C Advisory Circular U.S. Department of Transportation Federal Aviation Administration Subject: The Certification of Aircraft AC No: 20-158B Change: (Editorial) Electrical and Electronic Systems for Date: 5/20/24 Updated:
8/12/26 Initiated By: AIR-626 Opera tion in the High-Intensity Radiated Fields (HIRF) Environment This advisory circular (AC) will provide information and guidance on how to show compliance with §§ 23.1308 (Amendment 23-57), 23.2520 (Amendment 23-65), 25.1317,
27.1317, and 29.1317 of title 14, Code of Federal Regulations (14 CFR) for the certification of aircraft electrical and electronic systems for operation in the high-intensity radiated fields (HIRF) environment.
DANIEL J.
ELGAS Digitally signed by DANIEL J. ELGAS Date: 2024.05.20 13:06:51 -04'00' Daniel J. Elgas Director, Policy and Standards Division Aircraft Certification Service
Table of Contents Paragraph Page
1 Purpose1
2 Applicability1
3 Cancellation1
4 Related Material2
4.1 Title 14, Code of Federal Regulations (14 CFR).2
4.2 FAA Advisory Circulars2
4.3 FAA Policy Statement2
4.4 ASTM Consensus Standards3
4.5 European Union Aviation Safety Agency (EASA).3
4.6 RTCA3
4.7 European Organization for Civil Aviation Equipment (EUROCAE).3
4.8 Society of Automotive Engineers (SAE) International.4
5 Definitions4
6 Background7
6.1 HIRF Environment7
6.2 Aircraft Protection7
7 Steps For Showing compliance8
7.1 HIRF Certification Program8
7.2 Identify the Systems to be Assessed.8
7.3 HIRF Safety Assessment8
7.4 Establish the Applicable Aircraft External HIRF Environment.11
7.5 Establish the Test Environment for Installed Systems.13
7.6 Apply the Appropriate Method of HIRF Compliance Verification.14
7.7 Verify HIRF Protection Effectiveness.17
7.8 Previously Issued HIRF Special Conditions.17
8 Margins17
9 HIRF Compliance17
9.1 HIRF Compliance Plan17
9.2 HIRF Verification Test, Analysis, or Similarity Plan.18
9.3 Compliance Reports19
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9.4 Methods of Compliance Verification20
10 Steps to Level A System HIRF Compliance24
10.1 Step 1 — HIRF Safety Assessment.24
10.2 Step 2 — Define Aircraft and System HIRF Protection.25
10.3 Step 3 — System Assessment Decision.25
10.4 Step 4 — Equipment Test26
10.5 Step 5 — Integrated System Test.26
10.6 Step 6 — System Similarity Assessment.28
10.7 Step 7 — Aircraft Assessment Decision.29
10.8 Step 8 — Aircraft Test Decision.29
10.9 Step 9 — Aircraft High-Level Tests30
10.10 Step 10 — Aircraft Low-Level Coupling Tests31
10.11 Step 11 — Generic Transfer Functions and Attenuation - Display Systems Only33
10.12 Step 12 — Aircraft Similarity Assessment.34
10.13 Step 13 — Assess Immunity34
10.14 Step 14 — Corrective Measures36
10.15 Step 15 — HIRF Protection Compliance36
10.16 Compliance for HCL A Systems on Level 1, 2, 3, and 4 Airplanes Ce rtificated Under
Part 2336
11 Steps to Level B and C System HIRF Compliance37
11.1 Step 1 — System Safety Assessment38
11.2 Step 2 — Define Aircraft and System HIRF Protection.38
11.3 Step 3 — Select Compliance Method38
11.4 Step 4 — Equipment Test38
11.5 Step 5 — Similarity Assessment39
11.6 Step 6 — Assess Immunity39
11.7 Step 7 — Corrective Measures40
11.8 Step 8 — HIRF Protection Compliance.40
12 Maintenance, Protection Assurance, and Modifications40
iii
Tables
Table 1. HIRF Failure Conditions and System HIRF Certification Levels10
Table 2. HIRF Environment I12
Table 3. HIRF Environment II12
Table 4. HIRF Environment III13
Table 5. HIRF Certification Requirements Summary for Parts 23 (Amendment 23 -57), 25, 27,
and 2915
Table 6. HIRF Certification Requirements Summary for Part 23 (Amendment 23 -65)16
Figures
Figure 1. Routes to HIRF Compliance – Level A Systems21
Figure 2. Aircraft Low-Level Coupling Tests – Level A Systems22
Figure 3. Routes to HIRF Compliance – Level B and C Systems23
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1 PURPOSE
1.1 This AC provides guidance 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 §§ 23.1308 (Amendment 23-57), 23.2520 (Amendment 23-65),
25.1317, 27.1317, or § 29.1317.
1.2 This revision incorporate s recommendations from the Certification Authorities for Transport Airplanes. These recommendations address inconsistencies in the interpretation and application of the HIRF rules and provide a harmonized compliance approach for transport category airplanes .
1.3 Additionally, this AC contains guidance from the Federal Aviation Administration (FAA) policy statement, PS-ACE-23-10, HIRF/Lightning Test Levels and Compliance Methods for 14 CFR Part 23 Class I, II, and III Airplanes , dated October 3, 2017, which describes an acceptable means on how to show compliance with §§ 23.1308 (Amendment 23-57) and 23.2520. The applicant may also use a means of compliance, which may include consensus standards, accepted by the FAA under § 23.2010.
2 APPLICABILITY
2.1 The guidance provided in this AC is for manufacturers, modifiers, foreign regulatory authorities, and FAA engineers, and their designees .
2.2 The contents of this AC do not have the force and effect of law and are not meant to bind the public in any way . This AC is intended only to provide information to the public regarding existing requirements under the law or agency policies. Conformity with the guidance is voluntary only and nonconformity will not affect rights and obligations under existing statues and regulations. The FAA will consider other methods of demonstrating compliance that an applicant may elect to present. Terms such as “should,” “may,” and “must” are used only in the sense of ensuring applicability of this particular method of compliance when the acceptable metho d of compliance in this document is used. If the FAA becomes aware of circumstances in which following this AC would not result in compliance with the applicable regulations, the FAA may require additional substantiation as the basis for finding compliance .
2.3 This material does not change or create any additional regulatory requirements or authorize changes in or permit deviations from existing regulatory requirements.
3 CANCELLATION This AC cancels AC 20-158A, The Certification of Aircraft Electrical and Electronic Systems for Operation in a High -intensity Radiated Field (HIRF) Environment , dated May 30, 2014.
4 RELATED MATERIAL
4.1 Title 14, Code of Federal Regulations ( 14 CFR).
The full text of these regulations is available at https://www.ecfr.gov.
• Section 23.1308 (Amendment 23-57), High-intensity Radiated Fields (HIRF) Protection.
• Section 23.1529, Instructions for Continued Airworthiness .
• Section 23.2000, Applicability and definitions.
• Section 23.2520 (Amendment 23-65), High-intensity Radiated Fields (HIRF) Protection.
• Section 25.1317, High-intensity Radiated Fields (HIRF) Protection .
• Section 25.1529, Instructions for Continued Airworthiness .
• Section 25.1729, Instructions for Continued Airworthiness: EWIS .
• Section 26.11, Electrical wiring interconnection systems (EWIS) maintenance program.
• Section 27.1317, High-intensity Radiated Fields (HIRF) Protection .
• Section 27.1529, Instructions for Continued Airworthiness.
• Section 29.1317, High-intensity Radiated Fields (HIRF) Protection.
• Section 29.1529, Instructions for Continued Airworthiness .
4.2 FAA Advisory Circulars.
The following FAA ACs are related to the guidance in this AC. You should refer to the latest AC version for guidance, which is available on the Dynamic Regulatory System (DRS) at https://drs.faa.gov/browse .
• AC 21-16, RTCA Document DO-160 versions E, F, and G, Environmental Conditions and Test Procedures for Airborne Equipment .
• AC 23.1309-1, System Safety Analysis and Assessment for Part 23 Airplanes .
• AC 25.1309-1, System Design and Analysis.
• AC 27-1, Certification of Normal Category Rotorcraft .
• AC 29-2, Certification of Transport Category Rotorcraft .
• AC 33.28-3, Guidance Material For 14 CFR§ 33.28, Engine Control Systems .
4.3 FAA Policy Statement.
The following FAA policy statement is related to the guidance in this AC. If the policy statement is revised after publication of this AC, you should refer to the latest version for guidance, which is available on the DRS at https://drs.faa.gov/browse .
PS-ACE-23-10, HIRF/Lightning Test Levels and Compliance Methods for 14 CFR Part 23 Class I, II, and III Airplanes .
4.4 ASTM Consensus Standards.
FAA-accepted consensus standards for part 23 airplanes, including any required changes for acceptance, are available online at https://www.faa.gov/aircraft/air_cert/design_approvals/small_airplanes/small_airplanes _regs.
• FAA Accepted Means of Compliance for Part 23 Airplanes ( Pre-Amendment 23-
64).
• FAA Accepted Means of Compliance for Part 23 Airplanes ( Amendment 23-64 or later).
4.5 European Union Aviation Safety Agency (EASA).
The following certification specification (CS) documents can be ordered by mail at Postfach 10 12 53, D-50452 Cologne, Germany; telephone +49 221 8999 000; fax: +49 221 8999 099; or obtained online at https://www.easa.europa.eu/home .
• CS-23, Normal-Category Aeroplanes.
• CS-25, Large Aeroplanes.
• CS-27, Small Rotorcraft.
• CS-29, Large Rotorcraft.
4.6 RTCA.
The following RTCA (formerly Radio Technical Commission for Aeronautics) document is related to the guidance in this AC. Unless otherwise specified, use the latest FAA-accepted revision for guidance . If the document is revised after publication of this AC, you should verify that the FAA accepts the subsequent revision or update as an acceptable form of guidance. This document can be ordered online at https://www.rtca.org.
RTCA/DO-160E, Environmental Conditions and Test Procedures for Airborne Equipment.
Note: Installers may use section 20, Radio Frequency Susceptibility (Radiated and Conducted), of RTCA/DO-160E, as specified in AC 21-16. RTCA/DO-160E and EUROCAE ED-14E, referenced below, are technically equivalent . You may use RTCA/DO-160E whenever there is a reference to EUROCAE ED -14E in this AC.
4.7 European Organization for Civil Aviation Equipment (EUROCAE) .
The following EUROCAE documen ts are related to the guidance in this AC. Unless otherwise specified, use the latest FAA -accepted revision for guidance . If the document is revised after publication of this AC, you should verify that the FAA accepts the 3
subsequent revision or update as a n acceptable form of guidance. The documents are available online at: https://www.eurocae.net.
• EUROCAE ED-14E, Environmental Conditions and Test Procedures for Airborne Equipment.
• EUROCAE ED-107A, Guide to Certification of Aircraft in a High Intensity Radiated Field (HIRF) Environment .
Note: ED-107A and SAE ARP5583A, referenced below, are technically equivalent.
This AC means either document when referring to “the user’s guide.” EUROCAE ED- 14E and RTCA/DO-160E are technically equivalent . You may use EUROCAE ED-14E whenever there is a reference to RTCA/DO -160E in this AC.
4.8 Society of Automotive Engineers (SAE) International.
The following SAE Aerospace Recommended Practice (ARP) documents are related to the guidance in this AC. Unless otherwise specified, use the latest FAA -accepted revision for guidance. If the document is revised after publication of this AC, you should verify that the FAA accepts the subsequent revision o r update as an acceptable form of guidance. The documents are available online at: https://www.sae.org.
• SAE ARP4754A, Guidelines for Development of Civil Aircraft and Systems .
• SAE ARP4761, Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment .
• SAE ARP5583A, Guide to Certification of Aircraft in a High -Intensity Radiated Field (HIRF) Environment.
Note: SAE ARP5583A and EUROCAE ED-107A, referenced above, are technically equivalent. This AC means either document when referring to “the user’s guide.”
5 DEFINITIONS
• Adverse Effect. A response (caused by exposure to HIRF) that results in an unexpected and unacceptable operation of an aircraf t system, or in an unexpected and unacceptable operation of a function performed by the system .
• Attenuation. 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).
• Automatically Recover . To return to normal operations without flightcrew action.
• Bulk Current Injection (BCI). A method of electromagnetic interference (EMI) testing that involves injecting current in to wire bundles through a current injection probe.
• Channel. A subset of a system consisting of equipment, components, and interconnections, which performs an aircraft function provided by the system. A system could be composed of redundant similar or dissimilar channels to maintain the function at the aircraft level in case of failure on one or several channels.
• 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 strengt h. Some aircraft damage may occur because of a failure condition during flight or on landing. For part 23 airplanes, it is not necessary to land at an airport. For part 25 air planes, the pilot must be able to land safely at a suitable airport. For part 27 and part 29 rotorcraft, the rotorcraft must continue to cope with adverse operating conditions, and the pilot must be able to land safely at a suitable site.
Note: The above definition should be used, regarding the method provided by this AC, for all aircraft except normal category airplanes with a part 23 (Amendment 23-64 or later) certification basis, for which the definition of “continued safe flight and landing” in § 23.2000(b) applies.
• Continuous Wave (CW). Radio frequency (RF) signal consisting of only the fundamental frequency with no modulation in amplitude, frequency, or phase.
• Coupling. Process whereby electromagnetic energy is induced in a system by radiation produced by a RF source.
• Current Injection Probe. Inductive device designed to inject RF signals directly into wire bundles when clamped around them.
• Direct Drive Test. EMI test that involves electrically connecting a signal source directly to the unit being tested.
• Electrical and Electronic System. An electrical and electronic system means all electrical and electronic equipment, components, and the electrical interconnections that are required to perform a particular function.
• Equipment. Component of an electrical and electronic system with interconnecting electrical conductors.
• 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.
• External HIRF Environment . Electromagnetic RF fields at the exterior of an aircraft.
• Field Strength. Magnitude of the electromagnetic energy propagating in free space expressed in volts per meter (V/m).
• Function. The specific action of a system, equipmen t, and flightcrew performance aboard the aircraft that, by itself, provides a completely recognizable operational capability. For example, “display aircraft heading to the pilots ” is a function. One or more systems may perform a specific function, or one s ystem may perform multiple functions.
• HIRF Environment. Electromagnetic environment created by the transmission of high-power RF energy into free space.
• HIRF Vulnerability. Susceptibility characteristics of a system that cause it to suffer adverse effects when performing its intended function because of having been subjected to a HIRF environment.
• 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.
• Interface Circuit. Electrical or electronic device connecting the electrical inputs and outputs of equipment to other equipment or devices in an aircraft.
• Internal HIRF Environment . The RF environment inside an airframe, equipment bay, or cavity. The internal RF environment is described in terms of the internal RF field strength or wire bundle current.
• Margin. Difference between equipment susceptibility or qualification levels and th e aircraft internal HIRF environment. Margin requirements may be specified to account for uncertainties in design, analysis, or test.
• Modulation. Process whereby certain characteristics of a wave, often called the carrier wave, are varied in accordance wit h an applied function.
• Normal Operation. The status where the system is performing its intended function.
When addressing compliance with §§ 23.1308(a)(2), 23.2520(a)(2), 25.1317(a)(2),
27.1317(a)(2), and 29.1317(a)(2), the function whose failure may prevent the continued safe flight and landing should be in the same undisturbed state as before exposure to the HIRF environment.
• Non-Normal Situation. An event, condition, or situation that requires non -normal, abnormal, emergency, or unusual procedures or con figurations for operating the aircraft.
• Pulse Modulation. RF signal in the form of pulses with varied amplitudes and widths (narrowband or broadband).
• Radio Frequency. Frequency within the range used for radio transmission. The present practical range 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.
• Reflection Plane. Conducting plate that reflects RF signals.
• 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 desig n, construction, and installation having equivalent internal and external environmental conditions .
• Square Wave. RF signal that alternates amplitude, with the same duration, between fixed minimum and maximum values.
• Susceptibility. Aspect of a piece of equ ipment that describes its inability to function acceptably when subjected to unwanted electromagnetic energy.
• Susceptibility Level. Level where the effects of interference from electromagnetic energy become apparent.
• Timely Manner. The necessary period for a system to reconfigure safely after a disruption.
Note: Timely recovery has been introduced to account for this period. The meaning of ‘in a timely manner’ depends on the function performed by the system being evaluated, the specific system design, the interactions between the system and the flightcrew, and the phase of flight. The definition of ‘in a timely manner’ should be determined for each system and for the specific functions performed by the system.
The applicable definition may be in cluded in the HIRF safety assessment.
• 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 t o the external HIRF field strength, as a function of frequency.
• 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.
6 BACKGROUND Electrical and electronic systems installed in aircraft may exhibit performance degradation when exposed to a HIRF environment. These systems perform functions whose failure may prevent the continued safe flight and landing of the aircraft or cause an adverse operating condition.
6.1 HIRF Environment.
The electromagnetic HIRF environment is created 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 ARP5583A or EUROCAE ED-107A, provides a detailed description of the derivation of these HIRF environments.
6.2 Aircraft Protection.
Concerns over the need to protect aircraft electrical and electronic systems ha ve increased substantially because of:
• Greater dependence on electrical and electronic systems performing functions required for continued safe flight and landing of an aircraft;
• Reduced electromagnetic shielding afforded by some composite materials used in aircraft designs;
• Increased susceptibility of electrical and electronic systems to HIRF because of increased data bus and processor operating speeds, higher density integrated circuits, and greater sensitivities of electronic equipment;
• Expanded frequency usage, especially above 1 GHz;
• Increased severity of the HIRF environment because of an increase in the number of RF transmitters; and
• Adverse effects experienced by some aircraft when exposed to HIRF.
7 STEPS FOR SHOWING COMPLIANCE
7.1 HIRF Certification Program.
The following activities should be elements of a proper HIRF certification program.
You should:
• Identify the systems to be assessed;
• Perform a HIRF safety assessment;
• Establish the applicable aircraft external HIRF environment;
• Establish the test environment for install ed systems;
• Apply HIRF compliance verification method;
• Verify HIRF protection effectiveness; and
• Take corrective measures (if needed).
Note: The user’s guide, SAE ARP5583A or EUROCAE ED-107A, contains more detailed information on HIRF certification compliance.
7.2 Identify the Systems to be Assessed .
7.2.1 You should identify the aircraft systems that will need a HIRF safety assessment. You should define the elements of the system performing a function, considering redundant or backup equipment that makes up t he system. The process used for identifying these systems should be similar to the process for showing compliance with §§ 23.1309,
23.2510, 25.1309, 27.1309, and 29.1309, as applicable. You should assess the effects of a HIRF encounter to determine the degree to which the aircraft and its systems’ safety may be affected.
7.2.2 You should assess the operation of the aircraft systems separately and in combination with, or in relation to, other systems. This assessment should cover all:
• Normal aircraft operating modes, stages of flight, and operating conditions;
• HIRF-related failure conditions and their subsequent effect on aircraft operations and the flightcrew; and
• System responses and any required flightcrew actions.
7.3 HIRF Safety Assessment.