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    What Matters in the Effectiveness of Airborne Collision Avoidance Systems? Monte Carlo Simulation of Uncertainties for TCAS II and ACAS Xa
    (MDPI, 2023) Stroeve, S.H.
    TCAS II is a rule-based airborne collision avoidance system (ACAS) that is used in current commercial air transport operations, and ACAS Xa is a new optimization-based system. Operational validation studies have mainly used deterministic simulations of ACAS performance using various sets of encounters. Recently a new approach was developed, which employs Monte Carlo (MC) simulation of agent-based models to evaluate the impact of sensor errors and pilot response variability. This paper contrasts the results of both approaches in a comparison of TCAS II and ACAS Xa for various types of synthetic encounters. It was found that conventional estimates of near mid-air collision (NMAC) probabilities are often lower than the estimates achieved using MC simulation, and that the biases in the P(NMAC) estimates are consistently larger for ACAS Xa than for TCAS II. Contributions to unresolved risk are largest for pilot performance, then for encounter types, and finally for sensor errors. The contribution of non-responding pilots is much larger than the differences between TCAS II and ACAS Xa. It is concluded that the agent-based MC simulation overcomes the limitations in traditional evaluation of altimetry errors and pilot response, providing an independent means to effectively analyze the robustness of ACASs.
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    Numerical simulation of inductive heating in thermoplastic unidirectional cross-ply laminates
    (Frontiers, 2023) Wit, A.J. de ; Hoorn, N. van ; Straathof, L.S. ; Vankan, W.J.
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    Performance Based Training : White Paper for RNLAF
    (Netherlands Aerospace Centre NLR, 2021) Nabben, A.C. ; Benthem, G.J. van ; Pal, J. van der ; Eaglestone, J.
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    New Generation of Counter UAS Systems to Defeat of Low Slow and Small (LSS) Air Threats
    (NATO, 2021) Dominicus, J.W.
    Detecting, classifying, identifying, tracking and defeating low, slow and small air threats presents a major challenge for existing sensor and effector systems. So-called first generation C-UAS systems often rely on detecting the datalink from the controller to the drone which provides limited capability against current threats. However, this means of detecting drones is a challenge when operators manipulate standard datalinks and will not work at all against current and future autonomous drones. Other current methods of detecting and neutralising drones include for example combining radar with optical sensors. These systems are not always reliable, can generate large numbers of false alerts and are often manpower intensive to operate. The NATO SCI-301 Research Task Group (RTG) has been working on specifying what second generation C-UAS systems should entail. The paper will outline the findings of this RTG over the past three years.
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    Multi-domain contactless NDI approach: Data fusion of structural light scanning with thermography and shearography
    (NDT.net, 2023) Jansen, H.P. ; Platenkamp, D.J. ; Bosch, A.F.
    The proportion of composite materials (such as CFRP) compared to the metal used on modern aircrafts is rising, imposing different kind of failure modes. Since the composite structures are known to be sensitive to impact loading, there is need for means to assess the sub-surface damage in the structure rapidly. Royal Netherlands Aerospace Centre NLR has an extensive track record on contactless non-destructive inspection (NDI) methods based on optical sensors, such as 3D surface scanning, lock-in thermography and laser shearography. The combination of these methods (multi-domain inspection) enables us to assess the structural integrity of an aircraft outer surface in a short time, reducing inspection costs and the “down time” of the aircraft. Recently, NLR is working towards a 3D oriented mesh environment of an object, enhanced with NDI data, providing sub-surface damage information . The combination of the different NDI methods makes it easier to identify and classify different defect types. To demonstrate this procedure a small radome which suffered impact damage after an hail storm is used. The impact damage resulted in dents on the surface which can be detected using 3d Structural light scanning, however the internal structure can not be assed using this technique. Using lock-in thermography damage inside of the skin can be detected, but no skin-to-core disbonds can be detected using single sided inspection. By using shearography it is possible to detect disbonds between the glass fibre skin and the nomex honeycomb core. Using the combination of the aforementioned techniques, it is possible to assess the overall health of the radome. Additionally , in order to demonstrate this techniques on a larger part results from a 747-400 right hand inboard aft flap is also shown . All techniques are non-contact also allowing for a great deal of automatization during inspection.