Airworthiness of aircraft. Part 2. Monte Carlo simulation of fleet performance history

A computer program using the Monte Carlo technique to simulate aircraft performance in fleet operation (modelled in part 1 of this paper) is described. The technique follows the variation in the performance capability of each aircraft in the fleet over its service life. Arbitrary distributions or values can be specified for the input parameters of the stochastic model; in addition, the effect of certification and inspection procedures can also be studied. The output of the simulation includes the performance history of any specific aircraft, fleet performance distribution and statistics (in-service as well as just after overhauls) and the incident rates. Such a simulation of the single-engine climb gradient of a twin-engined turboprop aircraft leads to the following conclusions for a typical medium-haul airline fleet of 15 aircraft. The fleet mean rather than the standard deviation is generally sensitive to changes in the operating conditions. The time required for the fleet to relax from its new state to near in-service equilibrium conditions is found to increase from 4 months when maintenance is perfect to about 3 years when the maintenance efficiency (a measure of the extent of performance recovery in relation to new aircraft) is 25 %. It is found that the gradient considered acceptable at entry into service strongly influences the incident rates, but that the actual testing procedure adopted for clearing aircraft, such as single test, two-best-of-four etc., has hardly any effect. The incident rates are strongly affected by the maintenance efficiency and the flight scatter, moderately by the mean airframe and engine deterioration and the time interval between overhauls, and marginally by propeller deterioration. It is concluded that current airworthiness codes for engine-out take-off climb drawn up in the fifties are today generally conservative because of improved engine reliability, but may still be necessary for engines going through their ‘learning’ period.     

噪声适航标准严格化趋势探究

国际民航组织制定了航空器噪声审定的建议标准—国际民航公约附件16第I卷“航空器噪声”,把航空器按噪声水平分成第一、二、三、四章标准的飞机（即CCAR-36中的第一、二、三、四阶段飞机）,要求飞机在投入运营之前,必须进行并通过飞机噪声适航合格审定,否则不予颁发适航合格证。同时,国际民航组织正在研究更严格的噪声标准。预计到2016年,大型客机适航噪声将比第四阶段噪声限制低18 EPN dB以上。为使中国民用航空器的设计制造满足国际通行的噪声标准,需研究更新后的噪声审定标准。     

High cycle fatigue in aircraft gas turbines—an industry perspective

The largest single cause of component failures in modern military aircraft gas turbine engines is high cycle fatigue (HCF), exceeding the number attributed to low cycle fatigue, corrosion, overstress, manufacturing processes, mechanical damage, and materials. The HCF problem is a pervasive one, affecting all engine sections and a wide range of materials. In addition to the impact on engine component reliability, HCF problems cause significant economic impacts through field inspection and maintenance actions, and reduced readiness reliability. This paper presents an overview, from an industry perspective, of the current, highly empirical approach for assessing the HCF capability. Complicating factors that must be addressed which affect engine HCF material capability are also described. Future directions which would improve the current approach are outlined, emphasizing incorporation of fracture mechanics. Technical challenges which must be addressed to successfully implement use of fracture mechanics for HCF are described, and areas of research recommended.     

Airworthiness of aircraft. Part 1. A stochastic model

It is argued that a stochastic approach to airworthiness analysis is necessary because of the inherent random variations in aircraft performance. It is then shown that the history of any performance variable in fleet service is best regarded as a ‘stochastic corrective process’, characterised by slow deterioration punctuated by rapid improvements at overhauls. Considering specifically the engine-out take-off climb performance of an aircraft, a model is proposed by taking into account gradient changes due to the deterioration of airframe, engine and propeller (if present), the frequency and effectiveness of overhauls, and the occurrence of deviations in the gradient achieved on any flight from the true capability of the aircraft. In analysing the effect of overhauls a distinction is made between maintenance by rectification and by replacement. In the model proposed a total of 14 parameters govern the probability distribution of the achieved gradient in fleet history, and consequently also the incident rate during take-off climb.     

Training of the maintenance personnel to prevent failures in aircraft systems

The aircraft maintenance process plays a vital role in aviation safety. The quality of the maintenance process and the qualifications of the aircraft maintenance personnel are important factors in the safety of aircraft.In this study the aircraft maintenance training model has been developed by especially taking in to account the EASA Part 66 regulations. The progression of the aircraft maintenance personnel training was investigated and suggestions to improve training process were given so as to prevent failures in aircraft systems.     

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.     

Rotational torsion fatigue failure of an engine driven fuel pump coupling

Between 2005 and 2007 serious flight safety concerns arose when a small fleet of single engine basic trainer aircraft experienced five critical failures of engine driven fuel pump (EDFP) couplings, and a further instance of a cracked coupling. Consequent investigations showed that the coupling fractures were likely to have been caused by a combination of reverse torsional loading and bending. Engine ground runs were then carried out to evaluate linear and torsional engine vibration levels in the drive train affecting the fuel pumps. Analysis of the vibration data indicated that engines, which had caused pump‐coupling failures exhibited high‐amplitude torsional vibration at certain power settings. The excessive vibration level was eventually attributed to detuning of the crankshaft counterweight dampers. This investigation resulted in a change to the maintenance practises on the aircraft in question and no fuel pump failures have occurred since December 2008.     

Accident-precipitating factors for crashes in turbine-powered general aviation aircraft

General aviation (14CFR Part 91) accounts for 83% of civil aviation fatalities. While much research has focused on accident causes/pilot demographics in this aviation sector, studies to identify factors leading up to the crash (accident-precipitating factors) are few. Such information could inform on pre-emptive remedial action. With this in mind and considering the paucity of research on turbine-powered aircraft accidents the study objectives were to identify accident-precipitating factors and determine if the accident rate has changed over time for such aircraft operating under 14CFR Part 91.The NTSB Access database was queried for accidents in airplanes (<12,501 lb) powered by 1–2 turbine engines and occurring between 1989 and 2013. We developed and utilized an accident-precipitating factor taxonomy. Statistical analyses employed logistic regression, contingency tables and a generalized linear model with Poisson distribution.The “Checklist/Flight Manual Not Followed” was the most frequent accident-precipitating factor category and carried an excess risk (OR 2.34) for an accident with a fatal and/or serious occupant injury. This elevated risk reflected an over-representation of accidents with fatal and/or serious injury outcomes (p < 0.001) in the “non-adherence to V Speeds” sub-category. For accidents grouped in the “Inadequate Pre-Flight Planning/Inspection/Procedure” the “inadequate weather planning” sub-category accounted (p = 0.036) for the elevated risk (OR 2.22) of an accident involving fatal and/or serious injuries. The “Violation FARs/AIM Deviation” category was also associated with a greater risk for fatal and/or serious injury (OR 2.59) with “Descent below the MDA/failure to execute the missed approach” representing the largest sub-category. Accidents in multi-engine aircraft are more frequent than their single engine counterparts and the decline (50%) in the turbine aircraft accident rate over the study period was likely due, in part, to a 6-fold increased representation of single engine airplanes.In conclusion, our study is the first to identify novel precursive factors for accidents involving turbine aircraft operating under 14CFR Part 91. This research highlights areas that should receive further emphasis in training/recurrency in a pre-emptive attempt to nullify candidate accident-precipitating factor(s).     

我国航空用变形钛合金材料

钛合金材料作为一种20世纪中叶出现并发展起来的新兴结构材料,因其具有优异的耐腐蚀性、高的比强度以及无磁性等一系列独特的优点,在航空航天等高端工业部门获得了广泛应用,目前飞机机体结构中的隔框、大梁、起落架以及航空发动机压气机匣、轮盘、叶片等承力部件大量使用钛合金材料制造。在上世纪60年代,美国、英国、前苏联等工业发达国家就已经在飞机及航空发动机制造中大量使用钛合金材料。我国钛合金材料在航空工业中的应用起步较晚,上世纪80年代开始才陆续在飞机及航空发动机制造中少量使用钛合金材料,但是进入21世纪之后,我国航空工业钛合金材料的应用水平大幅度提升。对我国目前已经进入工业化生产并在航空工业中获得工程化应用的变形钛合金材料进行了系统阐述。     

Anomaly detection of aircraft lead-acid battery

The lead-acid battery has been widely used in various fields. In civil aviation aircraft, it plays a vital role in the power system to maintain normal operation during the flight mission. Thus, an effective abnormal detection system for monitoring and diagnosing the status of aircraft lead-acid battery is essential to ensure its safety and reliability. This paper aims to effectively identify aircraft battery faulty using unsupervised anomaly detection techniques. It introduces state-of-the-art anomaly detection algorithms and evaluates their performance on a large real civil aviation battery data. The experimental results show that the latest isolation-based anomaly detectors, iForest and iNNE, have outstanding performance on this task and have promising applicability as efficient methods for guaranteeing the lead-acid battery quality and reliability in civil aviation aircraft.     

涡扇发动机边线噪声预测研究

随着飞机适航审定关于噪声要求的逐年提高,预测部件飞行噪声声压级可以为飞机的适航审定工作提供依据,也可以为发动机的减噪设计提供参考。通过对发动机部件噪声进行预测,可以有效确定发动机的部件特性。以核心机噪声为突破口,通过对发动机核心机的静态噪声进行预测,然后经过从静态到飞行状态相关映射因素声源移动效应、声衰减等的修正,最后得到飞机在边线时的噪声值。同时可以用文中的方法预测其他部件的噪声值,整合预测出整机的噪声,可作为适航审定的依据,从而大量减少适航审定过程的投入成本。     

A Critical Review of Laser Shock Peening of Aircraft Engine Components

Many aviation accidents are caused by the failure of aircraft engine components, and engine blades are especially vulnerable to high-cycle fatigue fracture in severe working environments as well as to impact damage caused by foreign objects. To address this problem, the United States took the lead and has been successful in implementing laser shock peening (LSP) as a surface treatment for aircraft engine components to enhance their fatigue performance. This review provides an overview of the development of LSP for use in treating aircraft engine components over the past three decades, with a brief introduction to the development of high-energy pulsed lasers for LSP. A particular focus of this review is on the limitations and challenges associated with the application of LSP for treating critical aircraft engine components. It is hoped that this review serves as a reference for future research and development that can lead to better performance of these components.     

Aspects of TBC service experience in aero engines

The frame conditions to apply advanced materials technologies in aero engines are envisaged from view point of an aircraft operator and performer of allocated maintenance repair and overhaul activities. Main targets are the reliable operation of the parts, the steady ecological improvement during operation and the reduction on overall cost per flight hour based on increased knowledge. The application of Thermal Barrier Coatings (TBCs) may contribute to reach these goals. They may – for example – add to optimised operation by reducing fuel consumption and by protecting important engine parts. The principles of a long term engine parts operation and repair philosophy are outlined to clarify the property requirements for reliable engine operation. Typical TBC‐protected components within actually operated civil aero engines are described. Silicate deposition on a HTP Blade and erosive attack of TBC is introduced exemplarily. A repair sequence to counteract surface degradation is introduced.     

飞越适航噪声时域信号预测方法研究

以往对发动机有效感觉噪声级的预测研究是通过1/3倍频程谱进行计算,从而得到发动机地面预测有效感觉噪声级,而使用时域噪声数据进行发动机有效感觉噪声级预测的研究相对较少。研究了飞机起飞飞越过程中的噪声传播特性的计算方法,使用该方法来模拟计算飞机一台发动机在起飞飞越过程中地面飞越噪声测量点接收到的时域噪声信号数据。根据ANP数据库数据计算飞机起飞飞越航迹,使用声线法计算使用某时刻噪声声压信号传递的路程和时间,根据飞机速度方向与飞越地面噪声测量点的角度来确定该时刻噪声信号的最大声压值,最后得出飞机发动机在起飞飞越过程中部分时间内地面噪声测量点接受的时域信号数据,对飞机噪声适航审定提供一定的理论依据。     

Two-dimensional extreme distribution for estimating mechanism reliability under large variance

The effective estimation of the operational reliability of mechanism is a significant challenge in engineering practices, especially when the variance of uncertain factors becomes large. Addressing this challenge, a novel mechanism reliability method via a two-dimensional extreme distribution is investigated in the paper. The time-variant reliability problem for the mechanism is first transformed to the time-invariant system reliability problem by constructing the two-dimensional extreme distribution. The joint probability density functions (JPDFs), including random expansion points and extreme motion errors, are then obtained by combining the kernel density estimation (KDE) method and the copula function. Finally, a multidimensional integration is performed to calculate the system time-invariant reliability. Two cases are investigated to demonstrate the effectiveness of the presented method.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00311-4     

Causes and risk factors for fatal accidents in non-commercial twin engine piston general aviation aircraft

Accidents in twin-engine aircraft carry a higher risk of fatality compared with single engine aircraft and constitute 9% of all general aviation accidents. The different flight profile (higher airspeed, service ceiling, increased fuel load, and aircraft yaw in engine failure) may make comparable studies on single-engine aircraft accident causes less relevant. The objective of this study was to identify the accident causes for non-commercial operations in twin engine aircraft.     

飞行状态下涡扇发动机风扇音频信号合成

为了能以快速、低成本的方式获得飞机起飞过程中,噪声适航审定飞越噪声测量点处涡扇发动机风扇部件的音频信号,对该音频信号的合成方式进行了研究,并提出了一种基于Heidmann风扇噪声预测模型的音频信号合成方法。该方法首先将环境参数、涡扇发动机风扇部件的尺寸参数和性能参数输入Heidmann预测模型得到源噪声数据,根据ANP数据库计算得到航迹数据,接着根据航迹数据对源噪声数据进行修正,得到噪声适航审定飞越噪声测量点处噪声数据。将上述数据输入Adobe Audition软件,分别用加法合成法和减法合成法合成单音噪声和宽频噪声,再在该软件中对噪声进行组合拼接,最后得到飞行状态下风扇部件的音频信号。对合成的音频信号进行播放并使用声学测量仪器进行测量,验证了该方法的正确性和有效性。     

利用航空发动机静态远场噪声数据预测飞行噪声级

装备改进型航空发动机的飞机投入运行前,需对该飞机进行噪声适航再审定。通过发动机静态测试数据预测飞机飞行噪声级,将减少再审定成本。通过“以机代台”试验方法,获得某型航空发动机静态远场噪声数据,将静态测试数据修正到飞行状态,从而预测装配该型航空发动机飞机的飞行噪声级,通过与实际飞行测量结果比较,验证利用静态测试数据预测飞行噪声级的可行性。     

Achievements in Commercial Production of PM Disks and Shafts for Aircraft Engines in Russia

The paper shows stages of development of Ni-base superalloy powder metallurgy in Russia, including modifying of the alloys, with the reference to this new technology, production, testing and flying service of turbine disks in various aircraft engines. Histograms plotted from the results of mechanical property testing are presented. Prospects of application of PM Ni-base superalloys in production of aircraft engines are shown.