Fault Tolerant Control of Large Civil Aircraft

Ensuring flight safety is of utmost importance in the aviation industry. According to reports from the International Civil Aviation Organization, there were a total of 850 accidents recorded between 2012 and 2022, resulting in 3309 fatalities. In addition to the human factors, the key factors identified in the flight accidents include the mechanical failures, faulty components, and extremely challenging perturbations (such as turbulence and wind gust). To enhance safety and reliability, modern aircraft primarily employ redundant configurations. An invaluable technology for mitigating the adverse effects caused by failures is Fault Tolerant Control (FTC), which can detect, isolate and accommodate the faults in real-time and therefore maintain the continued safe operation of the flight.

This chapter introduces a novel approach to enhance the reliability and safety of modern commercial aircraft through convex optimization-based fault-tolerant control (CO-FTC) for dissimilar redundant actuation systems (DRAS). The DRAS, which includes a hydraulic actuator (HA) and electro-hydrostatic actuator (EHA), is briefly introduced and modeled in a state space framework with gradual faults. In order to improve the flight safety with gradual DRAS faults, a convex optimization-based fault-tolerant control (CO-FTC) strategy optimizes the control gain matrix via linear matrix inequalities (LMIs) to ensure stability despite faults. Unlike traditional methods, a novel subsystem-based technique is employed to enhance system performance under faults. Comprehensive case studies illustrate the necessity of fault tolerance, validating the CO-FTC strategy’s efficacy. Comparative analysis of simulation results demonstrates its robustness and effectiveness in contrast to existing methods.

This chapter introduces an approach for fault-tolerant control (FTC) in a dissimilar redundant actuation system (DRAS) comprising hydraulic (HA) and electro-hydrostatic (EHA) actuators. DRAS, prone to multiple gradual faults due to prolonged service and harsh conditions, can degrade system performance, inducing parameter uncertainty and eventual drift into a fault state. To mitigate this, historical gradual fault statistics and a fault mode probability factor (FMPF) are used to amend the uncertain system model. The FTC strategy based on FMPF is implemented for the amended model, with updates to system estimation and linear quadratic regulator (LQR) at the sampling period’s conclusion. Simulations of DRAS under various faults validate the efficacy of this approach.

The industry trend in aircraft actuation systems towards more electric aircraft (MEA) is exemplified by the Dissimilar Redundant Actuation System (DRAS), which comprises a hydraulic actuator (HA) and an electro-hydrostatic actuator (EHA). This chapter delves into the performance degradation of the DRAS when confronted with system malfunctions. The focal point is on enabling active switching of the actuation system from HA to EHA, ensuring both reliability and efficient control. The research introduces a pioneering Active Fault-Tolerant Controller (AFTC) that draws from Performance Degradation Reference Models (PDRM). These PDRMs are established by deciphering the fundamental rules governing the performance degradation of the DRAS. This is achieved by analyzing the impact of fault severity on the system’s root locus. The resulting PDRMs are formulated as a sequence of second-order functions. Consequently, an Intelligent Matching Algorithm (MA) is devised, centered around the dominant closed-loop poles. Leveraging this algorithm, a set of Adaptive Fuzzy Controllers (AFC) is formulated. These controllers are rooted in the proposed PDRMs and the Intelligent MA, enabling the DRAS to maintain a certain level of fault-tolerant capability even under performance-degraded conditions. The efficacy of the outlined Active Fault-Tolerant Control scheme is substantiated through an array of extensive simulation results.

This chapter introduces a novel approach to fault tolerant control (FTC) for aircraft models with partial faults in actuators and sensors. The proposed technique utilizes a variable-order observer-based reconfigurable scheme. The aircraft’s hybrid states, which consist of both observer states and normal states, are utilized in the reconfiguration of the optimal fault tolerant control gain. This reconfiguration is carried out using the linear quadratic regulator (LQR) technique, specifically tailored to address certain fault conditions. The switching mechanism has been devised with the purpose of achieving seamless transitions between various control gains. The verification of the convergence of the observer and the effectiveness of the fault tolerant controller is conducted using numerical simulation.

Aircraft longitudinal control is the most important actuation system and its failures would lead to cata-strophic accident of aircraft. This chapter proposes an active fault-tolerant control (AFTC) strategy for civil aircraft with different numbers of failed elevators. To enhance the performance of the fault-tolerant flight control system and effectively utilize the control surface, a trimmable horizontal stabilizer (THS) is considered to generate extra pitch moment. A suitable switching mechanism with a performance improvement coefficient is proposed to determine when it is worthwhile to utilize the THS. Furthermore, the AFTC strategy is detailed using model following techniques and the proposed THS switching mechanism. A basic fault-tolerant controller is designed to ensure the stability of the longitudinal control system and acceptable performance degradation under partial elevator failure. The proposed AFTC is applied to a Boeing 747–200 numerical model, and simulation results validate the effectiveness of the proposed AFTC approach.

This chapter introduces a mathematical model and an adaptive flight controller designed to account for structural damage occurring in the horizontal stabilizer of an aircraft. The aerodynamic derivatives are determined by assessing the rate of structural damage sustained by the horizontal stabilizer. We establish a failure model that takes into consideration the aerodynamic derivatives resulting from the damaged horizontal stabilizer, and we adjust the efficiency coefficients based on wind tunnel experiments. To ensure active fault tolerance in the event of horizontal stabilizer damage, we devise an adaptive fault-tolerant control law using parameter estimation. The simulation and experimental results consistently demonstrate that the proposed model and adaptive fault-tolerant controller yield superior performance when the horizontal stabilizer has incurred damage.

In this chapter, some conclusions and discussions are provided as the end of the book, and some future work is also presented.