American Airlines Flight 288

A flight attendant was seriously injured during an in-flight encounter with unforecast moderate to severe turbulence. The international air carrier flight was in cruise flight at the time of the accident. The captain stated the flight "encountered a brief (2-3 second) but very intense moderate-to-severe turbulence event" at flight level 340. He noted that continuous moderate turbulence continued for approximately 30 seconds, and periods of occasional-to-continuous moderate chop continued for about 10 minutes after the initial encounter. He added that there were no returns on the weather radar, and no pilot reports or adverse ride reports received from air traffic control. The fasten seat belt sign was on at the time of the encounter because the flight had encountered light chop after leveling off at cruise altitude. He reported that the ride had been smooth for approximately 10 minutes prior to the turbulence event. The injured flight attendant stated that she was working in the aft galley when the turbulence began. She reported that she hit her head on the ceiling and landed on the galley floor with her leg bent under her. The Flight Data Recorder (FDR) revealed that the airplane encountered a vertical acceleration ranging from 0.245 G to 1.246 G. The data also indicated that the autopilot was engaged, and no pitch inputs were made from the cockpit at the time of the encounter. Postaccident inspections did not reveal any damage to the airplane.

Verbatim NTSB analysis and probable cause from the NTSB dataset