A study of flap torque tube design and installation

Abstract Transmission torque tubes are widely used devices to transmit the mechanical power for wing high lift systems on civil aircraft. It connects the power drive unit to the actuator. The torque tube transmits torque from the power drive unit to the actuator, which in turn drives the flap surfaces. Therefore, if the torque tube is not properly installed, there is a potential risk of loss of transmission. In severe cases, this hazard results in the torque tube no longer being restrained and can be disconnected. It will trigger the asymmetric detection protection of the control surface during the operation of the flap system, resulting in the closure of the flap system with the EICAS message FLAP FAULT. The flap system will be locked in its position until the aircraft landing. This article describes an incident of a flap torque tube disconnection on a type of civil aircraft. It also demonstrates the function, design architecture, and installation method of the torque tube and analyzes for durability and reliability of the torque tube. In addition, it illustrates the protection system of the aircraft caused by the torque tube disconnection. Then, it analyzes the torque tube installation procedure, inspection method, and related precautions. Besides, it analyzes other potential failure modes. Finally, the future research directions drive further technological development implementing torque tube status monitors for the whole life cycle.