Advisory U.S. Department of Transportation Circular Federal Aviation Administration Subject: The Certification of Aircraft Electrical and Electronic Systems for Operation in the High-intensity Radiated Fields (HIRF) Environment Date:
Initiated by:
05/30/14 AIR-130 AC No: 20-158A
1. P urpose.
a. This advisory circular (AC) will provide you with information and guidance on how to show 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.
b. This AC is not mandatory and does not constitute a regulation. It describes an acceptable means, but not the only means, for you to show compliance with the requirements for protection of the operation of electrical and electronic systems on an aircraft when the aircraft is exposed to an external HIRF environment. If you use the means described in this AC, you must follow it entirely to comply with this AC. The term “must” is used to indicate mandatory requirements when following the guidance in this AC. The term “should” is used when following the guidance is recommended but not required to comply with this AC.
c. This AC updates AC 20-158 to include the latest revision of SAE ARP 5583A (and EUROCAE document ED-107A), Guide to Certification of Aircraft in a High Intensity Radiated Field (HIRF) Environment, June 2010.
d. AC 20-158, The Certification of Aircraft Electrical and Electronic Systems for Operation in a High-Intensity Radiated Field (HIRF) Environment, dated July 30, 2007, is cancelled.
2. Applicability. This AC applies to all applicants for a new type certificate (TC) or a change to an existing TC when the certification basis requires you to address the HIRF certification requirements of 14 CFR 23.1308, 25.1317, 27.1317, and 29.1317.
3. Related Material.
a. 14 CFR. Sections 23.1308, 25.1317, 27.1317, and 29.1317, High-intensity Radiated Fields (HIRF) protection; §§ 23.1309, 25.1309, 27.1309, and 29.1309, Equipment, systems, and installations; §§ 23.1529, 25.1529, 27.1529, and 29.1529, Instructions for Continued Airworthiness; § 25.1729, Instructions for Continued Airworthiness: EWIS; and § 26.11,
Electrical Wiring Interconnection Systems (EWIS) Maintenance Program, (when the latest regulation is not required). You can get copies of the above 14 CFR sections from the Superintendent of Documents, Government Printing Office, Washington, D.C. 20402-9325, telephone 202-512-1800, fax 202-512-2250. You can also get copies from the Government Printing Office (GPO) website at www.access.gpo.gov.
b. European Aviation Safety Agency (EASA). Certification Specifications (CS)-23, Normal, utility, aerobatic & commuter aeroplanes, CS-25, Large aeroplanes, CS-27, Small rotorcraft, and CS-29, Large rotorcraft. You can get copies of these documents from the European Aviation Safety Agency, Postfach 10 12 53, D-50452 Köln, Germany; telephone +49 221 8999 000; fax: +49 221 8999 099; website: http://www.easa.eu.int.
c. FAA ACs. AC 23.1309-1E, System Safety Analysis and Assessment for Part 23 Airplanes; AC 25.1309-1A, System Design and Analysis; AC-27-1B, Certification of Normal Category Rotorcraft; and AC-29-2C, Certification of Transport Category Rotorcraft, or later revisions. You can view and download copies from our web based Regulatory and Guidance Library (RGL) at www.airweb.faa.gov. On the RGL website, select “Advisory Circular”, then select “By Number”. ACs are also available on the FAA website:
http://www.faa.gov/regulations_policies/advisory_circulars/.
d. RTCA, Inc. RTCA/DO-160, Environmental Conditions and Test Procedures for Airborne Equipment, Revision E or later. You can order copies of this document from RTCA, Inc., 1150 18th St. NW, Suite 910, Washington, DC 20036; telephone: (202) 833-9339 or fax
(202) 833-9434. You can also order copies online at http:/www.rtca.org. This document is technically equivalent to EUROCAE ED-14. You may use RTCA/DO-160 whenever there is a reference to EUROCAE ED-14 in this AC.
e. European Organization for Civil Aviation Equipment (EUROCAE). You can order copies of the following documents from EUROCAE, 102 rue Etienne Dolet, 92240 Malakoff, France; Telephone: +33 1 40 92 79 30; Fax: +33 1 46 55 62 65; website: http://www.eurocae.net.
(1) EUROCAE ED-107A, Guide to Certification of Aircraft in a High Intensity Radiated Field (HIRF) Environment, July 2010. ED-107A and SAE ARP 5583A, referenced in paragraph 3f(1) below, are technically equivalent. Either document may serve as the "User’s Guide" referred to in this AC.
(2) EUROCAE ED-14, Environmental Conditions and Test Procedures for Airborne Equipment, Revision E or later. This document is technically equivalent to RTCA/DO-160. You may use EUROCAE ED-14 whenever there is a reference to RTCA/DO-160 in this AC.
f. SAE International. You can order copies of the following documents from SAE World Headquarters, 400 Commonwealth Drive, Warrendale, Pennsylvania 15096-0001;
telephone (724) 776-4970; fax 724-776-0790; web site: http://www.sae.org.
(1) SAE Aerospace Recommended Practice (ARP) 5583A, Guide to Certification of Aircraft in a High Intensity Radiated Field (HIRF) Environment, June 2010. SAE ARP 5583A 2
and ED-107A, referenced in paragraph 3.e(1) above, are technically equivalent. Either document may serve as the "User’s Guide" referred to in this AC.
(2) SAE ARP 4754A, Guidelines for Development of Civil Aircraft and Systems, December 2010.
(3) SAE ARP 4761, Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment, December 1996.
4. Background.
a. Aircraft Protection. Concern for the protection of aircraft electrical and electronic systems has increased substantially in recent years for the following reasons:
(1) Greater dependence on electrical and electronic systems performing functions required for continued safe flight and landing of an aircraft;
(2) Reduced electromagnetic shielding afforded by some composite materials used in aircraft designs;
(3) Increased susceptibility of electrical and electronic systems to HIRF because of increased data bus and processor operating speeds, higher density integrated circuits and cards, and greater sensitivities of electronic equipment;
(4) Expanded frequency usage, especially above 1 gigahertz (GHz);
(5) Increased severity of the HIRF environment because of an increase in the number and radiated power of radio frequency (RF) transmitters; and
(6) Adverse effects experienced by some aircraft when exposed to HIRF.
b. HIRF Environment. The electromagnetic HIRF environment exists because of the transmission of electromagnetic RF energy from radar, radio, television, and other ground-based, shipborne, or airborne RF transmitters. The User's Guide (SAE ARP 5583A/EUROCAE ED-107A) provides a detailed description of the derivation of these HIRF environments.
5. Definitions.
a. Adverse Effect. HIRF effect that results in system failure, malfunction, or misleading information to a degree that is unacceptable for the specific aircraft function or system addressed in the HIRF regulations. A determination of whether a system or function is adversely affected should consider the HIRF effect in relation to the overall aircraft and its operation.
b. Attenuation. Term used to denote a decrease in electromagnetic field strength in transmission from one point to another. Attenuation may be expressed as a scalar ratio of the input magnitude to the output magnitude or in decibels (dB).
c. Automatically Recover. Return to normal operations without pilot action.
d. Bulk Current Injection (BCI). Method of electromagnetic interference (EMI) testing that involves injecting current into wire bundles through a current injection probe.
e. Continued Safe Flight and Landing. Capability for continued controlled flight and landing at a suitable location, possibly using emergency procedures, but without requiring exceptional pilot skill or strength. Some aircraft damage may be associated with a failure condition during flight or upon landing.
f. Continuous Wave (CW). RF signal consisting of only the fundamental frequency with no modulation in amplitude, frequency, or phase.
g. Coupling. Process whereby electromagnetic energy is induced in a system by radiation produced by an RF source.
h. Current Injection Probe. Inductive device designed to inject RF signals directly into wire bundles when clamped around them.
i. Direct Drive Test. EMI test that involves electrically connecting a signal source directly to the unit being tested.
j. Equipment. Component of an electrical or electronic system with interconnecting electrical conductors.
k. Equipment Electrical Interface. Location on a piece of equipment where an electrical connection is made to the other equipment in a system of which it is a part. The electrical interface may consist of individual wires or wire bundles that connect the equipment.
l. External HIRF Environment. Electromagnetic RF fields at the exterior of an aircraft.
m. Field Strength. Magnitude of the electromagnetic energy propagating in free space expressed in volts per meter (V/m).
n. HIRF Environment. Electromagnetic environment that exists from the transmission of high power RF energy into free space.
o. HIRF Vulnerability. Susceptibility characteristics of a system that cause it to suffer adverse effects when performing its intended function as a result of having been subjected to a HIRF environment.
p. Immunity. Capacity of a system or piece of equipment to continue to perform its intended function, in an acceptable manner, in the presence of RF fields.
q. Interface Circuit. Electrical or electronic device connecting the electrical inputs and outputs of equipment to other equipment or devices in an aircraft.
r. Internal HIRF Environment. The RF environment inside an airframe, equipment enclosure, or cavity. The internal RF environment is described in terms of the internal RF field strength or wire bundle current.
s. Margin. Difference between equipment susceptibility or qualification levels and the aircraft internal HIRF environment. Margin requirements may be specified to account for uncertainties in design, analysis, or test.
t. Modulation. Process whereby certain characteristics of a wave, often called the carrier wave, are varied in accordance with an applied function.
u. Normal Operation. A status where the system is performing its intended function.
Specifically in the context of §§ 23.1308(a)(2), 25.1317(a)(2), 27.1317(a)(2), and 29.1317(a)(2) normal operation is defined as the ability to perform functions to the extent necessary to continue safe flight and landing, but not necessarily full functional performance.
v. Radio Frequency (RF). Frequency useful for radio transmission. The present practical limits of RF transmissions are roughly 10 kilohertz (kHz) to 100 gigahertz (GHz). Within this frequency range, electromagnetic energy may be detected and amplified as an electric current at the wave frequency.
w. Reflection Plane. Conducting plate that reflects RF signals.
x. Similarity. Process of using existing HIRF compliance documentation and data from a system or aircraft to demonstrate HIRF compliance for a nearly identical system or aircraft of equivalent design, construction, and installation.
y. Susceptibility. Property of a piece of equipment that describes its inability to function acceptably when subjected to unwanted electromagnetic energy.
z. Susceptibility Level. Level where the effects of interference from electromagnetic energy become apparent.
aa. System. Piece of equipment connected via electrical conductors to another piece of equipment, both of which are required to make a system function. A system may contain pieces of equipment, components, parts, and wire bundles.
bb. Transfer Function. Ratio of the electrical output of a system to the electrical input of a system, expressed in the frequency domain. For HIRF, a typical transfer function is the ratio of the current on a wire bundle to the external HIRF field strength, as a function of frequency.
cc. Upset. Impairment of system operation, either permanent or momentary. For example, a change of digital or analog state that may or may not require a manual reset.
dd. User’s Guide. Refers to SAE document ARP 5583A or EUROCAE document ED-107A.
6. Approaches to Compliance.
a. General. The following activities should be elements of a proper HIRF certification program. Adherence to the sequence shown is not necessary. More detailed information on HIRF certification compliance is provided in the User’s Guide. You should:
(1) Identify the systems to be assessed;
(2) Establish the applicable aircraft external HIRF environment;
(3) Establish the test environment for installed systems;
(4) Apply the appropriate method of HIRF compliance verification; and,
(5) Verify HIRF protection effectiveness.
b. Identify the Systems to be Assessed.
(1) General. You must identify aircraft systems requiring HIRF assessment. You should define the elements of the system performing a function, considering redundant or backup equipment that makes up the system. The process used for identifying these systems should be similar to the process for showing compliance with 14 CFR 23.1309, 25.1309, 27.1309, and
29.1309, as applicable. These sections address any system failure that may cause or contribute to an effect on the safety of flight of an aircraft. The effects of a HIRF encounter should be assessed to determine the degree to which the aircraft and its systems safety may be affected.
The operation of the aircraft systems should be assessed separately and in combination with, or in relation to, other systems. This assessment should cover:
(a) All normal aircraft operating modes, stages of flight, and operating conditions;
(b) All failure conditions and their subsequent effect on aircraft operations and the flightcrew; and
(c) Any corrective actions required.
(2) Safety Assessment. A safety assessment related to HIRF must be performed to establish and classify the equipment or system failure condition. Table 1 provides the corresponding failure condition classification and system HIRF certification level for the appropriate HIRF regulations. The failure condition classifications and terms used in this AC are similar to those used in AC 23.1309-1E, AC 25.1309-1A, AC-27-1B, and AC-29-2C, as applicable. Only those systems identified as performing or contributing to functions whose failure would result in catastrophic, hazardous, or major failure conditions are subject to HIRF regulations. Based on the failure condition classification established by the safety assessment, the systems should be assigned appropriate HIRF certification levels, as shown in table 1. The safety assessment should consider the common cause effects of HIRF, particularly for highly integrated systems and systems with redundant elements. Further guidance on performing the safety assessment can be found in AC 23.1309-1E, AC 25.1309-1A, AC-27-1B, AC-29-2C, SAE ARP 4754A, SAE ARP 4761, and ARP 5583A.
Table 1. HIRF Failure Conditions and System HIRF Certification Levels
HIRF REQUIREMENTS EXCERPTS FROM §§ 23.1308, 25.1317, 27.1317, AND 29.1317 Each electrical and electronic system that performs a function whose failure would prevent the continued safe flight and landing of the rotorcraft/airplane
FAILURE
CONDITION
Catastrophic
SYSTEM HIRF
CERTIFICATION
LEVEL
A Each electrical and electronic system that performs a function whose failure would significantly reduce the
capability of the rotorcraft/airplane or the ability of Hazardous B the flightcrew to respond to an adverse operating
condition
Each electrical and electronic system that performs a function whose failure would reduce the capability of Major C the rotorcraft/airplane or the ability of the flightcrew to respond to an adverse operating condition
(3) Failure Conditions. Your safety assessment should consider all potential adverse effects due to system failures, malfunctions, or misleading information. The safety assessment may show some systems have different failure conditions in different phases of flight; therefore, different HIRF requirements may have to be applied to the system for different phases of flight.
For example, an automatic flight control system may have a catastrophic failure condition for autoland, while automatic flight control system operations in cruise may have a hazardous failure condition.
c. Establish the Applicable Aircraft External HIRF Environment. The external HIRF environments I, II, and III, as published in 14 CFR 23.1308, 25.1317, 27.1317, and 29.1317, are shown in tables 2, 3, and 4, respectively. The field strength values for the HIRF environments and test levels are expressed in root-mean-square (rms) units measured during the peak of the modulation cycle.
Table 2. HIRF Environment I
FREQUENCY FIELD STRENGTH (V/m)
PEAK AVERAGE 10 kHz 2 MHz 50 50 2 MHz 30 MHz 100 100 30 MHz - 100 MHz 50 50 100 MHz – 400 MHz 100 100 400 MHz – 700 MHz 700 50 700 MHz 1 GHz 700 100 1 GHz 2 GHz 2,000 200 2 GHz 6 GHz 3,000 200 6 GHz 8 GHz 1,000 200 8 GHz 12 GHz 3,000 300 12 GHz 18 GHz 2,000 200 18 GHz 40 GHz 600 200 In this table, the higher field strength applies at the frequency band edges.
Table 3. HIRF Environment II
FREQUENCY FIELD STRENGTH (V/m)
PEAK AVERAGE 10 kHz – 500 kHz 20 20 500 kHz 2 MHz 30 30 2 MHz 30 MHz 100 100 30 MHz – 100 MHz 10 10 100 MHz – 200 MHz 30 10 200 MHz – 400 MHz 10 10 400 MHz 1 GHz 700 40 1 GHz 2 GHz 1,300 160 2 GHz 4 GHz 3,000 120 4 GHz 6 GHz 3,000 160 6 GHz 8 GHz 400 170 8 GHz 12 GHz 1,230 230 12 GHz 18 GHz 730 190 18 GHz 40 GHz 600 150 In this table, the higher field strength applies at the frequency band edges.
Table 4. HIRF Environment III
FREQUENCY FIELD STRENGTH (V/m)
PEAK AVERAGE 10 kHz – 100 kHz 150 150 100 kHz – 400 MHz 200 200 400 MHz – 700 MHz 730 200 700 MHz 1 GHz 1,400 240 1 GHz 2 GHz 5,000 250 2 GHz 4 GHz 6,000 490 4 GHz 6 GHz 7,200 400 6 GHz 8 GHz 1,100 170 8 GHz - 12 GHz 5,000 330 12 GHz - 18 GHz 2,000 330 18 GHz - 40 GHz 1,000 420 In this table, the higher field strength applies at the frequency band edges.
d. Establish the Test Environment for Installed Systems.
(1) General. The external HIRF environment will penetrate the aircraft and establish an internal RF environment to which installed electrical and electronic systems will be exposed.
The resultant internal RF environment is caused by a combination of factors, such as aircraft seams and apertures, reradiation from the internal aircraft structure and wiring, and characteristic aircraft electrical resonance.
(2) Level A Systems. The resulting internal HIRF environments for level A systems are determined by aircraft attenuation to the external HIRF environments I, II, or III, as defined in 14 CFR part 23 appendix J, 14 CFR part 25 appendix L, 14 CFR part 27 appendix D, and 14 CFR part 29 appendix E, as applicable. The attenuation is aircraft- and zone-specific and should be established by aircraft test, analysis, or similarity. The steps for showing level A HIRF compliance are presented in paragraph 9 of this AC.
(3) Level B Systems. The internal RF environments for level B systems are defined in 14 CFR part 23 appendix J, 14 CFR part 25 appendix L, 14 CFR part 27 appendix D, and 14 10
CFR part 29 appendix E, as applicable, as equipment HIRF test levels 1 or 2. The steps for showing level B HIRF compliance are presented in paragraph 10 of this AC.
(4) Level C Systems. The internal RF environment for level C systems is defined in 14 CFR part 23 appendix J, 14 CFR part 25 appendix L, 14 CFR part 27 appendix D, and 14 CFR part 29 appendix E, as applicable, as equipment HIRF test level 3. The steps for showing level C HIRF compliance are also presented in paragraph 10 of this AC.
e. Apply the Appropriate Method of HIRF Compliance Verification.
(1) General. Table 5 summarizes the relationship between the aircraft performance requirements in the HIRF regulations (sections (a), (b) and (c)), and the HIRF environments and test levels. The process for showing compliance with section (d) of the HIRF regulations is discussed in paragraph 6g below.
(2) Pass/Fail Criteria. Establish specific HIRF compliance pass/fail criteria for each system as it relates to the applicable HIRF regulation performance criteria. The definitions of “normal operation” and “automatically recover” in paragraph 5 this AC are provided in the context of §§ 23.1308(a)(2), 25.1317(a)(2), 27.1317(a)(2), and 29.1317(a)(2). These pass/fail criteria should be presented to the FAA for approval. The means for monitoring system performance relative to these criteria should be established by the applicant and approved by the FAA. All effects defining the pass/fail criteria should be the result of identifiable and traceable analysis that includes both the separate and interdependent operational characteristics of the systems. The analysis should evaluate the failures, either singularly or in combination, which could adversely affect system performance. This should include failures which could negate any system redundancy or influence more than one system performing the same function.
HIRF FAILURE CONDITION FROM §§ 23.1308, 25.1317, 27.1317, AND 29.1317 Each electrical and electronic system that performs a function whose failure would prevent the continued safe flight and landing of the airplane/rotorcraft must be designed and installed so that— Each electrical and electronic system that performs a function whose failure would significantly reduce the capability of the airplane/rotorcraft or the ability of the flightcrew to respond to an adverse operating condition must be designed and installed so that— Each electrical and electronic system that performs such a function whose failure would reduce the capability of the airplane/rotorcraft or the ability of the flightcrew to respond to an adverse operating condition must be designed and installed so that—
PERFORMANCE CRITERIA Each function is not adversely affected during and after the time… Each electrical and electronic system automatically recovers normal operation of that function, in a timely manner after… Each electrical and electronic system is not adversely affected during and after… Each function required during operation under visual flight rules is not adversely affected during and after… The system is not adversely affected when… The system is not adversely affected when…
ITEM THE HIRF
ENVIRONMENT OR TEST ENVIRONMENT
LEVEL APPLIES TO OR TEST LEVEL is exposed to HIRFthe airplane/rotorcraft… environment I.
is exposed to HIRF environment I, unless this conflicts with the airplane/rotorcraft… other operational or functional requirements of that system.
is exposed to HIRFthe airplane/rotorcraft… environment II.
is exposed to HIRF environment IIIthe rotorcraft… (Parts 27 and 29 only).
is exposed to the equipment providing these equipment HIRF testfunctions… level 1 or 2.
is exposed to the equipment providing these equipment HIRF testfunctions… level 3.
05/30/14 AC 20-158A Table 5. HIRF Certification Requirements Summary