Airworthiness Certification Research Articles

A deformation detection method for aircraft skin on uniform pressure by using speckle image correlation technology

The fatigue cracks of aircraft skin which are caused by the pressurization for a civilian airplane during the flight process will bring potential serious safety risks. Therefore, it is necessary to study the deformation mechanism for the aircraft skin on uniform pressure. Traditional fatigue testing machines can only be used for simple tension and compression tests which cannot be applied directly. This paper proposes a deformation detection method by using speckle image correlation technology. Firstly, a fatigue testing machine simulating uniform pressure has been designed. Secondly, a speckle image correlation method by using improved KLT (Kanade-Lucas-Tomasi) algorithm is presented to obtain the coordinates of the coated speckle spots. Finally, static and dynamic experiments were implemented to verify the accuracy and effectiveness of the proposed method. In conclusion, this method can be applied in airworthiness certification to improve the testing efficiency.

Damage tolerance of CFRP airframe bolted joints in bearing, following bolt pull-through failure

The experimental study presented herein, investigated the residual strength of bolted joints on Carbon Fiber Reinforced Polymer (CFRP) airframe structures within the context of structural damage tolerance and airworthiness regulations. The damage scenario assumed, subjected a series of bolted joint CFRP laminate specimens to quasi-static bearing loading, following bolt pull-through failure events of different magnitude. Representative CFRP laminate specimens manufactured from AS7/8552 carbon fiber/epoxy matrix system were artificially damaged under bolt pull-through loading, following the herein proposed modifications to the current pull-through ASTM testing procedure. The specimens were subsequently tested in static bearing loading for examining the specimen residual bearing strength. The residual joint bearing strength was related to the displacement travelled passed the initial failure stage in pull-through mode and was measured up to a maximum of a 13% decrease for the tested samples and the maximum damage imposed. The study explored the safe utilization of bolted joints at higher operating loading levels, within the context of the current airworthiness regulations. The inherent damage arrest features of the joints were highlighted. The study concluded with comments and suggestions on the expansion of the current utilization spectrum of damaged bolted joints from pull-through loading in airframe design, bound by the current airworthiness certification requirements.

Requirements Management Applied in Airworthiness Certification in the Civil Aircraft

The civil aircraft certification is the process, which indicates whether aircraft design complies with airworthiness regulations, or not. In recent years, requirements management has been gradually implemented in civil aircraft design, showing a method, which can implement a series of stakeholder, needs or expectation including airworthiness into specific products through requirements definition, validation and verification. Requirements are hierarchical and structured, however, the lack of technical hierarchy of regulations as provisions results in a poor correlation between regulations and requirements. This paper focuses on the research about the application of requirement based engineering method in the development of civil aircraft, and exploring how to implement the regulations in the whole life cycle of the aircraft development to effectively ensure that the regulations are fully implemented into the product requirements, and fully interacted with the system development process. To a certain extent, avoid the disconnection between the airworthiness regulations and the development process, and reduce the risk that the development of civil aircraft does not meet the airworthiness regulations.

A Novel Semantic Cohesion Approach for Chinese Airworthiness Regulations: Theory and Application

Airworthiness regulation documents are critical, which contain massive safe constraints for system design and airworthiness certification. The textual information of airworthiness regulations is organized and stored in a hierarchical and scattered form due to the unique provision structure. The linguistic form of legal provision brings the problems of incompleteness semantic information and syntactic structure to each legal clause, which limits the application of Natural Language Processing (NLP) technology in the field of airworthiness safety. In this article, a novel theory of semantic cohesion is proposed for Chinese airworthiness regulations, in which four critical elements are contained, including definition, model, theorem and rules. The definition of attributive directed graph model is proposed to achieve the graphical representation of airworthiness regulation texts. Moreover, the graphical issue of regulation texts is proved in accordance with the characteristic of hierarchical provision structure based on graph theory, and the rules of edge structure construction are provided. Based on the theory, a new node content link algorithm is proposed to achieve the tasks of semantic cohesion and structure conversion for Chinese airworthiness regulation texts. According to the hierarchical structure characteristic of regulation texts, the algorithm can convert the provision structure to the general narrative linguistic form by constructing edges with semantic cohesion relation. As a result, provision sentences with complete semantic information and syntactic structure can be generated. The algorithm has been deployed on the current 119 airworthiness regulation texts to verify the validity and feasibility. The experimental results show that the algorithm achieves efficient performance in the tasks of structure conversion and semantic cohesion, and the algorithm performs reliably with an accuracy rate of 100%. The problem of application limitation for NLP technology to Chinese airworthiness regulation texts has been resolved, which promotes the intelligent and automatic development of airworthiness safety.

Design of Image Recognition Algorithm for Critical Flight Parameters in Civil Aircraft Display System

In the current civil aircraft display system design, complex COTS devices such as CPU and GPU have been widely used. While improving product performance, it also greatly increases the difficulty of airworthiness certification. Taking the display system as an example, the data integrity of the critical flight parameters which is displayed on the display unit must reach 1.0E-7 or higher, and the development assurance level of each software and hardware module must reach level B or higher. However, according to industry experience, the data integrity of CPU and GPU can only reach the level of 1.0E-6. Therefore, for the critical flight parameters in the display system, it must be monitored to cover the entire data path from data processing to image generation to prove the data validity. Aiming at the numeric critical flight parameters of civil aircraft display system, this paper proposes a numeric image recognition technology realized by FPGA image processing function, which can be used to monitor the integrity of numeric critical flight parameters, and this technology has been performed and verified in real display unit.

Preliminary Design of a Model-Free Synthetic Sensor for Aerodynamic Angle Estimation for Commercial Aviation.

Heterogeneity of the small aircraft category (e.g., small air transport (SAT), urban air mobility (UAM), unmanned aircraft system (UAS)), modern avionic solution (e.g., fly-by-wire (FBW)) and reduced aircraft (A/C) size require more compact, integrated, digital and modular air data system (ADS) able to measure data from the external environment. The MIDAS project, funded in the frame of the Clean Sky 2 program, aims to satisfy those recent requirements with an ADS certified for commercial applications. The main pillar lays on a smart fusion between COTS solutions and analytical sensors (patented technology) for the identification of the aerodynamic angles. The identification involves both flight dynamic relationships and data-driven state observer(s) based on neural techniques, which are deterministic once the training is completed. As this project will bring analytical sensors on board of civil aircraft as part of a redundant system for the very first time, design activities documented in this work have a particular focus on airworthiness certification aspects. At this maturity level, simulated data are used, real flight test data will be used in the next stages. Data collection is described both for the training and test aspects. Training maneuvers are defined aiming to excite all dynamic modes, whereas test maneuvers are collected aiming to validate results independently from the training set and all autopilot configurations. Results demonstrate that an alternate solution is possible enabling significant savings in terms of computational effort and lines of codes but they show, at the same time, that a better training strategy may be beneficial to cope with the new neural network architecture.

Overview regarding the certification of a new military jet aircraft for school and training

The requirements for designing a new Romanian school and training military jet, IAR 99 NG, are in line with the EMAR - European Military Airworthiness Requirement. The Approval Regulation for the new school and training military jet is EMACC - European Military Airworthiness Certification Criteria. In addition to the basic regulation, the main categories of norms used for designing, manufacturing and testing are as follows: AIR, MIL, NA, EN and SR EN etc. For each system used on the new school and training military jet, Standard Defense 00-970 and NATO STANAG regulates the requirement to perform tests on a functional model. In order to be tested, each modeled system, must accurately reproduce the original system.

Progress in the airworthiness technology of civil aero-engine

According to the airworthiness technology of civil aero-engine, the historical evolution of airworthiness regulation, FAR 33, is investigated. And the general rules are obtained which include developing form, influencing factors of development, and changing trend. Furthermore, the analysis of airworthiness verification technology will be presented in the four aspects which are use, working environment, structure, and system. Plus, the critical points of airworthiness certification and management are discussed. Based on the analysis above, the opportunity and challenge the airworthiness certification work face in the next period are finally prospected, to provide a reference for the related research in the aviation industry.

Integrated Airworthiness Certification Criteria and Security Risk Assessment for UAVs

The proportion of software in UAVs has increased rapidly in recent years. However, it is becoming increasingly difficult to secure the avionic software against security threats. There are no airworthiness certification criteria for the security as well as the safety of UAVs. Therefore, it will be necessary to study on the airworthiness certification criteria and methodology for the safety and security of UAVs, considering the recent trend of the increase in the use of UAVs. The integrated airworthiness certification criteria for safety and security in avionic software to save time and cost were most recently proposed. This paper introduces the comparison between CC, DO-178C, and airworthiness security activities. It also presents the quantitative risk assessment method that is capable of analyzing vulnerabilities and assesses risks quantitatively using the case of security threats to the avionic software of UAVs. It derives the security objectives and requirements for UAVs’ avionic software based on the result of the security risk assessment. Finally, this paper proves the effectiveness of the risk assessment methods by applying them to real case of UAVs.

Korean Utility Helicopter KUH-1 Icing Certification Program

<div class="section abstract"><div class="htmlview paragraph">The KUH-1 Surion is a twin-engine utility helicopter designed and developed jointly by Korea Aerospace Industries (KAI) and Airbus Helicopters primarily for the Republic of Korea Army (ROKA). Following customer requirements, KAI launched a program aimed at the military qualification of the KUH-1 for flight in icing conditions following tailored airworthiness certification criteria based on 14 CFR Part 29 and DEF STAN 00-970. The Netherlands Aerospace Centre (NLR) became involved in the program on the eve of the first icing flight test campaign performed in the winter of 2015/2016. NLR has supported all subsequent test activities and the finding of compliance in close collaboration with KAI and certain suppliers. The test activities performed include 1) component-level development and qualification icing wind tunnel testing at Cox & Co in Long Island, NY, 2) icing qualification testing of the engine air intake ice protection system at Rail Tec Arsenal (RTA) in Vienna, Austria, 3) artificial icing flight testing using the US Army Helicopter Icing Spray System (HISS), and 4) natural icing flight testing of the complete aircraft in the state of Michigan, USA. Following the extensive test activities, the KUH-1 was granted icing qualification by the Korean military airworthiness authorities in June of 2018. This paper provides an overview of the KUH-1 icing certification program, followed by a more detailed accounting of the most recent icing wind tunnel and flight test activities as outlined above, and a description of the ice protection system design for the engine air intake, the upper wire cutter and the main rotor system.</div></div>

Research on the measurement of hexafluoropropane based on a mid-infrared quantum cascade laser

Hexafluoropropane (HFC-236fa) is a kind of Halon substitute, which is expected to be applied in the aircraft fire suppression system. The spatial distribution of fire extinguishing agent in protected area is an important assessment parameter in the airworthiness certification of aircraft fire protection systems. In this research, a concentration measurement system of hexafluoropropane has been developed using a quantum cascade laser at ∼8280 nm. The measurement of hexafluoropropane based on mid-infrared absorption spectrum was reported for the first time. In experiment, the system showed good performance in the measurement range of 0–15% with a full scale error of 0.87%FS, while the fast response time within 250 ms was obtained. Moreover, this system can be also used in the sensitive detection of hexafluoropropane leakage and the monitoring of greenhouse gas hydrofluorocarbons. The detection limit of 100 part per million (ppm) can be obtained with an 85-cm-long gas cell.

Fast-response concentration measurement of bromotrifluoromethane using a quantum cascade laser (QCL) at 8280 μm

In this study, a measurement system for a gaseous fire extinguisher bromotrifluoromethane (Halon 1301) was developed, using a quantum cascade laser (QCL) at ~8.280 μm. The performance parameters of this system were also analyzed. Much higher sensitivity and faster response time were achieved compared to non-dispersive infrared (NDIR) sensors and differential-pressure method. A response time of 90 ms from 0% to the targeted concentration 6% was obtained. The detection limit of 500 ppm was obtained with a short optical path length of 2.8 mm. In conclusion, the proposed system can be applied in the airworthiness certification test of an aircraft fire suppression system.

Static testing for composite wing of a two-seater seaplane

The paper studied the strength and deformation characteristics of a composite wing of a two-seater seaplane to get the certificate of airworthiness which static testing is indispensable. The primary wing structure component includes upper and lower skins, leading edge, trailing edge, a root rib and main spar. The main purpose of static testing is to examine the bending strength of the wing. The testing results show good agreement with the FE analysis results, and the bending strength of wing is strong enough to support the limit loads (the maximum loads to the expected in service) without detrimental and permanent deformation, and without failure for at least 3s under the ultimate loads (limit loads multiplied by prescribed factors of safety), which meets the requirement of ASTM F2245-16c (Standard Specification for Design and Performance of a Light Sport Airplane).

Probabilistic Safety Assessment for UAS Separation Assurance and Collision Avoidance Systems

The airworthiness certification of aerospace cyber-physical systems traditionally relies on the probabilistic safety assessment as a standard engineering methodology to quantify the potential risks associated with faults in system components. This paper presents and discusses the probabilistic safety assessment of detect and avoid (DAA) systems relying on multiple cooperative and non-cooperative tracking technologies to identify the risk of collision of unmanned aircraft systems (UAS) with other flight vehicles. In particular, fault tree analysis (FTA) is utilized to measure the overall system unavailability for each basic component failure. Considering the inter-dependencies of navigation and surveillance systems, the common cause failure (CCF)-beta model is applied to calculate the system risk associated with common failures. Additionally, an importance analysis is conducted to quantify the safety measures and identify the most significant component failures. Results indicate that the failure in traffic detection by cooperative surveillance systems contribute more to the overall DAA system functionality and that the probability of failure for ownship locatability in cooperative surveillance is greater than its traffic detection function. Although all the sensors individually yield 99.9% operational availability, the implementation of adequate multi-sensor DAA system relying on both cooperative and non-cooperative technologies is shown to be necessary to achieve the desired levels of safety in all possible encounters. These results strongly support the adoption of a unified analytical framework for cooperative/non-cooperative UAS DAA and elicits an evolution of the current certification framework to properly account for artificial intelligence and machine-learning based systems.

Robustness Analysis of Flight Controllers for Fixed-Wing Unmanned Aircraft Systems Using Integral Quadratic Constraints

A robust analysis framework for mathematical validation of flight control systems is presented. The framework is specifically developed for the complete uncertainty characterization, quantification, and analysis of small fixed-wing unmanned aircraft systems (UAS). The analytical approach presented within is based on integral quadratic constraint (IQC) analysis and uses linear fractional transformations on uncertainties to represent system models. While IQC analysis has a sound theoretical foundation, there remains a lack of literature on applying IQCs to complex engineering systems and evaluating their effectiveness with physical data. One difficulty lies in appropriately characterizing and quantifying the uncertainties such that the resulting uncertain model is representative of the physical system while forming a computationally tractable problem that is not overly conservative. This paper addresses these challenges by applying IQC analysis tools to analyze the robustness of a UAS flight control system. Uncertainties are characterized and quantified based on mathematical models and flight test data obtained in-house for a small commercial off-the-shelf platform with a custom autopilot. Furthermore, an established gradient-based minimization routine is implemented with IQC analysis to demonstrate how IQC analysis can guide the control design process. This approach also reveals the controlled system’s sensitivities to uncertainties, thereby assisting the designer in determining how much uncertainty allowance ought to exist in certain aspects of the UAS. Finally, these methods are tested in physical flight to showcase the effectiveness of IQC analysis and assess the conservativeness of the approach. The proposed framework is also transferable to other fixed-wing UAS platforms, effectively taking IQC analysis beyond academic examples to practical application in UAS system design, control design, and airworthiness certification.

Accuracy analysis of a single-fault Markov model for FADEC system

Time-limited dispatching (TLD) analysis of the full authority digital engine control (FADEC) systems is an important part of the aircraft system safety analysis and a necessary task for the certification of commercial aircraft and aeroengines. In the time limited dispatch guidance document ARP5107B, a single-fault Markov model (MM) approach is proposed for TLD analysis. However, ARP5107B also requires that the loss of thrust control (LOTC) rate error calculated by applying the single-fault MM must be less than 5% when performing airworthiness certification. Firstly, the sources of accuracy errors in three kinds of MM are analyzed and specified through a case study of the general FADEC system, and secondly a two-fault MM considering maintenance policy is established through analyzing and calculating the expected repair time when two related faults happen. Finally, a specific FADEC system is given to study on the influence factors of accuracy error in the single-fault MM, and the results show that the accuracy error of the single-fault MM decreases with the increase of short or long prescribed dispatch time, and the range values of short time (ST) and long time (LT) are determined to satisfy the requirement of accuracy error within 5%.

Taxiing stability verification and airworthiness certification for amphibious aircraft

Taxiing stability verification and airworthiness certification for amphibious aircraft

Evaluation of bird strike-induced damages of helicopter composite fuel tank assembly based on fluid-structure interaction analysis

We numerically investigated the structural behaviors and damage of a bird strike on a composite fuel tank assembly of a commercial KUH-1 Surion utility helicopter based on a fluid-structure interaction analysis. A coupled Eulerian–Lagrangian method and a smoothed particle hydrodynamic method were applied to consider the sloshing of fuel and replicate the impact behaviors of a bird strike, respectively. In addition, the Hashin failure criteria considering four composite damage modes was applied in the simulation. We found that not only the increase in the amount of fuel but also the curved geometry had a negative effect on the structural safety of the composite fuel tank during the impact. These findings will be used as reference data and guidelines for bird strike tests and airworthiness certification in the future.

A model‐based flight qualities evaluation approach for civil aircraft

SummaryEvaluation of flight qualities plays an important role in the design of a civil aircraft. An appropriate level of flight qualities will be the key to achieve the airworthiness certification. With the objective to provide an overall view of flight qualities evaluation for a civil aircraft, a model‐based approach is proposed. Some terms related to flight qualities are defined formally, and the model‐based flight qualities evaluation approach under different situations is formed and proposed. Two working conditions of actuators are considered in the evaluation of flight qualities. When no actuator fails, linearization is adopted to build a linear flight dynamics model for analyzing the main parameter of flight qualities. When some actuators fail, a new off‐line approach for handling qualities evaluation, which employs a controller that generates appropriate commands for healthy actuators, is proposed. The design of the controller is following the idea of classical predictive control technique, and a recurrent linear quadratic programming problem is formulated to find the maximum remaining maneuverability while not avoiding any constraints. Taking the rotational maneuver as a study example, a test‐bed for handling qualities evaluation is built. The numerical simulation results show the feasibility of proposed evaluation approach.

Review of Formal Agile Methods as Cost-Effective Airworthiness Certification Processes

Review of Formal Agile Methods as Cost-Effective Airworthiness Certification Processes