What happened
While descending from flight level 350 to flight level 340, the aircraft encountered turbulence. During this period, a flight attendant sustained serious injuries. The flight crew had been preparing for turbulence and intended to ensure all passengers and flight attendants were seated with seatbelts fastened. However, the crew did not notify the lead flight attendant of the expected intensity or duration of the turbulence, nor did they utilize the required turbulence codes specified in the Northwest Airlines Flight Operations Manual.
Furthermore, the lead flight attendant failed to relay necessary turbulence information to the rest of the flight attendant crew, as required by the company's Flight Attendant Manual.
The investigation
Investigators examined the restraint system on the injured flight attendant's jump seat and found that the system did not fail during the event. It could not be determined if the lapbelt was improperly secured or if it became disengaged during the turbulence.
Analysis of the flight data recorder (FDR) revealed that the turbulence caused substantial vertical and lateral oscillations. While the flight crew stated they were attempting to maintain a constant pitch attitude, the FDR data showed significant variations in pitch. The investigation determined that these large and rapid pitch excursions were primarily driven by control column inputs made by the first officer, who was acting as the flying pilot.
Findings
- The primary pitchover event that likely caused the injuries resulted from control column inputs by the first officer.
- The flight crew failed to follow company procedures regarding turbulence notification and coding.
- The lead flight attendant did not communicate turbulence information to all cabin crew members.