when they should perform service and prepare for landing, due to the expected turbulence. As the airplane approached the area of expected turbulence, while at flight level (FL) 330, the first officer made a public address announcement to advise the passengers that the seatbelt sign 
would be turned on in about 15 minutes, and the flight attendants would then also be seated. The airplane encountered light turbulence 15 minutes later, and the first officer turned on the seatbelt sign and informed the flight attendants that the turbulence was expected to worsen, and that they should prepare the cabin and take their seats. The first officer checked in with air traffic control (ATC) and reported experiencing light with occasional moderate turbulence. ATC advised that there were areas of light chop throughout the Las Vegas area, and that there were no reports of turbulence more intense than the light chop. 

About 15 minutes later the airplane encountered severe turbulence. Two flight attendants were seriously injured, and one non-revenue flight attendant passenger sustained a minor injury. All were located in the rear gally area when the turbulence occurred and were not restrained. The pilots declared a medical emergency and elected to continue to Phoenix, after determining that a diversion to the nearest airport would result in routing through the area of expected turbulence. The remainder of the flight was uneventful. EMS personnel met the airplane at the gate and four flight attendants were subsequently transported to the hospital. 

A post accident review of weather data revealed that a Significant Meteorological Information (SIGMET) advisory was issued at 1213 which forecasted occasional severe turbulence between FL270 and FL400 due to wind shear associated with the jetstream in an area surrounding the accident location. A pilot report (PIREP) had previously included such conditions 5 minutes prior to the accident in the general vicinity of the turbulence encounter location. Additionally, an Airman’s Meteorological Information (AIRMET) advisory was issued for the area at 1245, which forecasted moderate turbulence between FL180 and FL400. 
Satellite and weather radar data for the accident area indicated there was cloud cover above the turbulence encounter locations and no precipitation echoes, respectively. 

Qualified parties were invited to participate in the investigation. These included Alaska Airlines, the Federal Aviation Administration (FAA) and National Air Traffic Controllers Association. The following NTSB specialists were assigned to investigate the accident: Air Traffic Control, Meteorology, and Operations. The investigation is continuing. 

FMI: www.ntsb.gov