Incident Overview
A flight operating between Minneapolis and Chicago experienced unexpected turbulence while descending at 19,680 feet mean sea level (msl). The turbulence resulted in minor injuries to four passengers and four flight attendants, with one passenger sustaining a broken ankle.
Flight History
The flight had originally diverted to Minneapolis due to thunderstorm activity in the Chicago area. Following the diversion, the flight departed Minneapolis en route to Chicago. According to the captain, the flight was smooth until the abrupt turbulence was encountered. At the time of the encounter, the seat belt sign was not illuminated.
Weather and Flight Planning
Prior to departing Minneapolis, the flight crew received a Weather Briefing Message (WBM) that contained convective SIGMETs for Wisconsin, Illinois, and Indiana. The turbulence occurred ahead of a stationary front that extended northeast-southwest through central Wisconsin and Iowa. This front had been generating showers and thunderstorm activity throughout the afternoon and evening on the day of the incident.
Recorded Data
Analysis of data from the Quick Access Recorder (QAR) indicated that the aircraft experienced a change in vertical G-loading from 0.0843 g to 1.9375 g over a two-second period while at an altitude of 19,680 feet msl.