An Airbus A340 aircraft flew over Northern Australia with the In‐Flight Lightning Damage Assessment System (ILDAS) installed onboard. A long‐duration gamma ray emission was detected. The most intense emission was observed at 12 km altitude and lasted for 20 s. Its intensity was 20 times the background counts, and it was abruptly terminated by a distant lightning flash. In this work we reconstruct the aircraft path and event timeline. The glow‐terminating flash triggered a discharge from the aircraft wing that was recorded by a video camera operating onboard. Another count rate increase was observed 6 min later and lasted for 30 s. The lightning activity as reported by ground networks in this region was analyzed. The measured spectra characteristics of the emission were estimated.

We report a 511‐keV photon flux enhancement that was observed inside a thundercloud and is a result of positron annihilation. The observation was made with the In‐flight Lightning Damage Assessment System (ILDAS) on board of an A340 test aircraft. The aircraft was intentionally flying through a thunderstorm at 12‐km altitude over Northern Australia in January 2016. Two gamma ray detectors showed a significant count rate increase synchronously with fast electromagnetic field variations registered by an on‐board antenna. A sequence of 10 gamma ray enhancements was detected, each lasted for about 1 s. Their spectrum mainly consists of 511‐keV photons and their Compton component. The local electric activity during the emission was identified as a series of static discharges of the aircraft. A full‐scale Geant4 model of the aircraft was created to estimate the emission area. Monte Carlo simulation indicated that the positrons annihilated in direct vicinity or in the aircraft body.

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The strong increase of utilization of CFRP materials in industry has deeply modified the methods of analysis and challenged the numerical tools. In electromagnetism, many issues arise from the replacement of metallic elements by CFRP ones, the main being the protection against direct and indirect effects of lightning. An other important issue is the sizing and optimization of functional current return path on a large structure as an aircraft fuselage. The object of this paper is to present an original approach for studying the current return in a partially metallic fuselage structure covered with CFRP panels in a frequency range comprised between the continuous current up to few tens of kHz. (Abstract) I. PRESENTATION OF THE PROBLEMIn aeronautic industry, metallic structure and fuselage handle the following important roles or functions : signal and fault current return, voltage reference for all electrical equipments, personal protection against electrical shocks, lightning and High Intensity Radiated Fields (HIRF) protection and antenna ground plane reference for the main electrical ones. The use of CFRP materials for fuselage and internal structural elements of an aircraft imposes to assess the correct handling of these functions when all were more easily achieved due to the high electrical conductivity of Aluminum and Titanium alloys. For the functional current (corresponding to the current of functioning equipments that returns through the structure), this results in two main issues. First, poor conducting structure may induce a voltage drop that will be lacking for equipments. Second, depending on the frequency, a certain critical amount of current will flow through CFRP assemblies, or junctions, resulting in local temperature increases with possible mechanical damages. The management of current return distribution over different elements of a large aeronautical structure (fuselage, frames, tracks, cross beams,…) should be tackled with care especially for the aircraft weight optimization. The numerical modeling appears to be an helpful way for current distribution prediction, with the objective to size and optimize the so called Electrical Structure Network (ESN).The critical point in the numerical modeling of such a system is the frequency range of interest. In the case of an aircraft, this range of frequency includes the DC (28V) and goes from 360 to 800 for the 115V AC power supply. This has leaded to analyze different methods available and adapted for such a problematic. II. MODELING STRATEGY A. Numerical methods reviewAfter an evaluation of several methods (FDTD, PEEC,…), our choice has been oriented towards BEM/MOM methods [1,2] for which a specific module has been developed to address the very low frequency range of concern. This choice has been done according to the method capability to model :• CFRP skin covered by metallic mesh• Internal metallic elements• Internal CFRP elements• Several sources with their amplitude and phase• Non-perfect connections (junctions) between internal, interface elements...