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Lightning and static charging tests were performed on one transport aircraft radome and one small aircraft nose radome at the NASA Icing Research Tunnel (IRT), Lewis Research Center, Cleveland, Ohio. The primary purpose of these tests was to evaluate the effects of rain and icing conditions on the lightning protection effectiveness of segmented-type diverters. A secondary purpose was to evaluate the effects of static electrical charges deposited by rain and ice particles. The tests were performed under Task 2.4 of the Joint Program on Improving Lightning and Static Protection of Radomes. Fifty-four lightning tests were performed on two radomes to evaluate the effect of icing, precipitation drop size, and temperature on the ability of segmented diverters to prevent puncture of a radome skin and attachment to the internal radar antenna. Five of the tests resulted in radome puncture under icing conditions. One of the punctures occurred under rain without radome icing.

As part of an update of all of the lightning-related advisory materials for aircraft certification purposes, SAE Committee AE4L and EUROCAE Working Group 31 have completed preparation of a new standard for location of lightning strike zones on aircraft surfaces [Ref. 1]. This new standard is intended to replace the zoning guidelines presently found in US FAA Advisory Circular 20-53A (for fuel systems) and 20-136 (for electronics systems) and in certain military standards, and is known as “the zoning standard”. The new Zoning Standard includes clearer definitions of the lightning strike zones and adds a transition zone between presently defined Zones 1A and 2A. Much of the document addresses the methods to locate the various zones in aircraft and helicopters. This standard, together with a new Environment Standard and updates of the existing FAA AC’s on lightning protection certification, are expected to be formally adopted by the FAA and JAA.

A proposed revision of FAA Advisory Circular AC 20-136 was developed by EUROCAE Working Group 31 and SAE Committee AE4L to address requests by some users of this FAA advisory circular for more specific guidance for selection of equipment transient design levels (ETDL’s) applicable to electrical and avionic systems performing essential or critical functions, and for selection of verification methods for these systems. The proposed revision also makes use of the expanded data base of measured induced transient levels in aircraft since publication of the original draft advisory circular in the United States in 1987 (the original “Orange Book”), to enable descriptions of aircraft interconnecting wiring installations corresponding to each of the standard transient levels.

The proposed revisions of AC 20-136 and AC 20-53A by the SAE and EUROCAE lightning committees do not include the lightning environment parameters as has been the case in the previous version of these AC's. The committees have recently drafted a new “Aircraft Lightning Environment and Related Test Waveforms Standard” known as SAE-AE4L-97-4, the “Purple Book” in the U.S, and EUROCAE ED84 in Europe. This document contains a description of the phenomenology related to aircraft lightning interaction, and all the external parameters of the environment (i.e. current, statistics, repetition rate, etc.) and the associated representative waveforms. Moreover, the definitions of multiple burst and multiple stroke environment have been revisited based on a better understanding of the statistics of lightning.

Measurements of lightning-induced transients in typical electrical circuits installed within a small, conventional aluminum airplane fuselage have been made as part of a comprehensive assessment of the effects of direct lightning strikes and high intensity radiated frequency (HIRF) fields on avionic systems installed within small aircraft. These measurements were conducted in support of development of design guidelines for installation and certification of advanced avionics in small aircraft, under a U.S. National Aeronautics and Space Administration (NASA) sponsored Small Business Innovation Research (SBIR) program aimed at developing technology to enable advanced avionic systems to be installed in new small airplanes or to be retrofitted into existing airplanes. This paper presents examples and summaries of lightning-related magnetic fields and resulting induced voltage and current transients within a small 4-place Mooney aluminum fuselage and engine nacelle.