NTSB Identification: DCA02MA029.
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Scheduled 14 CFR operation of Northwest Airlines
Accident occurred Friday, March 22, 2002 in int'l waters
Probable Cause Approval Date: 05/18/2004
Aircraft: McDonnell Douglas DC-10-30, registration: N234NW
Injuries: 1 Serious,4 Minor,257 Uninjured.
NTSB investigators traveled in support of this investigation and used data obtained from various sources to prepare this aircraft accident report.
A flight attendant was seriously injured when the airplane encountered turbulence while descending from flight level (FL) 350 to FL 340. Flight crew interview statements indicated that they were preparing for turbulence and that they wanted the passengers and flight attendants seated with their seatbelts fastened. However, the flight crew did not advise the lead flight attendant (LFA) of the turbulence level and its anticipated duration nor did they use turbulence codes, as stipulated in Northwest Airlines' Flight Operations Manual. The investigation also revealed that the LFA did not relay the turbulence information to all of the flight attendants, as stipulated in the company's Flight Attendant Manual.
Examination of the restraint system from the injured flight attendant's jump seat indicated that the restraint system did not fail during the turbulence upset. The Safety Board was unable to determine whether the lapbelt was improperly secured by the flight attendant or whether it was inadvertently disengaged during the turbulence upset.
The Safety Board's investigation examined the turbulence and the flight crew's operation of the airplane during the turbulence encounter to evaluate the effects on the airplane occupants. Analysis of the flight data recorder (FDR) data indicates that the turbulence caused substantial vertical and lateral oscillations, which may have made it difficult for the first officer (as the flying pilot) to maintain a constant pitch attitude.
The FDR data showed variations in the airplane's pitch attitude during the turbulence encounter. Despite the airplane's pitch excursions, statements from the flight crew indicate that they were attempting to maintain constant pitch attitudes during the turbulence upset. Nevertheless, FDR data indicate that the large and rapid pitch excursions were primarily a result of control column inputs made by the first officer. The Safety Board's investigation determined that the main pitchover (which likely caused the flight attendant's injuries) occurred as a result of the first officer's control inputs.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The flight attendant's injuries were a result of her unsecured lap belt and shoulder harness for undetermined reasons, and the oscillations of the airplane, which were caused by turbulence and large control column inputs by the first officer. Contributing to the flight attendant's injuries was the failure of the flight crew and the lead flight attendant to follow company procedures regarding dissemination of turbulence information. Full narrative available
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