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【范围】
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This guide provides detailed information, guidance, and methods related to the Federal Aviation Administration (FAA)
Advisory Circular (AC) 20-158 and European Aviation Safety Agency (EASA) draft Advisory Material Joint (AMJ), both
titled "The Certification of Aircraft Electrical and Electronic Systems for Operation in the High-Intensity Radiated Fields
(HIRF) Environment". The AC provides acceptable means, but not the only means, of compliance with Title 14, Code of
Federal Regulations (14 CFR) 23.1308, 25.1317, 27.1317, and 29.1317, High-Intensity Radiated Fields (HIRF) protection
for Aircraft Electrical and Electronic Systems, and applicable FAA HIRF Special Conditions to prevent hazards to aircraft
electrical and electronic systems due to HIRF produced by external transmitters. It is also intended for this guide to
provide the same information, guidance, and methods to the European Aviation Safety Agency (EASA) interim HIRF
policies certification requirements.
This guide is neither mandatory nor regulatory in nature and does not constitute a regulation or legal interpretation of the
regulation. The information in this guide represents a collection of best engineering practices that have been used to
certify aircraft HIRF protection. An applicant may elect to establish an alternative method of compliance that is acceptable
to the cognizant airworthiness authorities.
This document is consistent with the guidance in FAA AC 20-158. The AC 20-158 and draft HIRF AMJ may be
referenced in aircraft certification requirements such as JAA/EASA certification review items. While this document is
generally consistent with AC 20-158 and draft HIRF AMJ, users of this document should verify that the guidance in this
document is acceptable to the cognizant airworthiness authorities.
1.1 Purpose
This document provides technical guidance to demonstrate compliance with aircraft High-Intensity Radiated Field (HIRF)
regulations. This guide may be applied to new aircraft, modification of existing aircraft, and installation of existing systems
on an aircraft that has not previously used that equipment. The HIRF regulations apply to aircraft electrical and electronic
systems, including power distribution systems, electrical generating systems, electronic engine control systems, electronic
flight control systems, and navigation, communication, and flight reference systems. The term 'systems' refers to
electrical and electronic equipment; interconnecting power, signal, and control wiring; indicators; control panels; sensors;
and software.
The HIRF regulations apply to systems installed on transport airplanes, normal and transport category rotorcraft, and
small airplanes. A certification applicant must demonstrate that aircraft systems that perform functions whose failure
could prevent continued safe flight and landing are not adversely affected when the aircraft is exposed to the HIRF
Environment I, II or III, as specified in the regulations. Additionally, systems performing functions related to the ability of
the flight crew and aircraft to operate in adverse operating conditions must not be adversely affected during and after
exposure to equipment test levels specified in the regulations. The approach to achieving HIRF certification is through
appropriate system protection, qualification, and installation.
Aircraft operate in a number of electromagnetic environments. This document, however, only addresses HIRF. For other
electromagnetic environments, reference the appropriate regulations, requirements, standards, and guides.
To avoid confusion with other electromagnetic environments and to provide a means of readily identifying the engineering
associated with these regulations, the term 'high intensity radiated fields' will be used along with the abbreviation HIRF in
this document.
1.2 Aircraft and HIRF
In the past most aircraft used a series of cables, chains, cranks, and mechanical mechanisms to operate the systems
which gave the aircraft its ability to fly. With the advent of the transistor many mechanical devices have been replaced or
augmented with electronic circuits. Electronic circuits have increasingly been designed and used for flight critical aircraft
control systems, due to their ability to accurately control complex functions and increase reliability. Electronic circuits,
however, not only respond to their internal electrical signal flow, but may respond to any input which can couple into the
wire bundles, wires, IC leads, and electrical junctions. The Electromagnetic Environment (EME) is one of these inputs
that by its nature has access to all these electronic circuits and may result in disabling effects called Electromagnetic
Interference (EMI).
Concern for the safety of flight of aircraft employing electrical/electronic systems when subjected to the effects of an
external HIRF environment has increased substantially due to the following principal factors:
a. Greater dependence on electrical/electronic systems performing functions required for continued safe flight and
landing.
b. Possibility of reduced Electromagnetic (EM) shielding afforded by composite materials.
c. Potential increase in susceptibility of integrated circuits due to increased operating speed and density.
d. The expectation that the external RF environment will become increasingly severe due to an increase in the number
and power of RF emitters.
The reliance upon similar redundancy as a means of protection against the effects of HIRF may be negated if the backup
systems are also electronic and susceptible to HIRF.
The aircraft skin and structure have also evolved. The classic aircraft is made of aluminum and titanium structure with an
aluminum skin. Modern technology and the desire to develop more efficient aircraft (the efficiency being an aircraft that
can carry more payload further) have driven the introduction of carbon-epoxy structure, carbon-epoxy skins, and aramid
fiber-epoxy skins in civil aircraft. Aluminum may be a good EM shield against HIRF and hence electronic circuits are
provided inherent protection. However, some composites are poor EM shields, causing HIRF to irradiate the electronic
systems on such aircraft with relatively little attenuation (when compared to aluminum aircraft structure and skin).
This guide stresses the need to balance the HIRF hardening design between equipment and the aircraft to provide
adequate protection from HIRF. The intended result is an aircraft certification wherein the safety of flight will not be
compromised when the aircraft encounters HIRF.strRefField
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