Diagnostic Method for a Landing Gear and Doors Actuation System Based on a State Machine Control Algorithm

A Landing Gear Control and Actuation System (LGCAS) is one of the most complex aircraft systems. Due to the large landing gear masses and high performance requirements, aircraft hydraulic power with multiple hydraulic actuators and valves is used to provide system dynamic. LGCAS also requires a electrical source of energy for the electro-mechanical components, sensors and electronic control unit. For many years, correct fault isolation in a complex kinematic system, such as an aircraft landing gear actuation system, has been a great challenge with limited success. The fault isolation design challenge rests on the fact that landing gear control and actuation system has many so called “passive” components, whose basic function cannot be continuously monitored without additional sensors, transducers, and designated health monitoring equipment. Driven by a philosophy that adding any nonessential component or system on the aircraft will increase system complexity, weight, and cost, this article is considers a mathematical algorithm which can be applied on the existing LGCAS to enhance the onboard diagnostic and fault isolation process. Aircraft landing gear actuation can be considered as a sequence of events where the control algorithm can be implemented as a state machine. As such, a state machine vector can be used to narrow down a number of “passive” components whose single failure cannot be detected. From the reduced number of landing gear control and actuation system components, further mathematical algorithm has been developed to identify and isolate a single failed component.