Incident Overview
On August 11, 2016, at approximately 2010 central daylight time, JetBlue Airways Flight 429, an Airbus A-320-232 registered as N632JB, experienced severe turbulence during cruise flight. The aircraft diverted to Rapid City Regional Airport (KRAP) in Rapid City, South Dakota. The flight was a regularly scheduled domestic passenger operation under 14 CFR Part 121, originating from Boston Logan International Airport (KBOS) and destined for Sacramento International Airport (KSMF). Onboard were 151 passengers and crew, of whom 31 sustained minor injuries.
Flight and Turbulence Encounter
The flight departed on schedule, with uneventful taxi, takeoff, and initial climb. The captain was the pilot flying and the first officer was the pilot monitoring at the time of the event. The flight had been experiencing intermittent light chop turbulence, and the crew queried air traffic control (ATC) about a higher altitude for smoother conditions. The controller advised that turbulence would be worse at a higher altitude, so the crew decided to remain at flight level 320. Shortly before the turbulence encounter, the onboard weather radar depicted precipitation ahead, and ATC advised of moderate precipitation. The captain subsequently informed the flight attendants to be seated in their jumpseats and turned on the seatbelt sign.
After the flight exited some light precipitation, the crew observed cumulonimbus clouds and requested a deviation to the left, which was cleared. As the airplane flew through the edge of the clouds, it encountered turbulence described by the captain as "very violent and very quick." During the encounter, computed airspeed increased from about 275 knots to 285 knots while the airplane was in a left bank. Vertical acceleration increased to +1.7 g, then fluctuated at positive g values for about 6 seconds before decreasing to a maximum negative value of 0.75 g.
Cabin Events and Injuries
Flight attendants reported that the flight had been experiencing light turbulence when the captain called them to state that conditions would be similar for the next 30 to 45 minutes. One flight attendant made an announcement for passengers to remain seated with seatbelts fastened. At that time, all three flight attendants were seated in their jumpseats. The turbulence continued for about 10 minutes before smoothing out, after which the flight attendants got up to conduct various tasks throughout the cabin. The airplane subsequently encountered what they described as "extreme" and "violent" turbulence, causing all three flight attendants to sustain injuries.
Diversion and Aftermath
Following the turbulence encounter, the captain contacted the flight attendants via the interphone and was informed of their injuries. He decided to divert to Rapid City Regional Airport and transferred control to the first officer so that he could go back to the cabin to assess the injuries.
Meteorological Conditions
A review of the flight plan showed that convective SIGMETs and thunderstorms were forecasted and valid on or near the route of flight. However, the pilots reported that they only saw areas of green returns on their onboard radar and did not see any indication of severe weather. Additionally, there were no pilot reports (PIREPs) indicating that other aircraft were encountering severe turbulence, nor any advisories of turbulence from air traffic control.