What happened
On February 20, 2009, a Northwest Airlines Boeing 747-40 and registered N676NW, flying from Manila to Narita, encountered severe atmospheric disturbances. While descending through approximately 30,300 feet about 174 km south-southwest of Narita International Airport, the aircraft entered a region of intense turbulence near convective clouds and the jet stream.
During the encounter, the aircraft experienced significant vertical acceleration fluctuations, ranging from +1.70G to -0.52G, accompanied by sudden changes in wind velocity. The turbulence caused the aircraft to pitch sharply, leading to internal damage, including detached cabin panels. The incident resulted in four passengers sustaining serious injuries and 34 others, including flight attendants, sustaining minor injuries.
The investigation
The investigation, conducted by the JTSB with assistance from the NTSB, examined flight data recorder (DFDR) records, air traffic control communications, and crew statements. Investigators analyzed the meteorological conditions, specifically focusing on the presence of cumulonimbus clouds and the strength of the jet stream at the time of the event. The investigation also reviewed cabin safety protocols, including the timing of seat belt sign illumination and the status of passenger seat belts during the descent.