The National Transportation Safety Board is an independent Federal agency dedicated to promoting aviation, railroad, highway, marine, pipeline, and hazardous materials safety. Established in 1967, the agency is mandated by Congress through the Independent Safety Board Act of 1974 to investigate transportation accidents, determine the probable causes of the accidents, issue safety recommendations, study transportation safety issues, and evaluate the safety effectiveness of government agencies involved in transportation. The Safety Board makes public its actions and decisions through accident reports, safety studies, special investigation reports, safety recommendations, and statistical reviews.
Abstract: This report explains the inadvertent deployment of the MD-11 airplane's leading edge wing slats while the airplane was in cruise flight, about 950 nautical miles south of Shemya, Alaska, on April 6, 1993. Safety issues in the report focused on the inadequate design of the flap/slat actuation handle, the inadvertent extension of the leading edge wing slats, the longitudinal stability of the airplane during the pitch upset, the pilot-induced oscillations that can occur during recovery, the premature deterioration of the seat cushion fire-blocking material, and the inability of the material to provide the required seat cushion fire protection on transport-category airplanes. Safety recommendations on these issues were made to the Federal Aviation Administration.
On April 6, 1993, at 0110 Hawaiian Standard Time, China Eastern Airlines flight 583, a McDonnell Douglas MD-11, Chinese registration B-2171, a scheduled international passenger flight from Beijing, China, to Los Angeles, California, with an intermediate stop in Shanghai, China, had an inadvertent deployment of the leading edge wing slats while in cruise flight, approximately 950 nautical miles south of Shemya, Alaska. The autopilot disconnected, and the captain was manually controlling the airplane when it progressed through several violent pitch oscillations and lost 5,000 feet of altitude. The captain regained stabilized flight, declared an emergency because of passenger injuries, and diverted to the U.S. Air Force Base, Shemya, Alaska. Of the 235 passengers and 20 crewmembers aboard the airplane, 2 passengers were fatally injured, and 149 passengers and 7 crewmembers received various injuries. The airplane did not receive external structural damage, but the passenger cabin was substantially damaged.
The National Transportation Safety Board determines that the probable cause of this accident was the inadequate design of the flap/slat actuation handle by the Douglas Aircraft Company that allowed the handle to be easily and inadvertently dislodged from the UP/RET position, thereby causing extension of the leading edge slats during cruise flight. The captain's attempt to recover from the slat extension, given the reduced longitudinal stability and the associated light control force characteristics of the MD-11 in cruise flight, led to several violent pitch oscillations.
Contributing to the violence of the pitch oscillations was the lack of specific MD-11 pilot training in recovery from high altitude upsets, and the influence of the stall warning system on the captain's control responses. Contributing to the severity of the injuries was the lack of seat restraint usage by the occupants.
The safety issues in this report focused on the inadequate design of the flap/slat actuation handle on the MD-11 airplane, the inadvertent extension of the leading edge wing slats, the longitudinal stability of the MD-11 during the pitch upset, and the pilot-induced oscillations that can occur during the recovery. Also discussed is the premature deterioration of the seat cushion fire-blocking material and the inability of the material to provide the required seat cushion fire protection on transport-category airplanes.