Alaska Airline 261 Torque Tube Fracture

On the afternoon of January 31, 2000, a McDonnell Douglas MD-83 crashed into the Pacific Ocean off the coast of California. The accident was the result of maintenance actions that lead to a wear failure of the acme nut threads in the horizontal trim system. However, for complete separation of the tail, the quill shaft (torque tube) in the jackscrew also had to fracture. The titanium torque tube normally transmits torque from the electric motor on top of the jackscrew to the screw but was unusually loaded after the separation of the nut threads. A discussion of the tests and analysis to determine the failure mode will be presented.