Delays and safety in airline maintenance

Airline maintenance operations affect the potential for flight delays and can also affect flight safety if signals of technical problems are missed or misinterpreted. In this paper, we use a probabilistic risk analysis model, represented by an influence diagram, to quantify the effect of an airline's maintenance policy on delays, cancellations and in-flight safety. The model represents the leading edge (LE) sub-system of a commercial passenger jet and consists of three tiers: (1) a set of management decision variables (e.g. the level of qualification of maintenance personnel); (2) a ground model linking policy decisions and flight delays; and (3) an in-flight model, linking policy decisions, maintenance quality and flight safety. To illustrate this model, we use data adapted (for confidentiality reasons) from a study of an existing airline. Clearly, the LE devices of an airplane are not among the most safety-critical and the risk of an accident due to poor maintenance is extremely small, but non-zero. The same model can be used for other, more critical parts of the aircraft to support maintenance policy decisions in which the trade-off between delays and safety may be more pronounced.     

Improving aircraft safety and reliability by aircraft maintenance technician training

Aircraft maintenance is one of the primary causes or contributing factors in aircraft accidents. It is clear that proper training of Aircraft Maintenance Technicians (AMTs) will avoid failures, reduce maintenance related accidents, improve safety and reliability in aviation and provide recovery of the increasing demand to qualified AMTs for sustainability of the market growth. In this study, European Safety Agency (EASA) based AMT licencing system in EU states (and non-EU states implementing EASA rules) has been analysed and a training model developed in accordance with EASA Part-66 requirements and delivered by e-learning methods has been introduced. The analysis of the licensing process based on EASA regulations showed that this process was based on the candidate's demonstration of knowledge and acquisition of experience. The required experience depends on the training background of the candidate. Field exercise showed that developed e-learning training model, which overcomes the disadvantages of traditional face to face training models, succeeded to improve the attendees' theoretical knowledge level and when combined with the practical trainings given to AMT candidates in maintenance organisations during their experience periods, will be very successful in improving safety and reliability in aviation maintenance operations.     

Safety climate and the Theory of Planned Behavior: Towards the prediction of unsafe behavior

The present study is concerned with the human factors that contribute to violations in aviation maintenance. Much of our previous research in this area has been based on safety climate surveys and the analysis of relations among core dimensions of climate. In this study, we tap into mainstream psychological theory to help clarify the mechanisms underlying the links between climate and behavior. Specifically, we demonstrate the usefulness of Ajzen's (1991, 2001) Theory of Planned Behavior (TPB) to understanding violation behaviors in aircraft maintenance. A questionnaire was administered to 307 aircraft maintenance workers. Constructs measured by the survey included perceptions of management attitudes to safety, own attitudes to violations, intention to violate, group norms, workplace pressures, and violations. A model based on the TPB illustrated hypothetical connections among these variables. Path analyses using AMOS suggested some theoretically justifiable modifications to the model. Fit statistics of the revised model were excellent with intentions, group norms, and personal attitudes combining to explain 50% of the variance in self-reported violations. The model highlighted the importance of management attitudes and group norms as direct and indirect predictors of violation behavior. We conclude that the TPB is a useful tool for understanding the psychological background to the procedural violations so often associated with incidents and accidents.     

An investigation of the repetitive failure in an aircraft engine cylinder head

Cylinder head (CH) failures in aircraft piston engine may have serious or fatal consequences to the safety of the crew and the aircraft. Moreover, when failure becomes undoubtedly repetitive and critical resulting in loss of aircraft, destruction of properties, and first and foremost loss of human lives, the cause of the failure requires to be investigated using a scientific approach. Therefore, the aim of this study is to investigate and identify the root cause of a repetitive premature failure in an aircraft engine CH.The piston engine of the training aircraft Utva-75 has malfunctioned during the flight due to the cracking of its aluminum cast CH. It has been the second engine failure of this type of aircraft due to the cracking in the CH in a very short span of time. From the visual examination of the mating fracture surfaces, it has been possible to observe typical beach and ratchet marks indicating the occurrence of fatigue failure. The crack has initiated from multiple origins located on the inner flange fillet on the exhaust side of the CH. Further examinations by using scanning electron microscopy as well as energy dispersive spectroscopy and metallography have shown that the fatigue had promoted from pre-existing material defect due to a high concentration of shrinkage pores at the initiation crack site and can be most likely associated with the manufacturing process of casting. The stress analysis of the cylinder assembly, carried out by means of finite element analysis, has also confirmed that the crack origin was located at the most stressed area of the cylinder assembly i.e. on the inner flange fillet of the exhaust side of the CH.This case study, together with the other recently reported, has definitely confirmed the repetitive and therefore systematic problems with the CH of air cooled, horizontally opposed, aircraft piston engines.     

Trending of equipment inoperability for commercial aircraft

The Safety Performance Analysis System (SPAS) is a Web-based analytical tool, or rather a database system, that is being fielded by the Federal Aviation Administration (FAA). It is intended to provide the FAA’s Aviation Safety Inspectors (ASIs) with the means to evaluate and control appropriate surveillance levels for aircraft operators. The SPAS enables qualitative trend analysis to be performed at the national, regional, and district levels. This will permit the system to be more sensitive to particular areas of concern for a given region. For example, inspectors particularly desire a tool to help them recognize problems which are occurring in the fleet. Especially desirable is a tool that could do so automatically by searching for trends and alerting the relevant inspectors.The Service Difficulty Reporting (SDR) system, one of the SPAS databases, provides FAA inspectors with information related to aircraft equipment inoperability, such as in-service difficulties, malfunctions, and defects. The SDR data provide information for planning, directing, controlling, and evaluating certain assigned safety and maintenance programs. This paper presents previous SDR trending results for DC-9 operators with heterogeneous fleets, but now uses data from two specific operators with homogenous fleets consisting entirely of 737 aircraft. This new research is an extension of the previous SDR forecasting research, but now provides more meaningful information, as the DC-9 aircraft data were composed of numerous operators with mixed fleets and differing operating and maintenance policies. Multiple regression and neural network models are the principal two forecasting methods examined. A population modeling concept, or data grouping strategy, appears to be an effective technique for trending SDRs for operators of either heterogeneous and homogeneous fleets. The forecasting methods presented in this paper offer technical enhancements for SDR trending compared to the current qualitative method of visual observation of graphical plots.     

An analysis of maintenance failures at a nuclear power plant

In this paper, a study of faults caused by maintenance activities is presented. The objective of the study was to draw conclusions on the unplanned effects of maintenance on nuclear power plant (NPP) safety and system availability. More than 4400 maintenance history reports from the years 1992–1994 of Olkiluoto BWR NPP were analysed together with the maintenance personnel. The human action induced faults were classified, e.g. according to their multiplicity and effects. This paper presents and discusses the results of a statistical analysis of the data. Instrumentation and electrical components appeared to be especially prone to human failures. Many human failures were found in safety related systems. Several failures also remained latent from outages to power operation. However, the safety significance of failures was generally small. Modifications were an important source of multiple human failures. Plant maintenance data is a good source of human reliability data and it should be used more in the future.     

Process burner and combustion system hazards: 10 key issues that save lives

Burner and combustion safety is crucial for the safe operation of fuel-fired heaters and boilers at process industry facilities. This paper discusses 10 of the most common burner and combustion system hazards that impact the safe operation of combustion equipment. The paper includes a discussion of three burner related explosion incidents that occurred at plants and how to avoid them. Strategies are also presented for training of maintenance and operations personnel on hazard recognition and avoidance. A protocol for walking down equipment prior to light offs is also presented as an extra safety step.     

A copula-based quantified airworthiness modelling for civil aircraft engines

The aircraft engine serves as the core system of an aircraft and operates under extreme conditions, requiring high reliability and absolute safety. The design, manufacturing, and after-sales services of aircraft engines are complex processes. To ensure safety and performance, maintenance checks are performed periodically and hierarchically throughout the engine’s life-cycle. Among these checks, shop visit (SV) heavy maintenance checks play a crucial role but are also costly, especially when they occur unexpectedly and unplanned. Analysis of the maintenance logbook, recording aviation operations, reveals a significant occurrence of unplanned SVs, which may be attributed to the existing maintenance policy based on a single time-definition. To address this issue, this paper seeks to establish a novel approach to quantifying airworthiness through copula modelling, which combines two time-definitions: the flying hour (FH) and the flying cycle (FC). This approach is unique in the aviation industry. By employing the Gumbel copula with the generalized extreme value (GEV) distribution as the marginal distribution, and utilizing non-parametric association measurement parameter estimation, the quantified airworthiness of civil aircraft engine fleets across multiple product lines can be effectively modeled. This research provides valuable insights into optimizing maintenance policies and enhancing the reliability and safety of aircraft engines.     

The use of maintenance indicators to evaluate the effects of maintenance programs on NPP performance and safety

Nuclear Power Plants (NPPs) under commercial operation are under continuous demand to meet higher levels of performance and safety by NPP owners, regulatory authorities and the public in general. Maintenance plays an important role in achieving such a goal, therefore, many programs are being conducted in order to improve their effectiveness. A common link between these programs is the necessity to evaluate how maintenance affects NPP performance and safety. This paper presents the foundation of a methodology for a maintenance evaluation program based on maintenance indicators and how it is applied to monitoring the effectiveness of the maintenance at the Cofrentes NPP. The methodology is general and might be applied in other fields of industrial engineering, particularly in those activities which devote many resources to maintain plant equipment, and also in those with less but very critical maintenance.     

Aircraft impact analysis of nuclear safety-related concrete structures: A review

Safety-related nuclear structures, including concrete nuclear containment vessels, constructed before September 11, 2001, were not purposely designed to resist any impact loading greater than a light aircraft crash. Since 2001, safety of nuclear facilities against a deliberate or accidental large civilian aircraft impact has drawn much attention worldwide. However, current design guides for nuclear structures provide limited information on analysis methodologies for such aircraft impact. This document presents basic general knowledge required to analyze concrete structures for an aircraft impact and provides a summary of available numerical and experimental investigations that may be used to benchmark an aircraft impact simulation. The methodologies available for an aircraft impact analysis are overviewed with an emphasis on structural damage analysis. Constitutive models used for concrete, reinforcing steel, and composite materials are addressed in this paper.     

Condition, safety and cost profiles for deteriorating structures with emphasis on bridges

After an enormous investment in construction of highway networks undertaken in the second half of the 20th century, the highway networks of most European and North American countries are now completed or close to completion. As a result, the need in funding changed from building new highway structures to repair, rehabilitation, and replacement the existing ones. In this paper, a model for analyzing the evolution in time of probabilistic performance indicators of existing structures, in terms of condition, safety, and cost under no maintenance, preventive maintenance, and essential maintenance, is presented. This model integrates the current practice in bridge management systems based on visual inspections (condition index) with structural assessment (safety index) during the lifetime of existing structures. The proposed model allows the consideration of uncertainties in the performance deterioration process, times of application of maintenance actions, and in the effects of maintenance actions on the condition, safety, and life-cycle cost of structures by defining all parameters involved in the model as random variables. Interaction between condition and safety profiles is defined through probabilistic and deterministic relations. The probabilistic characteristics of the condition, safety, and cost profiles of deteriorating structures are computed by Monte-Carlo simulation. Several realistic examples, based on data on highway bridge components gathered in the United Kingdom, are presented.     

Hierarchical Colored Timed Petri Nets for Maintenance Process Modeling of Civil Aircraft

Civil aircraft maintenance process simulation model is an effective method for analyzing the maintainability of a civil aircraft. First, we present the Hierarchical Colored Timed Petri Nets for maintenance process modeling of civil aircraft. Then, we expound a general method of civil aircraft maintenance activities, determine the maintenance level for decomposition, and propose the methods of describing logic of relations between the maintenance activities based on Petri Net. Finally, a time Colored Petri multi-level network modeling and simulation procedures and steps are given with the maintenance example of the landing gear burst tire of a certain type of aircraft. The feasibility of the method is proved by the example.     

Optimal specialization of a maintenance workforce

This article develops an analytical method for determining an optimal specialization strategy for a maintenance workforce. The method assumes that maintenance tasks are generated by a system of statistically identical machines that experience random malfunctions and require periodic service. The impact of alternative workforce structures on system performance is evaluated with a queueing network model. Markov decision analysis is employed to determine an optimal assignment of maintenance personnel to pending tasks as the network status varies over time. A linear programming algorithm is derived to enable simultaneous optimization of specific assignment decisions and the overall workforce structure. A manufacturing example demonstrates the applicability of the method to many industrial contexts. The method is also applied to the problem of maximizing military aircraft sortie generation subject to a constraint on maintenance personnel expenditure.     

Operational reliability assessment of an aircraft environmental control system

The aircraft environmental control system (ECS) is composed of several non-identical and non-dedicated subsystems working as warm-cold standby subsystems. Also, their state transition times are arbitrary distributed. This paper presents a flow-graph-based method to calculate time-to-failure data and failure probability of the ECS. The obtained data from the model may be used for maintenance optimization that employs the failure limit strategy for ECS. The model incorporates detectable failures such as hardware failures, critical human errors, common-cause failures, maintenance categories, and switch activation methods. A numerical example is also presented to demonstrate the application of the model.     

Developing countries and the aircraft industry: match or mismatch?

For many industrially developing countries, technology transfer is seen as a road towards technological and economic development. Indonesian experiences with the aircraft industry suggest that the transfer of technology in this sector is extremely difficult, and even if technology is actually transferred it does not necessarily lead to a viable industry. To determine the key elements for a successful transfer of technology, research was undertaken with a focus on the process of technology transfer at the operational level in industrially developing and developed countries. The research revealed that many technology transfer projects do not or, at best, only marginally contribute to technological development. It also showed that the aircraft industry, and possibly other industries as well, might be better suited to specific countries. To avoid making investments in industries that will inevitably not be competitive, industrially developing countries should be careful when deciding which types of industry to foster.     

Fatigue in aerostructures--where structural health monitoring can contribute to a complex subject

An overview of the aircraft design and maintenance process is given with specific emphasis on the fatigue design as well as the phenomenon of the ageing aircraft observed over the life cycle. The different measures taken to guarantee structural integrity along the maintenance process are addressed. The impact of structural health monitoring as a means of possibly revolutionizing the current aircraft structural monitoring and design process is emphasized and comparison is made to jet engines and helicopters, where health monitoring has already found the respective breakthrough.     

虚实融合的协同工作环境CAR-CA工程技术研究进展

采用虚实融合和协同工作技术进行大型装备的设计论证和辅助拆装维护是工程科技发展的一个新方向。面向我国自行设计生产商用大飞机的需求,在863计划支持下,正在研制用于驾驶舱布局设计和飞机关键部件辅助拆装维护的虚实融合协同工作环境CAR—CA（collaborative augmented reality for commercial aircraft design ＆ maintenance）。概要介绍CAR—cA的工程技术研究进展,包括体系结构、系统组成、关键技术研究和系统的应用前景等。     

Maintenance free operating period – an alternative measure to MTBF and failure rate for specifying reliability?

The paper analyses the concept of maintenance free operating period (MFOP), the reliability requirement driven by the Ministry of Defence (UK) for the next generation of future aircraft to be included in the fleet. Since the traditional reliability requirement MTBF (mean operating time between failure) has several drawbacks, the immediate reaction would be to analyse the credibility of the new measure MFOP against MTBF. The paper discusses various issues associated with MFOP. Two mathematical models are developed to predict the maintenance free operating period survivability (MFOPS), one using mission reliability approach and the other using alternating renewal theory. The paper also analyses cost implications of MFOP to the customer and to the producer.     

Aircraft parameter estimation — A tool for development of aerodynamic databases

With the evolution of high performance modern aircraft and spiraling developmental and experimental costs, the importance of flight validated databases for flight control design applications and for flight simulators has increased significantly in the recent past. Ground-based and in-flight simulators are increasingly used not only for pilot training but also for other applications such as flight planning, envelope expansion, design and analysis of control laws, and handling qualities investigations. Most of these demand a high-fidelity aerodynamic database representing the flight vehicle. System identification methodology, evolved over the past three decades, provides a powerful and sophisticated tool to identify from flight data aerodynamic characteristics valid over the entire operational flight envelope. This paper briefly presents aircraft parameter estimation methods for both stable and unstable aircraft, highlighting the developmental work at the DLR Institute of Flight Mechanics. Various aspects of database identification and its validation are presented. Practical aspects like the proper choice of integration and optimization methods as well as limitations of gradient approximation through finite-differences are brought out. Though the paper focuses on application of system identification methods to flight vehicles, its use in other applications, like the modelling of inelastic deformations of metallic materials, is also presented. It is shown that there are many similar problems and several challenges requiring additional concepts and algorithms.     

Failure analysis of an aircraft engine cylinder head

The piston engine of the training aircraft malfunctioned during the flight due to the cracking of its cylinder head (CH), which is manufactured from an aluminum casting alloy. Based on the fractographic examination of the mating fracture surfaces, the characteristic ratchet and beach marks were observed indicating the occurrence of fatigue failure. The crack was initiated from multiple origins located on the inner flange fillet on the exhaust side of the CH. The metallography examination has shown that the fatigue was promoted from pre-existing material defect due to an elevated presence of shrinkage pores at the crack initiation zone and was most likely associated with the manufacturing process of casting. The finite element (FE) method, utilized to determine the stress state of the CH subjected to gas pressure, also confirmed that the crack origin was located at the most stress area.