What happened
During an initial descent into St. Louis, a Boeing 727 operated by TWA, identified as Flight 374, encountered severe clear air turbulence while passing over Cape Girardeau at FL220. The aircraft had recently been cleared to a lower altitude after the crew began experiencing bumpy conditions.
The turbulence resulted in two injuries among the cabin crew: one flight attendant sustained a broken clavicle, and another flight attendant suffered bruised ribs.
Prior to the encounter, shortly after the flight departed from New Orleans, LA, a SIGMET had been issued for moderate occasional severe turbulence between FL240 and FL350.
The investigation
Analysis of the flight data recorder revealed significant vertical acceleration fluctuations during the event. The recorded data showed changes in vertical acceleration ranging from +2.5g's to -0.79g's.