System health diagnosis serves as an underpinning enabler for enhanced safety and optimized maintenance tasks in complex assets. In the past four decades, a wide-range of diagnostic methods have been proposed, focusing either on system or component level. Currently, one of the most quickly emerging concepts within the diagnostic community is system level diagnostics. This approach targets in accurately detecting faults and suggesting to the maintainers a component to be replaced in order to restore the system to a healthy state. System level diagnostics is of great value to complex systems whose downtime due to faults is expensive. This paper aims to provide a comprehensive review of the most recent diagnostics approaches applied to hardware systems. The main objective of this paper is to introduce the concept of system level diagnostics and review and evaluate the collated approaches. In order to achieve this, a comprehensive review of the most recent diagnostic methods implemented for hardware systems or components is conducted, highlighting merits and shortfalls.

No abstract

Abstract Auxiliary Power Units (APUs) are a major driver of maintenance on civil aircraft. However, experimental data and performance simulations are rarely seen in public domain literature. While there is recourse to aircraft engine experience, this does not address the loading and the failure modes of an APU. The aim of this work is to significantly add to the literature, by experimentally investigating a Boeing 747 APU, collecting data under various power settings and ambient conditions, and using this data to calibrate a simple simulation model. This simulation model will subsequently be used to explore failure modes in the APU and hence what sensors may be needed for health monitoring purposes in future work. In this paper, a Boeing 747 APU rig development process and the adopted testing strategy are presented. The rig is validated through a process that includes uncertainty analysis, repeatability tests, consistency tests and comparison of the collected data with the calibrated simulation model. The results from the rig's validation indicate that the data collected from the APU is independent of its running time or the order of loading cycles imposed on it, i.e. the results are path independent. The rotational speed shows a slightly increasing trend when the extracted power rises, and this affects the APU thermodynamic characteristics. This work has resulted in a calibrated simulation model that will be further used in examining fault mode scenarios, as injecting these directly into the rig is seen as high risk.

This paper proposes a diagnostic technique that can predict component degradation for a number of complex systems. It improves and clarifies the capabilities of a previously proposed diagnostic approach, by identifying the degradation severity of the examined components, and uses a 3D Principal Component Analysis approach to provide an explanation for the observed diagnostic accuracy. The diagnostic results are then used, in a systematic way, to influence maintenance decisions. Having been developed for the Auxiliary Power Unit (APU), the flexibility and power of the diagnostic methodology is shown by applying it to a completely new system, the Environmental Control System (ECS). A major conclusion of this work is that the proposed diagnostic approach is able to correctly predict the health state of two aircraft systems, and potentially many more, even in cases where different fault combinations result in similar fault patterns. Based on the engineering simulation approach verified here, a diagnostic methodology suitable from aircraft conception to retirement is proposed.

Gas turbine engines include a plethora of rotating modules, and each module consists of numerous components. A component’s mechanical fault can result in excessive engine vibrations. Identification of the root cause of a vibration fault is a significant challenge for both engine manufacturers and operators. This paper presents a case study of vibration fault detection and isolation applied at a Rolls-Royce T-56 turboprop engine. In this paper, the end-to-end fault diagnosis process from starting system faults to the isolation of the engine’s shaft that caused excessive vibrations is described. This work contributes to enhancing the understanding of turboprop engine behaviour under vibration conditions and highlights the merit of combing information from technical logs, maintenance manuals and engineering judgment in successful fault diagnosis.