Protection of Aircraft
Lightning Protection of Aircraft Handbook
By: Franklin A. Fisher and J. Anderson Plumer
Commissioned by the FAA
This is the canonical handbook for engineers seeking to understand the effects of lightning on aircraft as well as practical measures for protecting aircraft against lightning effects.
This handbook has been the basis of instructional courses in lightning protection. The handbook is available as a high-resolution PDF download from here.
Chapter 1: An Introduction to High Voltage Phenomena, deals with the nature of high voltage electrical sparks and arcs and with related processes of electric charge formation, ionization, and spark propagation in air. All of these are factors that affect the way that lightning leaders attach to an aircraft and the way that the hot return stroke arc affects the surface to which it attaches. The material introduces practices and terms used for many years in the electric power industry, but which are not commonly studied by those dealing with aircraft. These terms and practices have, however, affected the tests and practices used to evaluate the effects of lightning on aircraft.
Chapter 2: The Lightning Environment provides an elementary description of cloud electrification and lightning strike formation, and follows with statistics of cloud-to-earth lightning parameters from which the aircraft lightning design and test standards have been derived. The user of this book is urged to study these two introductory chapters before proceeding with later sections of the book. The treatment of these topics is on an elementary level and is aided by simple illustrations, which should enable those with only a limited background in electricity to proceed to an adequate understanding of important principles.
Chapter 3: Aircraft Lightning Attachment Phenomena and Chapter 4: Lightning Effects on Aircraft introduce the reader to the basic mechanisms of naturally occurring and aircraft initiated lightning strikes. The flight conditions when strikes have most frequently occurred, and the types where of affects these strikes may have on the aircraft may be reviewed. Only a very brief mention is made of the potential lightning effects here, since these are the topics of most of the later chapters.
Chapter 5: The Certification Process reviews the history of aircraft lightning protection regulations and standards and introduces the latest versions of these; most notably, the standards for the lightning environment, zoning and testing that have been published and updated by SAE and EUROCAE since 1999. Since further updates of these criteria are expected (SAE, for example, requires that all of its documents must be reviewed every 5 years) the user of this book should always obtain the most recently published versions of each of the requirements and standards documents referenced in this book.
Chapter 6: Protection Against Physical Effects and Chapter 7 – Fuel System Protection contain the basic elements of protection designed for the airframe, fuel tanks, and fuel system components. The methods presented here are basic approaches, and many variations on these, too numerous to describe in this book, have been successfully used. The reader is cautioned that all candidate designs should be tested, especially those that do not have a successful history of prior use. Fuel vapor ignition remains one of the most serious lightning hazards, and should be given careful attention in any design and certification program. It is not possible to verify adequacy of fuel system protection without lightning testing of fuel tanks and systems.
Chapters 8 through 17 focus on protection of electrical and avionic systems against indirect effects and form the basis for our course, Lightning Protection of Avionics. As with all aspects of electromagnetic interference and control, the prevention of damage and interference from lightning becomes more and more critical as aircraft evolve. Most of the navigation and control functions aboard modern aircraft place a computer between the pilot and the control surfaces or engines, often without mechanical backup. This makes it essential that the computer and control equipment be designed to prevent damage or upsets by lightning. Control of these indirect effects requires coordination between those who design the air-frame and its interconnecting wiring, those who design avionic systems and those who oversee the certification process, Part of the overall control process requires the selection of transient design levels and application of suit-able test standards and practices.
Chapter 8 – Introduction to Induced Effects introduces the subject of induced effects and briefly summarizes the subjects covered in more detail in later chapters.
Chapter 9 – Elementary Aspects of Induced Effects covers the basic physics common to the subsequent chapters.
Chapter 10 – The External Electromagnetic Field Environment, covers the external electromagnetic field environment.
Chapter 11 – The Internal Fields Coupled by Diffusion and Redistribution and Chapter 12 – The Internal Fields Coupled through Apertures describe how electromagnetic fields appear inside the airframe, and ways to estimate the magnitudes of these internal fields. These four chapters are the most analytically oriented of the book.
Chapter 13 – Full Vehicle Testing describes the methods available for measuring the transient voltages and cur-rents induced by lightning in aircraft electrical wiring. These are known as “full vehicle” tests and are usually applied at reduced amplitudes so as not to damage the tested airplane.
Chapter 14 – Response of Aircraft Wiring discusses some of the practical problems of calculating the response of aircraft wiring to electromagnetic fields, and provides some examples of how basic principles can be used to estimate the magnitudes of induced transients in simple circuits.
Chapter – 15 Shielding reviews the physics of shielding effectiveness and discusses this important protection approach of shielding of aircraft wiring. This chapter also emphasizes the features that must be included in shield designs that are necessary to realize maximum effective-ness from shields.
Chapter 16 – Design to Minimize Induced Effects discusses some of the policy matters relating to control of indirect effects, tasks that must be undertaken by those responsible for setting overall design practices. Principally these relate to shielding and grounding prac-tices to be followed, and to transient design level specifi-cations to be imposed on vendors.
Chapter 17 – Circuit Design discusses some aspects of circuit design, principally those relating to surge protective devices and methods of analyzing the damage effects of surge voltages and components on electronic devices.
Control of lightning indirect effects by analysis can only be carried so far; proof of tolerance of indirect effects is most likely to come about by performing tests on individ-ual items of equipment and on interconnected systems.
Chapter 18 – Test Techniques for Evaluation of Induced Effects presents an overview of test methods used to verify the ability of equipment to tolerate lightning-induced transients and the ability of complete systems to to tolerate those transients, particularly when applied in the multiple stroke and multiple burst waveform sets. These test methods have recently been incorporated in new or updated lightning test standards. A few comments on personnel safety are also included, since lightning tests involve the generating and applying very high voltages and currents – far exceeding the levels employed in most electrical test laboratories. They also far exceed lethal levels and have proven fatal to inex-perienced operators. Lightning tests to evaluate or verify either direct or indirect effects should be performed only by personnel experienced in this technology.