What happened
A Sabena World Airlines DC-10-30 was operating a flight from Detroit, Michigan, to Boston, Massachusetts, while descending from flight level 410. As the aircraft passed through flight level 404, it encountered high-altitude windshear. The pilot reported large amplitude oscillations which prompted the request for descent.
Prior to initiating the descent, no announcement was made regarding seatbelt usage. During the upset, significant vibrations were felt by everyone on board. The turbulence caused passengers, flight attendants, and loose objects within the cabin to strike the ceiling. 12 people were injured, including eleven passengers and one flight attendant. Three of those injured required medical treatment.
The investigation
The investigation focused on the mechanical condition of the aircraft and the environmental factors encountered during the descent. The large amplitude oscillations noted by the pilot were identified as the primary driver of the cabin upset. No mechanical failure was cited as a cause for the oscillations.
Findings
Contributing factors included the high-altitude windshear and the lack of prior warning to occupants about fastening seatbelts before the descent began. The sudden nature of the turbulence prevented passengers from securing themselves in time.