Incident Overview
During vectoring between two thunderstorm cells in instrument meteorological conditions (IMC), the airplane momentarily entered visual meteorological conditions (VMC). The flightcrew observed a cumulonimbus buildup directly ahead of their path. The captain reported that this buildup had not been displayed on their radar and that the cell was too close to avoid.
Crew Actions
The captain immediately made an announcement for the flight attendants, who were in the process of serving the cabin, to be seated. However, the captain stated that there was not enough time for the flight attendants to react before the airplane penetrated the top of the buildup.
Turbulence and Altitude Loss
The flight experienced ten seconds of severe turbulence. During this event, the airplane lost approximately 900 feet in altitude.
Injuries
Three of the nine flight attendants were seriously injured. One passenger, who was seated but had not had her seat belt fastened, was also seriously injured.
Seat Belt Sign Status
The seat belt sign had been on for approximately eight to ten minutes prior to the cell penetration.