Flight Critical Systems Research Articles

Least Risk Bomb Location Explosives Identification, Detection and Mitigation

This paper investigates the still evolving strategic trajectories and the context adopted for the procedures for inducting a Least Risk Bomb Location (LRBL) that began with discretionary participation by various aircraft manufacturers approximately in the year 1972, where the use of a specific procedure has been designed to decrease the effects of an explosion significantly in the aircraft’s passenger cabins of large commercial airplanes. Additionally, the International Civil Aviation Organization (ICAO) has provided the information on the location of the LRBL and guidance to various operators (National/International)on the procedures to use when a suspected threat item is found on-board an airplane. The designation of LRBL for aero planes is intended to be used solely for the transport of cargo, where an aero plane must include a designated location where a bomb or other explosive device could be designated to protect integrity of the structure and flight-critical systems from damage in the case of detonation occurs.

Preliminary study towards the definition of a PHM framework for the hydraulic system of a fly-by-wire helicopter

On-board hydraulic systems are tasked to provide a number of critical functions to ensure the in-flight operability of rotary-wings vehicles; the hydraulic plant is required to supply power to the flight control actuators and utilities, as well as condition the hydraulic fluid, under a wide range of possible in-service conditions. Being a flight-critical system, the definition of a Prognostics and Health Management framework would provide significant advantages to the users, such as better risk mitigation, improved availability and a reduction in the occurrences of unpredicted failures which still represent one of the more known downsides of helicopters. A preliminary analysis on the effects of the inception and progression of several degradation types is the first step towards assessing if such PHM system is feasible, and which failure modes are more likely to be observed. Moreover, since several key components are frequently provided by different suppliers to the airframer, this preliminary analysis would allow to better assess if an Integrated Vehicle Health Management approach, integrating signals coming from different components, could be beneficial. To pursue this study, a complete model of the hydraulic system for a fly-by-wire helicopter has been prepared. Then, an in-depth simulation campaign was pursued with the aim of studying the interactions between different failure modes, the effects that the propagating degradations have on the system performances and which signals can be used to define a robust set of features. The paper introduces the case-study under analysis, a general configuration for fly-by-wire helicopters, presenting the most prominent peculiarities of the system and the effect of such peculiarities on the definition of health monitoring schemes. The model is then used to describe the behavior of the system under nominal and degraded conditions is introduced. Between the possible failure modes, the interaction between wear in several mechanical components and the occlusion of the hydraulic lines filters was chosen as the subject of this study; motivations are provided and the degradation model described in detail. Hence, results of a wide-ranging simulation campaign are presented, where the time-domain response of the system is used to guide in the definition of a proper set of features able to characterize the selected fault cases. Selected features are presented, chosen according to significant metrics such as correlation with the simulated degradations, signal-to-noise ratio and accuracy. Two different approaches with a varying degree of integration between system signals are proposed and compared. Prognostics is then pursued through well-known particle filter algorithms. The analysis provides promising results on the capability of successfully detecting, isolating and identifying the selected fault mode; laying the foundations for further and more comprehensive studies on the subject.

System Reliability Estimation of Divert Attitude Control System of a Launch Vehicle using Bayesian Networks

Divert attitude and control system (DACS) is a one-shot system and provides attitude correction and translation of the Launch vehicle. DACS consists of many flight critical sub systems which are arranged in a series configuration. The traditional Reliability block diagram and Fault tree diagram methods are unsuitable for reliability modelling, when considering uncertainty among the components and system. Bayesian network is the natural choice to model dependencies among the components and system. DACS being one shot system, it is very expensive and time consuming to test more number of systems during the design and development. Hence the data is drawn from component level, subsystem level and expert opinion is used for reliability estimation. In this paper, Bayesian network modelling of DAC system was carried out for estimating the reliability using multi-level data. An algorithm is developed for computation of Conditional probabilities in Bayesian network. Posterior probability distribution of components is calculated using Markov Chain Monte Carlo (MCMC) simulations and results are compared with Junction tree based exact inference algorithm. MATLAB code is developed to estimate the reliability of DAC system.

Penetration Mechanics of GLARE™ Fiber-Metal Laminates upon Collision with Micrometeoroids

The spacecraft designed for long-duration service are susceptible to hypervelocity impacts of micrometeoroids and orbiting space debris. Such impacts on spacecraft structures can cause spacecraft failure and loss of life. In order to adequately protect the spacecraft bulkhead and flight critical systems, many high-strength composite materials have been developed for debris bumper. GLAss fiber REinforced aluminum is one of the high-performance composites. The review of articles, however, yielded no single study, which has been dedicated to interrogate the damage mechanics of GLAss fiber REinforced aluminum upon collision with micrometeoroids. This study, therefore, aimed at the numerical investigation of penetration phenomena of thick GLAss fiber REinforced aluminum 5-6/5-0.4 laminates upon hypervelocity impact of a projectile. The numerical study employed a predictive model that merged the smoothed particle hydrodynamics and the finite element methods. The model could predict the colossal damage modes of GLAss fiber REinforced aluminum. As seen, the normal impact of a 2 mm diameter spherical 2024-T3 aluminum projectile on GLAss fiber REinforced aluminum, at a relative velocity of 7.11 km/s, resulted into membrane stretching and fiber failure of the glass fiber reinforced epoxy composite laminates. By contrast, the aluminum layers experienced an enormous strain-rate and consequently, suffered thinning, fracture and large mass erosion. The perpetual release waves fragmented the projectile and dispersed the projectile mass prior to the further penetration of GLAss fiber REinforced aluminum. To verify the accuracy of the numerical model, experiments had been conducted by using a two-stage light-gas gun. The experiments generated damage modes of GLAss fiber REinforced aluminum in good correspondence to that of the predictive model. Yet, disparity between the estimations of experiments and simulations had been apparent, which is anticipated due to the phase change of material had not been accounted for in the analysis.

The challenge of advanced model-based FDIR for real-world flight-critical applications

This paper aims at providing a brief perspective of advanced model-based Fault Detection, Identification and Recovery (FDIR) for aerospace and flight-critical systems. A number of practical key factors for designing credible technological options are emphasized. Such considerations are decisive for the survivability of the design during ground/flight Validation & Verification (V&V) activities. The views reported in this paper are based on lessons learnt and results achieved through actions undertaken with Airbus during the last decade. As an illustrative example, a model-based fault monitoring technique is presented which has reached level 5 on Technological Readiness Level scale under V&V investigations at Airbus.

Analysis of electrical discontinuity problem in MLB using Ishikawa model

Purpose The purpose of this study/paper is regarding analysis of electrical discontinuity in penultimate layer of a few batches of Multilayer Boards (MLB) fabricated and supplied by a vendor. The ever-increasing demand of miniaturization in launch vehicle and spacecraft electronics systems has led to the usage of multilayer printed circuit boards (PCBs) for realizing high-performance electronics circuitry. Multilayer boards (MLBs) fabricated by qualified agencies based on the customer requirement are being used in the critical launch vehicle/spacecraft systems after evaluating the preliminary test results supplied by the vendor. However, a few batches of MLBs fabricated and supplied by a particular vendor (“A”) showed a discontinuity problem in a few PCB tracks connected by soldering pads. As these MLBs are part of Flight critical systems of both launch vehicle and spacecraft, a malfunction in the board may lead to fatal errors during fight or on-orbit, thereby jeopardizing the mission. Design/methodology/approach A systematic approach was followed to have a thorough understanding of the problem, and major tests such as inspection, continuity measurement, microsection of the plated through hole (PTH) and Scanning Electron Microscopy–Energy Dispersive X-ray Analysis tests were conducted on identified test boards based on Ishikawa model. Emphasis was given for horizontal microsection, as it has got a clear edge in detecting defects at any point of PTH barrel to inner-layer copper interface. Findings Systematic testing and evaluation on specimen revealed the presence of unwanted material at the bonding area of inner-layer copper and PTH copper due to inadequate fabrication process. The un-cleaned epoxy materials present at the bonding area creates a weak bond between barrel and inner-layer copper. Electrical strength of the MLB is the strength of this link. This weaker interconnection leads to electrical discontinuity of inner-layer tracks. Originality/value MLBs are part of Flight critical systems of both Launch Vehicle and Spacecraft; a malfunction in the board may lead to fatal errors during fight or on-orbit, thereby jeopardizing the mission. Case study of an original failure observed in MLBs helped to achieve normal functioning of systems and avoided failures at later stage of mission.

Physics‐based RF/microwave characterization of wave interactions within electrical connectors with partial insertion faults

AbstractElectrical failures in avionics systems may result from connector faults. If fault precursors are not detected in advance, they may lead to hard failures such as open and short circuits that could ultimately result in fire or loss of flight critical systems. Therefore, It is crucial to detect, locate, and characterize fault precursors for timely preventive maintenance and mitigation before hard failures occur. In this paper, a physics‐based connector model consisting of multiple coaxial line sections with different characteristic impedances and lengths is proposed. Method of Moments (MoM) analyses were performed using commercial electromagnetic simulation software, FEKO, for transverse electric and magnetic (TEM) wave propagation through a connector. The physical parameters of the connector were optimized to match the measured S parameters for multiple insertion depths. The proposed models represent the connector for multiple insertion depths by varying only two length parameters at a time while other parameters are fixed. Insertion depth‐dependent resonant frequency shifts observed during measurement are also captured by the model over the full range of fully inserted to barely touching contacts. Hence, the models provide accurate representations of the connector and properly detect precursors to partial insertion faults.

Intelligent Flight Control Systems Evaluation for Loss-of-Control Recovery and Prevention

Recent developments in the field of loss-of-control recovery and prevention included improved pilot training, cockpit automation, and fault-tolerant control. The Flight Mechanics Action Group on Fault-Tolerant Control of the Group for Aeronautical Research and Technology in Europe demonstrated the advantages of fault-tolerant “intelligent,” flight control systems. The research enabled the improvement of the technology readiness level of these systems by evaluating one of them in realistic operational scenarios. The handling qualities results of a piloted flight simulator assessment with a damaged aircraft model showed that an online physical model identification approach contributed to improved pilot performance following potentially catastrophic structural and flight critical system failures. After the failures and subsequent control reconfiguration by the intelligent flight control system, airline and engineering test pilots experienced no difficulties in conducting a safe approach and landing.

Integrated thermoelectric model for on-board aircraft generators

Abstract: Electronic systems are becoming the predominant method for flight critical systems and have substituted their pneumatic or hydraulic counterparts, increasing the need for constant and uninterrupted supply of power. One of the main limitations is overheating in generators due to an increased demand of current. Overheat in the generator windings can lead to insulation degradation and hence to catastrophic failure. Therefore, understanding and monitoring heat flow through the generator is of utmost importance. Previous studies have viewed the electrical and thermal circuits as separate arrangements with little interaction between the two. This paper attempts to provide a systemic thermo-electric view of the generator and offer a method for interfacing the thermal and electrical circuits by the use of loss calculation. The long term goal of this project is to provide a means for model based health assessment and intelligent power management for on-board aircraft generator systems, while having limited information on the system itself.

Simulation of Characteristics of Debris Cloud Produced by Hypervelocity Impact

All spacecraft in low orbit are subject to hypervelocity impacts by meteoroids and space debris. These impacts can damage spacecraft flight-critical systems, which can in turn lead to catastrophic failure of the spacecraft. The numerical simulations of characteristics of debris cloud produced by an aluminum sphere projectile hypervelocity impact on different material bumpers at normal incidence have been carried out by using the SPH (smoothed particle hydrodynamics) technique. The effects of impact velocity, the ratio t/d of the bumper thickness to the projectile diameter and the bumper materials on the debris cloud characteristics are presented.

An Overview of the V & amp;V of Flight-Critical Systems Effort at NASA

As the US is getting ready for the Next Generation (NextGen) of Air Traffic System, there is a growing concern that the current techniques for verification and validation will not be adequate for the changes to come. The JPDO (in charge of implementing NextGen) has given NASA a mandate to address the problem and it resulted in the formulation of the V&V of Flight-Critical Systems effort. This research effort is divided into four themes: argument-based safety assurance, distributed systems, authority and autonomy, and, software intensive systems. This paper presents an overview of the technologies that will address the problem.

KUH 임무탑재시스템의 안전성설계 및 검증

안전성 요구수준이 서로 다른 비행필수 데이터(Flight Critical Data)와 임무필수 데이터(Mission Critical Data)의 시현을 처리하기 위해 별도의 독립된 계기를 사용하지 않고 Glass Cockpit 설계를 적용하여 데이터를 통합처리하였다. 본 논문에서는 독립적으로 설계 진행되어온 비행조종계통과 임무탑재시스템의 통합설계를 위해 설계변경을 최소화하면서 비행조종계통에서 요구되는 비행필수 데이터처리의 안전성 요구수준을 만족시키는 최적화 설계를 제안하였다. 비행필수 데이터의 시현을 처리하기 위해 KUH 임무탑재시스템의 핵심구성품인 임무컴퓨터(Mission Computer)의 하드웨어 및 소프트웨어 설계변경을 최소화하였다. 임무탑재시스템의 안전성 요구도(Safety Requirement)를 검증하기 위한 시험절차를 개발하여 임무탑재시스템 통합시험장비(SIL)를 이용한 시험 수행 결과 안전성 요구도가 만족됨을 확인하였다. Integrated data processing for display of flight critical data and mission critical data was conducted without additional display instruments using glass cockpit design. Based on a pre-designed flight critical system and a mission critical system, this paper shows an optimal design of subsystem integration. The design satisfies safety requirements of flight control systems(FCS) and requires minimized modification of pre-designed systems. By conducting integration test using System Integration laboratory(SIL), it is confirmed that the introduced design approach meets the safety requirements of the MEP system.

Probability of Loss Assessment of Critical $k$-Out-of-$n$:G Systems Having a Mission Abort Policy

The survival of an aircraft is dependent on continuous operation of its flight critical systems until it has safely landed. Such a system may utilize a mission abort policy, requiring termination of typical mission operations, and entering a recovery phase in the event of certain failures. If, subsequent to such a mission abort fault, the system is able to safely complete the recovery phase, it will have survived, but may have failed to complete its mission objectives. This type of system is of interest when 1) the system's survival is dependent on its unattended operational capability; 2) there exist circumstances under which system survival has a greater priority than completing a mission of defined length; or 3) a mission abort policy can be established which results in entering a recovery phase requiring less time than completing the mission. Computing the probability of mission survival for systems using a mission abort policy is not a classical reliability problem, generally defined as the probability of performing its intended mission for a specified period of time, because the assessment does not, in general, involve a mission of a specific period of time. The period of time of interest will be either the specified mission time, or the sum of the time prior to a mission abort plus the time required to complete a recovery phase. This paper addresses determining the probability of survival for redundant systems utilizing a mission abort policy. Systems having both perfect, and imperfect fault coverage are addressed; and numerical, and exact algebraic results are provided for i.i.d. <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> -out-of- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> :G systems.

Investigation of the Electromagnetic Interference Threat Posed by a Wireless Network Inside a Passenger Aircraft

Recent years have witnessed an incisive push to allow the use of wireless networks inside passenger aircraft. Research was recently conducted to investigate the internal electromagnetic (EM) environment excited by a wireless network inside a passenger aircraft to provide quantification of the ensuing EM interference threat. An airbus A319 EM model was developed and validated using experimental data and analytical techniques. The validated model was applied to the investigation of an 800 MHz cellular network. The peak electric field strength inside each of the A319 EM models examined was much less than the most severe RTCA/DO-160D radiated susceptibility test levels. The current coupled to a cable running along the length of the fuselage was much less than the minimum operating parameters of an extremely sensitive avionic system (e.g., strain sensor). The results obtained help to quantify and reinforce the conclusion of the major research efforts that the likelihood of interference with flight critical systems is low. The model presented herein can be easily adapted to study EM propagation for various types of wireless network and aircraft configurations, and the modeling approach employed could be of potential use in modeling other large, complex structures.

Prognostics and Health Management as Design Variable in Air-Vehicle Conceptual Design

Flight critical systems in air vehicles achieve required reliability through different redundancy design techniques including physical system redundancy. Prognostics and health management technology provides the opportunity to eliminate some of the physical redundancy (and associated weight) through implementation of accurate remaining useful life algorithms. Consideration of this subsystem design approach up front during the conceptual design process rather than downstream during the detailed design phase of the air vehicle system can produce a more optimal air-vehicle configuration with regard to reliability and weight. Results are presented for an unmanned air-vehicle design optimization, which included remaining useful life algorithm confidence, control surface actuator redundancy, and control surface configuration as optimization variables. Optimization constraints included landing dispersion, mission reliability, and mission availability. Reductions in air-vehicle weight were achieved with reasonable algorithm confidence requirements.

Characterizing secondary debris impact ejecta

All spacecraft in low earth orbit are subject to high-speed impacts by meteoroids and orbital debris particles. These impacts can damage flight-critical systems, which can in turn lead to catastrophic failure of the spacecraft. In addition to threatening the operation of the spacecraft itself, on-orbit impacts also generate a significant amount of damaging ricochet ejecta particles. These high-speed particles can destroy critical external spacecraft subsystems, which also poses a threat to the spacecraft and its inhabitants. Since the majority of on-orbit debris impacts are expected to occur at oblique angles, the characterization of ricochet debris created in an orbital debris particle impact is an issue that must be addressed. This paper presents the results of a study performed to develop an empirical model that characterizes the secondary ejecta created by a high speed impact on a typical aerospace structural surface. Specifically, the model predicts the spread and trajectory of ricochet debris particles created in a hypervelocity impact as well as the size an velocity of the most damage particle in the ricochet debris cloud. Results obtained using the model are compared with experimental results and predictions obtained in a previous study.

Neural Network-Based Virtual Sensors In Flight Control Systems

This paper presents a study aiming at reducing the cost of hardware replication in flight-critical systems, in particular for what concerns the Flight Control System (FCS) sensors. Compliance with the safety requirements is a significant driver in the definition of the total costs of a FCS and the current approach is generally based on the definition of a proper level of hardware redundancy, impacting on both the affordability and complexity of the system. An alternative approach, based on the adoption of soft computing techniques to implement an analytical redundancy, is presented and some results are shown. The objective of the study concerns in particular the possibility of generating additional and synthetic signal sources to be used to validate the physical ones.

Protecting spacecraft against orbital debris impact damage using composite materials

All earth-orbiting spacecrafts are susceptible to impacts by meteoroids and pieces of orbital debris. These impacts occur at extremely high speeds and can damage flight-critical systems, which can in turn lead to catastrophic spacecraft failure. With the advent of many new high-strength composite materials and their proliferation in aircraft applications, it is necessary to evaluate their potential for use in long-duration space and aerospace structural systems. This paper presents the results of several experimental investigations in which several different composite materials were tested for their ability to prevent the perforation of the inner walls in multi-wall systems subjected to hypervelocity projectile impact. Damage to multi-wall systems that employ composite materials is compared to damage in traditional all-aluminum multi-wall structures of similar geometry and weight under similar impact conditions. The advantages and disadvantages of using composite materials in perforation-resistant multi-wall structures are presented and discussed. The analyses performed show that the effectiveness of multi-wall systems with composite materials varies significantly depending upon the location within the multi-wall system of the composite materials. Based on the results obtained, it appears that composite materials are most effective when used as the middle wall of a triple-wall system.

The realism of FAA reliability-safety requirements and alternatives

As avionic systems become more complex, realistic qualification requirements for the flight-critical systems becomes more important, but more difficult to define. Requirements developed to establish acceptable levels of performance must be verifiable if they are to have any meaning. This article shows that both the current FAA requirements of flight-critical systems and the FAA recommended methods for probabilistic assessment are flawed, and result in required safety assessments which are misleading. Alternatives are then explored.

Monitoring Functional Integrity in Fault Tolerant Aircraft Control Computers for Critical Applications

Verifying integrity of control computers in adverse operating environments is a key issue in the development, certification, and operation of critical control systems. For example, future commercial aircraft will necessitate flight-critical systems with high reliability requirements for stability augmentation, flutter suppression, and guidance and control. This paper considers the problem of applying distributed detection techniques and decision fusion to monitoring the integrity of fault tolerant redundant control computers. A monitoring strategy is presented and demonstrated from glideslope engaged until flare using a detailed simulation of a quad-redundant longitudinal control system for the B737 Autoland. The performance of the distributed monitoring system is assessed.