In-flight lightning damage assessment system ILDAS, Tests on-ground and in-flight

The In-flight lightning damage assessment system ILDAS resulted from a EU-FP6 cooperation of 12 partners. It has successfully been completed with demonstration of operation in 2009. Airbus decided to develop the system further with EADS and NLR. The paper describes the magnetic field sensor selected for this phase 2, and briefly discusses the test on-ground and tests in flights through thunderstorms carried out up to now

The EREA Vision on high priority research axes towards air transport system 2050

Europe is writing the future of its air transport in the new Strategic Research and Innovation Agenda. In this open context of building the future of aviation, the research centres have a key role in providing their vision independently of any economic interest. Therefore, the association of the European Research Establishments in Aeronautics (EREA) is committed to provide to the European commission and to the aeronautical community in general its vision on the 2050 air transport system and its recommendations on high priority research axes to be funded in order to pave the way towards 2050. The study briefly presented here has investigated five interdependent technological domains identified as priority and common ones to any scenarios of the future: aircraft configurations, on-board sub-systems, propulsion systems, airport and the automation issue of the air transport system

In-flight measurements of lightning and thunderstorm radiation

Thunderstorms emit bursts of energetic radiation. Moreover, a lightning stepped leader produces x-ray pulses. These phenomena, their interrelation and impact on terrestrial atmosphere and near space are not fully understood yet. The In-flight Lightning Strike Damage Assessment System ILDAS was developed in an EU FP6 project (http://ildas.nlr.nl/) to provide information on threat that lightning poses to aircraft. It is intended to localize the lightning attachment points in order to reduce maintenance time and to build statistics on lightning current. The system consists of one E-field sensor, eight H-field sensors and was recently extended with two LaBr3 scintillation detectors to measure hard radiation inside the aircraft. One of the unique features of the system is the ability to reconstruct a lightning current direction for any instance in time. The x-rays generated by the lightning flash are measured in synchronization better than 10 ns with the lightning current information during a period of 1 second around the strike. Numerous fast x-ray bursts of 1-4 μs duration have been measured. The x-rays occur during initiation phase of lightning leader and during attachment phases of subsequent discharges and return strokes

New high-energy phenomena in aircraft triggered lightning

High-energy phenomena associated with lighting have been proposed in the twenties, observed for the first time in the sixties, and further investigated more recently by e.g. rocket triggered lightning. Similarly, x-rays have been detected in meter-long discharges in air at standard atmospheric conditions. Questions came up whether lightning triggered by aircraft would also generate hard radiation in-flight, its timing with respect to lightning current, its intensity and spectrum. In an earlier project, we developed a system ILDAS (http://ildas.nlr.nl) to determine the lightning current and its pattern over the aircraft with high accuracy and time-resolution. Later we added two x-ray detectors fore and aft in the aircraft.\u3cbr/\u3eIn many flights X-rays were detected indeed associated with lightning strikes. Up to now we could attribute the observed x-rays to the lightning discharge initiation, first due to leader steps in the attachment phase of the lightning channel which lasts several milliseconds, and secondly during several microseconds before the recoil current pulses. Mostly the x-rays appeared to originate from the cathode spot on the aircraft. The required fast electrons are accelerated in the high electric fields in air just before the current starts.\u3cbr/\u3eIn recent flights we observed a new phenomenon, a series of x-rays pulses lasting 8 microseconds, synchronous with the recoil current maximum of about 20 kA. From the current pattern and the relative intensity observed on both detectors, we again concluded that the x-ray originated somewhere in a region near the cathode, which was in this case the tail of the aircraft. The association with the current maximum is remarkable since an arc usually does not go with large electric fields. Arc jumps are a less likely because of the limited aircraft displacement. An alternative explanation is discharge initiation in the vicinity where the aircraft is not a part of that discharge current.\u3cbr/\u3eIn the presentation we will address such phenomena, and also correlate observed currents in the aircraft with ground based measurements. \u3cbr/\u3

In-flight observation of long duration gamma-ray glows by aircraft

Long Gamma-Ray Glow is a long-lasting (several seconds to minutes) X- and gamma radiation presumably originated from high-electric field of thunderclouds. Such glows were previously observed by aircraft, balloons, and from the ground. When detected with other particles, i.e. electrons and neutrons, they are usually called Thunderstorm Ground Enhancements (TGEs). Their measured spectra are often consistent with Relativistic Runaway Electron Avalanche (RREA) mechanism. That is why RREA is a commonly accepted explanation for their existence. The gamma-ray glows are observed to be interrupted by lightning discharge, which terminates the high-electric field region.\u3cbr/\u3eIn January 2016 an Airbus A340 factory test aircraft was performing intentional flights through thunderstorms over Northern Australia. The aircraft was equipped with a dedicated in-flight lightning detection system called ILDAS (www.ildas.nlr.nl). The system also contained two scintillation detectors each with 38x38 mm cylinder LaBr3 crystals. While being at 12 km altitude the system detected a 30-fold gamma-ray flux enhancement. It lasted for 20 seconds and was abruptly terminated by a lightning flash. The flash hit the aircraft and its parameters were recorded with 10 ns sampling time including gamma radiation. Ground-based lightning detection network WWLLN detected 4 strikes in the nearby region, all in association with the same flash. The ILDAS system recorded the time-resolved spectrum of the glow. In 6 minutes, after making a U-turn, the aircraft passed by the same glow. Smaller gamma-ray enhancement was again detected. \u3cbr/\u3eIn this presentation we will show the mapped event timeline including airplane, gamma-ray glow, WWLLN, and cloud data. We will discuss the glow’s properties, i.e. intensity and differential spectrum, and its possible origin. This result will also be compared to previously reported observations. \u3cbr/\u3

Lightning current distribution and hard radiation in aircraft, measured in-flight

The In-flight Lightning Damage Assessment System ILDAS has been presented in EMC Europe in 2012. ILDAS can determine the lightning current distribution on an aircraft with high resolution in time and amplitude. Later the system was extended and included two x-ray detectors to measure the high-energy radiation that is generated in thunderstorms and by lightning proper. It has been flown for many times now. The paper presents a few selected data

Thunderstorm high-energy radiation measured in-flight

High-Energy Atmospheric Physics is a newly emerging branch of physics actively developing at the edge of particle physics, optics, electrodynamics and engineering. Although the thundercloud generation process involves electrostatic charging, a multitude of very dynamic lightning-related discharge processes have been identified recently in and above thunderclouds. They are Terrestrial Gamma-Ray Flashes (TGFs) and Electron Beams (TEBs), a number of Transient Luminous Events (TLEs), and Thundercloud Ground Enhancements (TGEs). The TGFs have immediately after discovery been recognized as the most energetic electromagnetic events in terrestrial atmosphere. Besides it, due to significant advance in optical and electrical registration techniques, lightning initiation, propagation and attachment mechanisms have been only recently understood in better detail.\u3cbr/\u3e\u3cbr/\u3eAt the same time the number of passengers carried by air transport rose by more than 1000% from 0.3 to 3.4 billion in 1970 - 2015. Aircraft themselves greatly progressed in using new materials and sophisticated electronic systems. However, the last public campaign dedicated to the study of lightning interaction with aircraft was ended in the 1980’s. None of the abovementioned phenomena was even known by then.\u3cbr/\u3e\u3cbr/\u3eFrom 2011 till 2016 Airbus factory test aircraft performed intentional thundercloud-penetrating flights in the frame of natural icing test campaigns. The aircraft were equipped with a dedicated in-flight lightning damage assessment system (ILDAS, http://ildas.nlr.nl). The system’s main objectives are to detect any lightning interaction with the aircraft, to localise entry and exit points and to assess the stroke intensity and waveform. From 2013 onwards, the system also carries two LaBr3 scintillation detectors to measure X- and Gamma-Ray radiation synchronously with lightning current. In this work we show experimentally collected data inside the aircraft on various flights near and through thunderstorms. Microsecond-short gamma-ray bursts are detected in association with lightning recoil processes.\u3cbr/\u3e\u3cbr/\u3eParticular new results came in January 2016, when an Airbus A340 factory test aircraft was performing intentional flights through thunderstorms over Northern Australia. While being at 12 km altitude the ILDAS system detected a 30-fold gamma ray flux enhancement. It lasted for 20 seconds and was abruptly terminated by a lightning flash. The terminating flash hit the aircraft and its parameters were recorded with 10 ns sampling time including gamma radiation. Ground-based lightning detection network WWLLN detected 4 strikes in the nearby region, all in association with the same flash. The ILDAS system also recorded the time-resolved spectrum of the glow. Approximately 6 minutes later, the aircraft turned towards another thunderstorm region and a glow with less gamma-ray enhancement was detected.\u3cbr/\u3e\u3cbr/\u3eIn the presentation we will show the mapped event timeline including airplane, gamma-ray glow, WWLLN, and cloud data.\u3cbr/\u3eWe will discuss the glow’s properties, i.e. intensity and differential spectrum, and its possible origin. This result will be compared to previous observations