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AMC 20-158A Aircraft electrical and electronic system high-intensity radiated fields (HIRF) protection

Available versions for ERULES-1963177438-19880

ED Decision 2022/001/R found in: AMC-20 Amdt 23 - Airworthiness of Products, Parts and Appliances (Jan 2022)

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AMC 20-158A Aircraft
electrical and electronic system high-intensity radiated fields (HIRF)
protection

ED Decision 2022/001/R

1.         PURPOSE

a.         This
AMC describes an acceptable means, but not the only means, for demonstrating
compliance with the applicable certification specifications (CSs) related to high-intensity
radiated fields (HIRF) protection (CS 23.1308, 25.1317, 27.1317, and
29.1317). Compliance with this AMC is not mandatory, and an applicant may
elect to use an alternative means of compliance. However, the alternative
means of compliance must meet the relevant requirements, ensure an equivalent
level of safety, and be approved by EASA on a product or ETSO article basis.

b.         The
modal verb ‘must’ is used to indicate which means are necessary to demonstrate
compliance with the applicable CSs by using this AMC. The modal verb ‘should’
is used when following the AMC to indicate that an action is recommended but
is not necessary to demonstrate compliance with the applicable CSs when using
this AMC.

**2.         SCOPE AND APPLICABILITY**

This AMC provides possible means to demonstrate compliance
with CS 23.1308/23.2520, 25.1317, 27.1317, and 29.1317 for the effects of
HIRFs. This AMC may be used by applicants for a new type certificate (TC) or a
change to an existing TC when the certification basis requires to address the
above-mentioned CSs.

Note: For CS-23 Amendment 5 and
higher, a new HIRF specification, i.e. CS 23.2520, which differs from the
previous CS 23.1308, is included. The associated AMC to CS 23.2520 are
published separately in the AMC & GM to CS-23, based on ASTM
F3061/F3061M-17 and F3236-17.This AMC could nevertheless be used as guidance
for demonstrating compliance with CS 23.2520.

**3.         DOCUMENT HISTORY**

This AMC supersedes[AMC
20-158](https://dxweb.easa.europa.eu/dx4/Topics/easaNewTopica32a34d9-db54-40b3-bf36-6435a2d2adca.docx), Aircraft Electrical and Electronic System
High-Intensity Radiated Fields (HIRF) Protection, dated 15 July 2015.

**4.         RELATED MATERIAL**

a.         European
Union Aviation Safety Agency (EASA) (in this document also referred to as ‘the
Agency’)

Certification Specifications:

1.         CS
23.1308, CS 25.1317, CS 27.1317, and CS 29.1317, High-intensity
Radiated Fields (HIRF)             Protection;

2.         CS
23.1309, CS 25.1309, CS 27.1309, and CS 29.1309, Equipment,
systems, and installations; and

3.         CS
23.1529, CS 25.1529, CS 27.1529, and CS 29.1529, Instructions
for Continued Airworthiness.

EASA Certification Specifications (CSs) and Acceptable Means
of Compliance (AMC) may be downloaded from the EASA website at [www.easa.europa.eu](http://www.easa.europa.eu).

b.         FAA
Advisory Circulars (ACs)

1.         AC
23.1309-1E, System Safety Analysis and Assessment for Part
23 Airplanes;

2.         AC
25.1309-1A, System Design and Analysis;

3.         AC-27-1B, Certification of Normal Category Rotorcraft;

4.         AC-29-2C, Certification of Transport Category Rotorcraft, or later
revisions;

5.         AC
20-158A, The Certification of Aircraft Electrical and
Electronic Systems for Operation in the High‑Intensity Radiated Fields (HIRF)   Environment.

Applicants can view and download copies from the web-based
FAA Regulatory and Guidance Library (RGL) at [www.airweb.faa.gov](http://www.airweb.faa.gov). On the RGL website,
the applicant should select ‘Advisory Circular’, then select ‘By Number’. ACs
are also available on the FAA website at [http://www.faa.gov/regulations\_policies/advisory\_circulars/](http://www.faa.gov/regulations_policies/advisory_circulars).

c.         European
Organisation for Civil Aviation Equipment (EUROCAE)

Copies of these documents can be requested 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;

2.         EUROCAE
ED-14G, Environmental Conditions and Test Procedures for
Airborne Equipment;

3.         EUROCAE
ED-79A, Guidelines for Development of Civil Aircraft and
Systems;

4.         EUROCAE
ED-234, User Guide Supplement to EUROCAE ED-14G.

EUROCAE documents may be purchased from:

European Organisation for Civil Aviation Equipment

9-23 rue Paul Lafargue

"Le Triangle" building

93200 Saint-Denis, France

Telephone: +33 1 49 46 19 65

(Email: eurocae@eurocae.net,
website: [www.eurocae.net](http://www.eurocae.net)

d.         Radio
Technical Commission for Aeronautics (RTCA)

RTCA/DO-160G, Environmental Conditions and
Test Procedures for Airborne Equipment. This document is technically
equivalent to EUROCAE ED-14G.

RTCA documents may be purchased from:

RTCA, Inc., 1150 18th Street NW, Suite 910, Washington D.C.
20036, USA

(Email: info@rtca.org,
website: [www.rtca.org](http://www.rtca.org)

e.         Society
of Automotive Engineers (SAE International)

1.         SAE
Aerospace Recommended Practice (ARP)5583A,Guide to
Certification of Aircraft in a High Intensity Radiated Field (HIRF)
Environment. SAE ARP 5583A and ED-107A are technically equivalent and
either document may serve as the ‘User’s Guide’ referred to in this AMC.

2.         SAE ARP
4754A, Guidelines For Development Of Civil Aircraft And
Systems, dated December 2010. This document is technically equivalent
to EUROCAE ED-79A.

3.         SAE ARP
4761, Guidelines and Methods for Conducting the Safety
Assessment Process on Civil Airborne Systems and Equipment, dated December
1996.

SAE International documents may be purchased from:

SAE Customer Service

400 Commonwealth Drive

Warrendale, PA

15096-0001, USA

Website: [http://www.sae.org](http://www.sae.org/)

**5.         BACKGROUND**

**a.         Aircraft protection.** The need 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.         the
reduced electromagnetic shielding afforded by some composite materials used in
aircraft designs;

3.         the
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.         the
increased severity of the HIRF environment because of an increase in the
number and radiated power of radio frequency (RF) transmitters; and

6.         the
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.

6.         APPROACHES
TO COMPLIANCE

**a.         General.** The following activities
should be elements of a proper HIRF certification programme. Adherence to the
sequence shown is not necessary. More detailed information on HIRF
certification compliance is provided in the User’s Guide (ED-107A).

The applicantshould:

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;

5.         verify the
effectiveness of the HIRF protection; and

6.         take
corrective measures (if needed).

More detailed information on these activities is proposed in Sections7
and 8 of this AMC.

**b.         Identify the systems to be assessed**

**1.         General.** The applicant should
identify the aircraft systems requiring a HIRF safety assessment. The
applicant should define the elements of the system performing a function,
considering similar and/or dissimilar redundant channels that make up the
system. The process used for identifying these systems should be similar to
the process for demonstrating compliance with CS 23.1309, 25.1309, 27.1309,
and 29.1309, as applicable. These paragraphs 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 safety of the aircraft and its systems 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, phases of flight, and operating conditions;

(b)      all HIRF-related
failure conditions and their subsequent effects on aircraft operations and the
flightcrew; and

**2.         HIRF 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 (HCL) for
the appropriate HIRF requirements. The failure condition classifications and
terms used in this AMC are similar to those used in AC 23.1309-1E, AMC
25.1309, 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 requirements.
Based on the safety classification of the failure condition classification by
the safety assessment, the systems should be assigned appropriate HCLs, as
shown in Table 1. The HIRF safety assessment should consider the common-cause
effects of HIRF, particularly for highly integrated systems and systems with
redundant elements. The HIRF safety assessment determines the consequences of
failures for the aircraft functions that are performed by the system. The
system HCL classification assigned to the systems and functions can be
different from the development assurance level (ED-79A) or the design assurance
level (ED-80) assigned for equipment redundancy, software, and airborne
electronic hardware (AEH). This is because HIRF is an environment that can
cause common-cause effects. The term ‘DAL’ should not be used to describe the
system HCL because of the potential differences in assigned classifications for
software, AEH, and equipment redundancy. The HIRF safety assessment must
include all electrical and electronic equipment, components and electrical
interconnections, assuming that they are potentially affected by HIRF. It is
not appropriate to use the HIRF immunity data for electrical and electronic
equipment, components and electrical interconnections as information input for
the HIRF safety assessment. This information should only be used in the next
phase, to show compliance with the applicable subpart of the HIRF requirements,
after the required HCL for the system is defined by the HIRF safety
assessment. The HIRF safety assessment must have input and be coordinated
between the safety specialist, the system specialist, and the HIRF/lightning
specialist. This process may vary from applicant to applicant. Further
guidance on performing the safety assessment can be found in AC 23.1309-1E,
AMC 25.1309, AC-27-1B, AC-29-2C, SAE ARP 4754A/EUROCAE ED-79A, SAE ARP 4761,
and ARP 5583A/EUROCAE ED‑107A.

Note: Considering that HIRF and
lightning environments may have similar effects on electro‑electronic systems
(disturbing electrical signals, causing upsets or damage to circuits), and
that the applicable certification specifications are similarly structured, in
many cases the system HCL and corresponding LCL (see[AMC 20-136A](#_DxCrossRefBm1926189325)) should be the same.

Table 1: HIRF most severe failure conditions of the
function and system HIRF certification levels

<table border="0" cellpadding="0" cellspacing="0" width="624">
<tr>
<td rowspan="4" valign="bottom" width="293">
HIRF
 REQUIREMENTS EXCERPTS FROM CS 23.1308, CS 25.1317, CS 27.1317, AND CS
 29.1317
</td>
<td valign="bottom" width="9">
</td>
<td rowspan="4" valign="bottom" width="151">
MOST SEVERE FAILURE CONDITION
 OF THE FUNCTION
</td>
<td valign="bottom" width="28">
</td>
<td rowspan="4" valign="bottom" width="142">
SYSTEM HIRF
CERTIFICATION LEVEL (HCL)
</td>
</tr>
<tr>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="28">
</td>
</tr>
<tr>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="28">
</td>
</tr>
<tr>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="28">
</td>
</tr>
<tr>
<td valign="bottom" width="293">
</td>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="151">
</td>
<td valign="bottom" width="28">
</td>
<td valign="bottom" width="142">
</td>
</tr>
<tr>
<td rowspan="3" valign="bottom" width="293">
(a) Each electrical and electronic system that performs
 a function whose failure would prevent the continued safe flight and landing
 of the aircraft.
</td>
<td valign="bottom" width="9">
</td>
<td rowspan="4" valign="bottom" width="151">
Catastrophic
</td>
<td valign="bottom" width="28">
</td>
<td rowspan="4" valign="bottom" width="142">
A
</td>
</tr>
<tr>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="28">
</td>
</tr>
<tr>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="28">
</td>
</tr>
<tr>
<td valign="bottom" width="293">
</td>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="28">
</td>
</tr>
<tr>
<td valign="bottom" width="293">
</td>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="151">
</td>
<td valign="bottom" width="28">
</td>
<td valign="bottom" width="142">
</td>
</tr>
<tr>
<td rowspan="5" valign="bottom" width="293">
(b) Each electrical and electronic system that
 performs a function whose failure would significantly reduce the capability
 of the aircraft or the ability of the flight crew to respond to an adverse
 operating condition.
</td>
<td valign="bottom" width="9">
</td>
<td rowspan="6" valign="bottom" width="151">
Hazardous
</td>
<td valign="bottom" width="28">
</td>
<td rowspan="6" valign="bottom" width="142">
B
</td>
</tr>
<tr>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="28">
</td>
</tr>
<tr>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="28">
</td>
</tr>
<tr>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="28">
</td>
</tr>
<tr>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="28">
</td>
</tr>
<tr>
<td valign="bottom" width="293">
</td>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="28">
</td>
</tr>
<tr>
<td valign="bottom" width="293">
</td>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="151">
</td>
<td valign="bottom" width="28">
</td>
<td valign="bottom" width="142">
</td>
</tr>
<tr>
<td valign="bottom" width="293">
</td>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="151">
</td>
<td valign="bottom" width="28">
</td>
<td valign="bottom" width="142">
</td>
</tr>
<tr>
<td rowspan="4" valign="bottom" width="293">
(c) Each electrical and electronic system that
 performs a function whose failure would reduce the capability of the
 aircraft or the ability of the flight crew to respond to an adverse
 operating condition.
</td>
<td valign="bottom" width="9">
</td>
<td rowspan="4" valign="bottom" width="151">
Major
</td>
<td valign="bottom" width="28">
</td>
<td rowspan="4" valign="bottom" width="142">
C
</td>
</tr>
<tr>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="28">
</td>
</tr>
<tr>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="28">
</td>
</tr>
<tr>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="28">
</td>
</tr>
<tr>
<td valign="bottom" width="293">
</td>
<td valign="bottom" width="9">
</td>
<td valign="bottom" width="151">
</td>
<td valign="bottom" width="28">
</td>
<td valign="bottom" width="142">
</td>
</tr>
</table>

**3.         Level A systems.** The
specifications in CS 23.1308(a), 25.1317(a), 27.1317(a), and 29.1317(a)
address adverse effects on the aircraft functions and systems that perform
functions whose failure would prevent the continued safe flight and landing of
the aircraft. When demonstrating compliance with CS 23.1308(a), 25.1317(a),
27.1317(a), and 29.1317(a), the electrical and electronic system is the one
required to perform the function whose failure would prevent continued safe
flight and landing. This electrical and electronic system must also
automatically recover normal operation of the Level A functions in a timely
manner to comply with CS 23.1308(a)(2), 25.1317(a)(2), 27.1317(a)(2), and
29.1317(a)(2). If all equipment and components of the system required for the
normal operation of the Level A functions are not susceptible when complying
with paragraphs (a)(1), (a)(2) and (a)(3), then it is acceptable that the
equipment and components required only for non-normal situations do not show
compliance with the requirements of paragraph (a). In this case, it is
considered acceptable that the equipment and components of the system required
only for non-normal situations show compliance at least with the requirements
of paragraph (b).

**4.         Level B or Level C systems.** The
specifications in CS 23.1308(b)(c), 25.1317(b)(c), 27.1317(b)(c), and
29.1317(b)(c) address adverse effects on systems that perform functions whose
failure would reduce the capability of the [aircraft](https://www.law.cornell.edu/cfr/text/14/25.1317) or
the ability of the flight crew to respond to an adverse operating condition
when all equipment, components and electrical interconnections of the Level B
or Level C system are exposed to HIRF test Level 1 or 2, or 3 respectively.

If some of the electrical and electronic equipment of a Level
A system perform Level B or Level C functions, and effects on these equipment
items are noted when the system is submitted to Level A HIRF environments,
these effects should be reassessed when the system is submitted to HIRF test Level
1 or 2, or 3 respectively.

**5.         Failure conditions.** The HIRF
safety assessment should consider all potential adverse effects due to system
failures, malfunctions, or misleading information. The HIRF safety assessment
may show that some systems have different failure conditions in different
phases of flight; therefore, the system HCL corresponds to the most severe
failure condition. 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 CS 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

<table border="1" cellpadding="0" cellspacing="0">
<tr>
<td rowspan="2" valign="top" width="187">
FREQUENCY
</td>
<td colspan="2" valign="top" width="378">
FIELD
 STRENGTH (V/m)
</td>
</tr>
<tr>
<td valign="top" width="204">
PEAK
</td>
<td valign="top" width="174">
AVERAGE
</td>
</tr>
<tr>
<td valign="top" width="187">
10 kHz–2 MHz
</td>
<td valign="top" width="204">
50
</td>
<td valign="top" width="174">
50
</td>
</tr>
<tr>
<td valign="top" width="187">
2–30
 MHz
</td>
<td valign="top" width="204">
100
</td>
<td valign="top" width="174">
100
</td>
</tr>
<tr>
<td valign="top" width="187">
30–100 MHz
</td>
<td valign="top" width="204">
50
</td>
<td valign="top" width="174">
50
</td>
</tr>
<tr>
<td valign="top" width="187">
100–400
 MHz
</td>
<td valign="top" width="204">
100
</td>
<td valign="top" width="174">
100
</td>
</tr>
<tr>
<td valign="top" width="187">
400–700 MHz
</td>
<td valign="top" width="204">
700
</td>
<td valign="top" width="174">
50
</td>
</tr>
<tr>
<td valign="top" width="187">
700
 MHz–1 GHz
</td>
<td valign="top" width="204">
700
</td>
<td valign="top" width="174">
100
</td>
</tr>
<tr>
<td valign="top" width="187">
1–2 GHz
</td>
<td valign="top" width="204">
2 000
</td>
<td valign="top" width="174">
200
</td>
</tr>
<tr>
<td valign="top" width="187">
2–6
 GHz
</td>
<td valign="top" width="204">
3 000
</td>
<td valign="top" width="174">
200
</td>
</tr>
<tr>
<td valign="top" width="187">
6–8 GHz
</td>
<td valign="top" width="204">
1 000
</td>
<td valign="top" width="174">
200
</td>
</tr>
<tr>
<td valign="top" width="187">
8–12
 GHz
</td>
<td valign="top" width="204">
3 000
</td>
<td valign="top" width="174">
300
</td>
</tr>
<tr>
<td valign="top" width="187">
12–18 GHz
</td>
<td valign="top" width="204">
2 000
</td>
<td valign="top" width="174">
200
</td>
</tr>
<tr>
<td valign="top" width="187">
18–40
 GHz
</td>
<td valign="top" width="204">
600
</td>
<td valign="top" width="174">
200
</td>
</tr>
<tr>
<td colspan="3" valign="top" width="565">
In this table, the higher field strength applies at the
 frequency band edges.
</td>
</tr>
</table>

Table 3: HIRF Environment II

<table border="1" cellpadding="0" cellspacing="0">
<tr>
<td rowspan="2" valign="top" width="187">
FREQUENCY
</td>
<td colspan="2" valign="top" width="378">
FIELD
 STRENGTH (V/m)
</td>
</tr>
<tr>
<td valign="top" width="204">
PEAK
</td>
<td valign="top" width="174">
AVERAGE
</td>
</tr>
<tr>
<td valign="top" width="187">
10–500 kHz
</td>
<td valign="top" width="204">
20
</td>
<td valign="top" width="174">
20
</td>
</tr>
<tr>
<td valign="top" width="187">
500
 kHz–2 MHz
</td>
<td valign="top" width="204">
30
</td>
<td valign="top" width="174">
30
</td>
</tr>
<tr>
<td valign="top" width="187">
2–30 MHz
</td>
<td valign="top" width="204">
100
</td>
<td valign="top" width="174">
100
</td>
</tr>
<tr>
<td valign="top" width="187">
30–100
 MHz
</td>
<td valign="top" width="204">
10
</td>
<td valign="top" width="174">
10
</td>
</tr>
<tr>
<td valign="top" width="187">
100–200 MHz
</td>
<td valign="top" width="204">
30
</td>
<td valign="top" width="174">
10
</td>
</tr>
<tr>
<td valign="top" width="187">
200–400
 MHz
</td>
<td valign="top" width="204">
10
</td>
<td valign="top" width="174">
10
</td>
</tr>
<tr>
<td valign="top" width="187">
400 MHz–1 GHz
</td>
<td valign="top" width="204">
700
</td>
<td valign="top" width="174">
40
</td>
</tr>
<tr>
<td valign="top" width="187">
1–2
 GHz
</td>
<td valign="top" width="204">
1 300
</td>
<td valign="top" width="174">
160
</td>
</tr>
<tr>
<td valign="top" width="187">
2–4 GHz
</td>
<td valign="top" width="204">
3 000
</td>
<td valign="top" width="174">
120
</td>
</tr>
<tr>
<td valign="top" width="187">
4–6
 GHz
</td>
<td valign="top" width="204">
3 000
</td>
<td valign="top" width="174">
160
</td>
</tr>
<tr>
<td valign="top" width="187">
6–8 GHz
</td>
<td valign="top" width="204">
400
</td>
<td valign="top" width="174">
170
</td>
</tr>
<tr>
<td valign="top" width="187">
8–12
 GHz
</td>
<td valign="top" width="204">
1 230
</td>
<td valign="top" width="174">
230
</td>
</tr>
<tr>
<td valign="top" width="187">
12–18 GHz
</td>
<td valign="top" width="204">
730
</td>
<td valign="top" width="174">
190
</td>
</tr>
<tr>
<td valign="top" width="187">
18–40
 GHz
</td>
<td valign="top" width="204">
600
</td>
<td valign="top" width="174">
150
</td>
</tr>
<tr>
<td colspan="3" valign="top" width="565">
In this table, the higher field strength applies at the
 frequency band edges.
</td>
</tr>
</table>

Table 4: HIRF
Environment III

<table border="1" cellpadding="0" cellspacing="0">
<tr>
<td rowspan="2" valign="top" width="187">
FREQUENCY
</td>
<td colspan="2" valign="top" width="390">
FIELD
 STRENGTH (V/m)
</td>
</tr>
<tr>
<td valign="top" width="204">
PEAK
</td>
<td valign="top" width="186">
AVERAGE
</td>
</tr>
<tr>
<td valign="top" width="187">
10–100 kHz
</td>
<td valign="top" width="204">
150
</td>
<td valign="top" width="186">
150
</td>
</tr>
<tr>
<td valign="top" width="187">
100
 kHz–400 MHz
</td>
<td valign="top" width="204">
200
</td>
<td valign="top" width="186">
200
</td>
</tr>
<tr>
<td valign="top" width="187">
400–700 MHz
</td>
<td valign="top" width="204">
730
</td>
<td valign="top" width="186">
200
</td>
</tr>
<tr>
<td valign="top" width="187">
700
 MHz–1 GHz
</td>
<td valign="top" width="204">
1 400
</td>
<td valign="top" width="186">
240
</td>
</tr>
<tr>
<td valign="top" width="187">
1–2 GHz
</td>
<td valign="top" width="204">
5 000
</td>
<td valign="top" width="186">
250
</td>
</tr>
<tr>
<td valign="top" width="187">
2–4
 GHz
</td>
<td valign="top" width="204">
6 000
</td>
<td valign="top" width="186">
490
</td>
</tr>
<tr>
<td valign="top" width="187">
4–6 GHz
</td>
<td valign="top" width="204">
7 200
</td>
<td valign="top" width="186">
400
</td>
</tr>
<tr>
<td valign="top" width="187">
6–8
 GHz
</td>
<td valign="top" width="204">
1 100
</td>
<td valign="top" width="186">
170
</td>
</tr>
<tr>
<td valign="top" width="187">
8–12 GHz
</td>
<td valign="top" width="204">
5 000
</td>
<td valign="top" width="186">
330
</td>
</tr>
<tr>
<td valign="top" width="187">
12–18
 GHz
</td>
<td valign="top" width="204">
2 000
</td>
<td valign="top" width="186">
330
</td>
</tr>
<tr>
<td valign="top" width="187">
18–40 GHz
</td>
<td valign="top" width="204">
1 000
</td>
<td valign="top" width="186">
420
</td>
</tr>
<tr>
<td colspan="3" valign="top" width="577">
In this table, the higher field strength applies at the
 frequency band edges.
</td>
</tr>
</table>

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 of external HIRF Environment I, II, or III, as defined in CS-23
Appendix K, in CS‑25 Appendix R, in CS-27 Appendix D, and in CS-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 Section 8 of this AMC.

**3.         Level B systems.** The internal RF
environments for Level B systems are defined in CS-23 Appendix K, in CS-25
Appendix R, in CS-27 Appendix D, and in CS-29 Appendix E, as applicable, as
equipment HIRF test Levels 1 or 2. The steps for showing Level B HIRF
compliance are presented in Section 9 of this AMC.

**4.         Level C systems.** The internal RF
environment for Level C systems is defined in CS-23 Appendix K, in CS‑25
Appendix R, in CS-27 Appendix D, and in CS-29 Appendix E, as applicable, as
equipment HIRF test Level 3. The steps for showing Level C HIRF compliance are
also presented in Section 9 of this AMC.

e.         Apply
the appropriate method of HIRF compliance verification

**1.         General.** Table 5 summarises the
relationship between the aircraft performance requirements in the HIRF requirements
(paragraphs (a), (b) and (c)), and the HIRF environments and test levels.

**2.         Pass/fail criteria.** Establish
specific HIRF compliance pass/fail criteria for each system corresponding to
the applicable HIRF requirements performance criteria. The definitions of
‘normal operation’ and ‘automatically recover’ in paragraph 5 of this AMCare
provided in the context of CS23.1308(a)(2), 25.1317(a)(2), 27.1317(a)(2), and
29.1317(a)(2). These pass/fail criteria should be presented to the Agency for
approval. The means for monitoring system performance relative to these
criteria should be established by the applicant and approved by the Agency.
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 channel performing the
same function.

Table 5: Summary
of the HIRF certification requirements

<table border="0" cellpadding="0" cellspacing="3" width="624">
<tr>
<td valign="top" width="194">
HIRF FAILURE
 CONDITION FROM
CSs 23.1308, 25.1317,
 27.1317, AND 29.1317
</td>
<td valign="top" width="158">
PERFORMANCE
 CRITERIA
</td>
<td valign="top" width="148">
ITEM THE ENVIRONMEN OR TEST
LEVEL APPLIES TO
</td>
<td valign="top" width="109">
HIRF ENVIRONMENT OR TEST LEVEL
</td>
</tr>
<tr>
<td valign="top" width="194">
Each electrical and electronic system that
 performs a function whose failure would prevent the continued safe flight
 and landing of the aircraft/rotorcraft must be designed and installed so
 that:
</td>
<td width="158">
Each function is not adversely
 affected during or after the time…
</td>
<td width="148">
…the aircraft …
</td>
<td width="109">
…is exposed to HIRF Environment
 I.
</td>
</tr>
<tr>
<td rowspan="3" valign="top" width="194">
</td>
<td width="158">
Each electrical and electronic
 system automatically recovers normal operation of that function, in a timely
 manner after…
</td>
<td width="148">
…the aircraft…
</td>
<td width="109">
…is exposed to HIRF Environment
 I, unless this conflicts with other operational or functional requirements
 of that system.
</td>
</tr>
<tr>
<td width="158">
Each electrical and electronic
 system is not adversely affected during or after…
</td>
<td width="148">
…the aircraft…
</td>
<td width="109">
…is exposed to HIRF Environment
 II.
</td>
</tr>
<tr>
<td width="158">
Each function required during
 operation under visual flight rules (VFR) is not adversely affected during
or after…
</td>
<td width="148">
…the rotorcraft…
</td>
<td width="109">
…is exposed to HIRF Environment
 III 
 (CS 27 and CS 29 only).
</td>
</tr>
<tr>
<td valign="top" width="194">
Each electrical and electronic system that
 performs a function whose failure would significantly reduce the capability
 of the aircraft/rotorcraft or the ability of the flight crew to respond to
 an adverse operating condition must be designed and installed so that:
</td>
<td width="158">
The system is not adversely
 affected when…
</td>
<td width="148">
…the equipment providing these
 functions…
</td>
<td width="109">
…is exposed to equipment HIRF
 test Level 1 or 2.
</td>
</tr>
<tr>
<td valign="top" width="194">
Each electrical and electronic system that
 performs afunction whose failure would reduce the capability of the aircraft/rotorcraft
 or the ability of the flight crew to respond to an adverse operating
 condition must be designed and installed so that:
</td>
<td valign="top" width="158">
The system is not adversely
 affected when…
</td>
<td valign="top" width="148">
…the equipment providing these
 functions…
</td>
<td valign="top" width="109">
…is exposed to equipment HIRF
 test Level 3.
</td>
</tr>
</table>

f.          Verify
compliance with the applicable requirements

1.         The
applicant should demonstratethat the systems comply with the applicable
specifications of CS23.1308, 25.1317, 27.1317, and 29.1317.

2.         The applicantshould
show that the RF currents on system and equipment wire bundles and the RF
fields on the system, created by the HIRF environment, are lower than the
equipment or system HIRF qualification test levels.

3.         Verification
may be accomplished by tests, analyses, or by demonstrating similarity to
previously certified aircraft and systems. The certification process for Level
A systems is contained in Section 7. The certification process for Level
B and Level C systems is contained in Section 8.

4.         Margins
are not required if HIRF compliance is based on tests of the specific aircraft
model and system that undergo certification. Margins are also not required if
HIRF compliance is based on analysis or similarity if the process validation
is robust and the data well substantiated. Where data has limited
substantiation, a margin may be required, depending on the available
justifications. When a margin is required, the applicant should include a
justification for the selected margin in the HIRF compliance plan, as
discussed in Section 6(a).

5.         The
applicant should submit theircompliance plan in the early stages of the certification
programme to theAgency for review (see the details in Section 6(a)).
Experience shows that, particularly with aircraft using new technology or
those that have complex systems, early agreement on the compliance plan
benefits both the applicant and the Agency. The plan should define acceptable
ways to resolve critical issues during the certification process. Analyses and
test results during the certification process may warrant modifications to the
design or verification methods. When significant changes are necessary, the
certification plan should be updated accordingly.

g.         Take
corrective measures (if needed)

If tests and analyses show that the system did not meet the
pass/fail criteria, the applicant should review the aircraft, installation or
system design, and improve the protection against HIRF.

Figure 1: Routes to HIRF compliance — Level A systems

![Aviation.Bot AI suggestion, not from EASA source: This image is a flowchart illustrating the various routes and steps required to demonstrate High-Intensity Radiated Fields (HIRF) compliance for Level A systems in aircraft, encompassing both aircraft-level and system-level verification processes.

Detailed Description:
The image displays a flowchart composed of rectangular boxes (representing processes or steps), diamond shapes (representing decision points), and arrows (indicating flow direction and relationships). All steps are numbered in parentheses, corresponding to step numbers described in Section 7 of the AMC.

The flowchart begins at the top left with a rectangular box labeled "System safety assessment (1)". An arrow, labeled "Level A System", points horizontally from this box to a central rectangular box labeled "Define aircraft and system HIRF protection (2)".

From "Define aircraft and system HIRF protection (2)", the process branches into two main verification paths, visually separated by shaded areas and dashed borders:

1.  **Aircraft-level verification:** This section is a light gray shaded area enclosed by a dashed line, labeled "Aircraft-level verification" at its top left. An arrow points from "Define aircraft and system HIRF protection (2)" to a diamond-shaped decision box within this section, labeled "Select aircraft assessment (7)".
    *   From "Select aircraft assessment (7)", three paths emerge:
        *   An arrow labeled "Aircraft test" points downwards to a diamond-shaped decision box labeled "Aircraft test decision (8)".
        *   An arrow labeled "Level A display only" points horizontally right to a rectangular box labeled "Generic transfer functions / attenuation (11)".
        *   An arrow labeled "similarity" points downwards to a rectangular box labeled "Aircraft similarity assessment (12)".
    *   From "Aircraft test decision (8)", two paths emerge:
        *   An arrow points downwards to a rectangular box labeled "Aircraft high-level tests (9)".
        *   An arrow points downwards to a rectangular box labeled "Aircraft low-level coupling tests (10)". Below this box, the text "See Figure 2" is present.

2.  **System-level verification:** This section is a light gray shaded area enclosed by a dashed line, labeled "System-level verification" at its top right. An arrow points from "Define aircraft and system HIRF protection (2)" to a diamond-shaped decision box within this section, labeled "Select system assessment (3)".
    *   From "Select system assessment (3)", two paths emerge:
        *   An arrow labeled "Test" points downwards to a rectangular box labeled "Equipment test (4)".
        *   An arrow labeled "Similarity" points horizontally right to a rectangular box labeled "System similarity assessment (6)".
    *   An arrow points downwards from "Equipment test (4)" to a rectangular box labeled "Integrated system test (5)".
    *   An arrow points downwards from "Integrated system test (5)" to "System similarity assessment (6)".

All paths from both verification sections converge at a central diamond-shaped decision box labeled "Assess the immunity (13)", located at the bottom center of the flowchart. Arrows point to "Assess the immunity (13)" from:
*   "Aircraft high-level tests (9)"
*   "Aircraft low-level coupling tests (10)"
*   "Generic transfer functions / attenuation (11)"
*   "Aircraft similarity assessment (12)"
*   "System similarity assessment (6)"

From "Assess the immunity (13)", two outcomes are possible:
*   An arrow labeled "Acceptable" points downwards to a rectangular box labeled "HIRF protection compliance (15)".
*   An arrow labeled "Unacceptable" points horizontally right to a rectangular box labeled "Corrective measures (14)".

An arrow points from "Corrective measures (14)" back upwards to "Define aircraft and system HIRF protection (2)", indicating a feedback loop for re-evaluation.

Contextual Linkage:
The flowchart outlines a structured process for demonstrating HIRF compliance for Level A systems. It starts with a system safety assessment (1) to classify the system as Level A, which then leads to defining the HIRF protection strategy (2). The process then branches into two parallel or sequential verification approaches: aircraft-level verification and system-level verification. Both paths involve various assessment methods, including testing (e.g., Aircraft high-level tests (9), Equipment test (4)) and similarity assessments (e.g., Aircraft similarity assessment (12), System similarity assessment (6)). The "Aircraft low-level coupling tests (10)" explicitly references "Figure 2", indicating a related diagram for that specific test. All verification paths ultimately lead to an assessment of immunity (13). If the immunity is deemed "Unacceptable", corrective measures (14) are required, leading back to redefine protection (2). If "Acceptable", the process concludes with "HIRF protection compliance (15)".](file_tNNDI2wQkpg/image072.png)

(n) = Step number as described inSection 7 of this AMC

Figure 2: Aircraft low-level coupling tests — Level A
systems

![Aviation.Bot AI suggestion, not from EASA source: This image is a flowchart illustrating the process for conducting aircraft low-level coupling tests, specifically for Level A systems, detailing various test methods and their associated frequency ranges.

Detailed Description:
The image displays a flowchart with a central, large, light gray rectangular box titled "Aircraft low-level coupling tests (10)". This box encloses four smaller, white rectangular boxes, each representing a specific test or analysis step.

At the top of the flowchart, a white circular node labeled "From Figure 1 Step 10" serves as the entry point. A solid black arrow extends vertically downwards from this node, pointing towards the top edge of the large gray box.

Inside the gray box, the incoming arrow branches into three distinct vertical paths, each leading to a different initial test or analysis:
1.  **Left Path:** An arrow points downwards to a white rectangular box labeled "Aircraft skin current analysis (10a)". A horizontal text label, "10 kHz to the 1st Airframe Resonant Frequency", is positioned to the left of this arrow segment, indicating the frequency range for this path. From "Aircraft skin current analysis (10a)", another solid black arrow points vertically downwards to a second white rectangular box labeled "Low-level direct-drive test (10b)".
2.  **Middle Path:** An arrow points downwards directly to a white rectangular box labeled "Low-level swept-current test (10c)". A horizontal text label, "500 kHz to 400 MHz", is positioned to the right of this arrow segment, indicating the frequency range for this path.
3.  **Right Path:** An arrow points downwards directly to a white rectangular box labeled "Low-level swept-field test (10d)". A horizontal text label, "100 MHz to 18 GHz", is positioned to the left of this arrow segment, indicating the frequency range for this path.

At the bottom of the flowchart, a white circular node labeled "Back to Figure 1 Step 13" serves as the exit point. Solid black arrows converge on this node from the bottom of the three lowest test boxes:
*   An arrow from "Low-level direct-drive test (10b)" points downwards, then turns right to connect to the "Back to Figure 1 Step 13" node.
*   An arrow from "Low-level swept-current test (10c)" points directly downwards to connect to the "Back to Figure 1 Step 13" node.
*   An arrow from "Low-level swept-field test (10d)" points downwards, then turns left to connect to the "Back to Figure 1 Step 13" node.

Below the flowchart, a small text annotation reads: "(n) = Step number as described in Section 7 of this AMC".

Contextual Linkage:
The flowchart visually represents a segment of a larger compliance process for Level A systems, specifically detailing "Aircraft low-level coupling tests (10)". The process begins by transitioning from "Step 10" of "Figure 1" and concludes by returning to "Step 13" of "Figure 1". The diagram outlines three distinct testing methodologies—Aircraft skin current analysis/Low-level direct-drive test, Low-level swept-current test, and Low-level swept-field test—each applicable to specific radio frequency (RF) ranges, indicating a frequency-dependent approach to HIRF coupling assessment. The numerical identifiers (10a, 10b, 10c, 10d) within the test boxes correspond to specific steps described in Section 7 of the associated AMC.

Mermaid Diagram:
"mermaid
graph TD
    subgraph "Aircraft low-level coupling tests (10)"
        B["Aircraft skin current analysis (10a)"]
        C["Low-level direct-drive test (10b)"]
        D["Low-level swept-current test (10c)"]
        E["Low-level swept-field test (10d)"]
    end

A(("From Figure 1 Step 10")) --> |"10 kHz to the 1st Airframe Resonant Frequency"| B
    A --> |"500 kHz to 400 MHz"| D
    A --> |"100 MHz to 18 GHz"| E

B --> C
    C --> F(("Back to Figure 1 Step 13"))
    D --> F
    E --> F
"](file_tNNDI2wQkpg/image073.png)

(n) = Step number as described inSection 7 of this AMC

7.         STEPS
TO DEMONSTRATE ‘LEVEL A’ SYSTEM HIRF COMPLIANCE

Figures 1 and 2 illustrate a process that the applicant can
use to demonstrate that their Level A system complies with CS23.1308(a),
25.1317(a), 27.1317(a), and 29.1317(a).

a.         Step
1 — HIRF safety assessment

1.         The
applicant should determine the system failure condition classification for the
systems to be certified on their aircraft, using a system safety assessment as
discussed in Section 6(b)(2). For systems classified with catastrophic failure
conditions (Level A systems), the applicant should follow compliance steps 2
to 15 listed below, as appropriate. These compliance steps are also depicted
in Figures 1 and 2 of this AMC,and are not necessarily accomplished
sequentially. Applicants for systems classified with hazardous or major
failure conditions (HIRF certification Level B and Level C systems) should
follow the compliance steps outlined in Section 8 of this AMC.

2.         The system
defined for paragraph (a) of CS 23.1308, 25.1317, 27.1317, and 29.1317 is not
required to include:

(a)       equipment,
components and electrical interconnections required only for non-normal
situations; or

(b)       equipment,
components and electrical interconnections required only for dispatching under
master minimum equipment lists (MMELs) (when operational suitability data (OSD)
is applicable).

3.         Some
systems include mechanical, hydraulic, and/or pneumatic channels as well as
electrical and electronic channel(s) to perform functions whose failure would
prevent continued safe flight and landing. The HIRF safety assessment for CS
23.1308(a), 25.1317(a), 27.1317(a), and 29.1317(a) only applies to functions
performed by electrical and electronic systems. The HIRF safety assessment
should consider electrical or electronic failures that would adversely affect
the function of the mechanical, hydraulic, and/or pneumatic channel(s). If
electrical or electronic equipment and components, as well as electrical
interconnections are used to assist, augment, or monitor for control loop
feedback, the mechanical, hydraulic, and/or pneumatic channels in performing
the normal operation of the functions with failures that would prevent
continued safe flight and landing, then the electrical and electronic
channel(s) must comply with CS 23.1308(a), 25.1317(a), 27.1317(a), and
29.1317(a).

4.         CS
23.1308(a), 25.1317(a), 27.1317(a), and 29.1317(a) do not require the
applicant to assume pre‑existing failure conditions when classifying the
functional failure conditions and the scope of Level A systems. The applicant
should consider total or partial loss of the systems and malfunctions of the
systems, including hazardously misleading information presented to the flight
crew during and after the aircraft is exposed to HIRF.

5.         CS
23.1308(a)(2), 25.1317(a)(2), 27.1317(a)(2), and 29.1317(a)(2) require that
Level A systems automatically recover normal operation of the Level A
functions in a timely manner after exposure to HIRF Environment I. Automatic
recovery applies to all redundant active channels of the Level A system
required for normal operation unless its recovery conflicts with other
operational or functional requirements of the system. The exception for
automatic recovery conflicts must be based on aircraft operational or
functional requirements independent of HIRF exposure. The exception should not
be a mitigation for Level A system effects observed after exposure to HIRF
Environment I.

6.         [Appendix 3](#_DxCrossRefBm1926189331)Examples of
HIRF safety assessment considerations — Level A systemsprovides
examples of systems’ scope based on the guidance above.

b.         Step
2 — Define aircraft and system HIRF protection. The applicant should
define the HIRF protection features to be incorporated into the aircraft and
system designs, based on the HIRF environments that are applicable to their
aircraft and its Level A systems. Equipment, system, and aircraft HIRF
protection design may occur before aircraft-level tests are performed, and
before the actual internal HIRF environment is determined. Therefore, the
equipment, system and aircraft HIRF protection design should be based on an
estimate of the expected internal HIRF environment. The applicant should
consider all aircraft configurations that may affect HIRF protection, such as
open landing gear doors (see Step 7).

c.         Step
3 — System assessment decision. The applicant should determine whether
to perform integrated system HIRF tests on the Level A system, or to base the
system verification on previous integrated system HIRF tests performed on a
similar system. Aircraft and system tests and assessments need not be
performed for HIRF environments above 18 GHz if data and design analysis show
the integrated system test results (see Step 5) satisfy the pass/fail criteria
from 12 GHz to 18 GHz, and the systems have no circuits that operate in the 18
GHz to 40 GHz frequency range.

d.         Step
4 — Equipment test

1.         Radiated
and conducted RF susceptibility laboratory tests of RTCA/DO-160G/EUROCAE
ED-14G (or latest version) Section 20 may be used to build confidence in the
equipment’s HIRF immunity before conducting integrated system laboratory tests
in Step 5. The equipment should be specified and tested in accordance with the
test levels (wire bundle currents injection and RF field illumination) of
RTCA/DO-160/EUROCAE ED-14 Section 20 or to a level estimated for the aircraft
and equipment installation using the applicable external HIRF environment.

2.         Equipment
HIRF tests may be used to augment the integrated system HIRF tests where
appropriate. For equipment whose HIRF immunity is evaluated as part of the
integrated system-level HIRF tests discussed in Step 5, the individual
equipment’s HIRF testing described in this step is optional.

e.         Step
5 — Integrated system test

1.         Radiated
and conducted RF susceptibility laboratory tests on an integrated system
should be performed for Level A systems. The HIRF field strengths and wire
bundle currents selected for this test should be based on the attenuated
external HIRF environment determined in the aircraft assessment (see Steps 10,
11, or 12). In many cases, the integrated system test is performed before the
aircraft assessment is complete. In these cases, the integrated system test
field strengths and currents should be selected based on the expected aircraft
attenuation or transfer function.

2.         The
installation details for the laboratory integrated system tests should be
similar to the installation in the aircraft. For example, the bonding and
grounding of the system, wire size, routing, arrangement (whether parallel or
twisted wires), connector types, wire shields, and shield terminations, and
the relative position of the elements to each other and the ground plane in
the laboratory should closely match the system installation on the aircraft to
be certified. For this reason, the laboratory integrated system rig should
have an Agency conformity inspection prior to conducting any Agency
certification credit testing.

3.         The
integrated system should be tested with the system operating, to include
connected displays, sensors, actuators, and other pieces of equipment.
Applicants should place the system in various operating modes to ensure the
integrated system is tested when operating at its maximum sensitivity. If the
connected equipment is not related to the functions with catastrophic
failures, these items may be simulated by test sets, if the test sets
accurately represent the terminating circuit impedance of the sensor. However,
the connected equipment should meet the appropriate HIRF requirements required
for its failure condition classification.

4.         The test
levels should be selected based on the expected aircraft internal HIRF
environment determined through aircraft tests (see Step 10), generic transfer
functions ‘for Level A display systems only’ and attenuation (see Step 11), or
aircraft similarity assessment (see Step 12), using the applicable external
HIRF environment. Integrated system test procedures are described in detail in
the User’s Guide (SAE ARP 5583A/EUROCAE ED-107A).

5.         Wire
bundle current injection should be used for frequencies from 10 kHz to 400
MHz. RF currents are injected into the integrated system wiring via a current
transformer. Each wire bundle in the system should be injected and the induced
wire bundle current measured. If a system wire bundle branches, then each wire
bundle branch should also be tested. Simultaneous multi-bundle current
injection may be necessary on systems with redundant or multi-channel
architectures.

6.         High-level
radiated susceptibility tests should be used at frequencies greater than 100
MHz. The radiating antenna should be far enough away to ensure the total
volume of the equipment and at least half a wavelength of the wiring is
simultaneously and uniformly illuminated during the test.

7.         The
applicant should define appropriate pass/fail criteria for the system, based
on the system safety assessment and the appropriate HIRF requirements. Any
system susceptibility, including system malfunctions such as displaying
hazardously misleading information, upsets, or damage, should be recorded and
evaluated based on these previously defined pass/fail criteria.

8.         Using only
the modulation to which the system under evaluation is most sensitive may
minimise the test time. The User’s Guide (SAE ARP 5583A/EUROCAE ED-107A)
provides guidance on modulation selection and suggested default modulations
and dwell times.

9.         The
equipment tests in Step 4, using the techniques in RTCA/DO-160G/EUROCAE ED-14G
(or latest version) Section 20, normally are not sufficient to show HIRF
compliance for Step 5 and Step 6. However, these standard RTCA/DO-160G/EUROCAE
ED-14G Section 20 tests may be sufficient if paragraph 7(e)(2) and (3) of this
step are met.

10.      If the Level
A System consists of multiple similar channels, the applicant may propose
using one or more channels in the laboratory test set-up for the integrated
system, instead of all similar channels. The applicant should demonstrate that
the laboratory test set-up adequately performs the functions that must
demonstrate compliance with CS 23.1308(a), 25.1317(a), 27.1317(a), and
29.1317(a). The applicant should ensure that the laboratory test set-up
represents and monitors any cross-channel interactions, such as cross-channel
data links, redundancy management, and system health monitoring.

Note: Similar channels are composed
of equipment that has the same hardware but not necessarily the same part
number; in case of use of pin programming and/or software to identify or
configure equipment of similar channels, it must be assessed whether these
differences have an impact on the functions performed.

f.          Step
6 — System similarity assessment

1.         The
integrated system HIRF tests performed for a system previously certified on agiven
aircraft model may be used to demonstrate system verification for a similar
system. Each system considered under the similarity approach needs to be
assessed independently even if it may use equipment and installation
techniques from previous certification projects.

2.         The system
used as the basis for similarity must have successfully completed integrated
system HIRF tests. A similarity assessment requires a comparison of both the
equipment and installation differences that could adversely affect HIRF
immunity. The assessment should evaluate the differences between the
previously HIRF certified system and the equipment circuit interfaces, wiring,
grounding, bonding, connectors, and wire-shielding practices of the equipment that
is part of the new system.

3.         If the
assessment finds only minimal differences between the previously certified
system and the new system to be certified, similarity may be used as the basis
for system-level verification without the need for additional integrated
system tests, provided there are no unresolved in-service HIRF problems
related to the previously certified system. If there is uncertainty about the
effects of the differences, additional tests and analyses should be conducted,
as necessary and appropriate, to resolve the uncertainty. The amount of
additional testing should be commensurate with the degree of difference
identified between the new system and the system previously certified. If
significant differences are found, similarity should not be used as the basis
for system-level verification.

g.         Step
7 — Aircraft assessment decision

1.         Level A
systems require an aircraft assessment. The aircraft assessment should
determine the actual internal HIRF environment where the Level A systems are
installed in the aircraft. The applicant should choose whether to use aircraft
tests, previous coupling/attenuation data from similar aircraft types
(similarity). For Level A display systems only, applicants should use the
generic transfer functions and attenuation in [Appendix 1](#_DxCrossRefBm1926189330) to this AMC. Alternately, the
aircraft assessment may be a test that exposes the entire aircraft with
operating Level A systems to external HIRF Environment I, II, or III (Tables
2, 3, and 4 respectively), as appropriate, to demonstrate acceptable Level A
system performance.

2.         Level A
display systems include the display equipment, control panels, and the sensors
that provide information to the displays. These sensors could also provide
information to Level A non-display systems, so in that case, the applicant
should determine the real transfer function and attenuation curves of these
sensors when demonstrating compliance for this Level A non-display system. For
example, for air data systems and inertial reference systems, which send
information to the EFIS and flight controls, the transfer function and
attenuation should be determined by aircraft low-level coupling testing or an aircraft
similarity assessment as defined in Steps 10 and 12.

3.         Other
methods for aircraft HIRF assessment, such as analysis, may be acceptable.
However, comprehensive modelling and analysis for RF field coupling to the
aircraft structure is an emerging technology. Therefore, analysis alone is
currently not adequate to show HIRF compliance for Level A systems and should
be augmented by testing.

4.         If
analysis is used to determine aircraft attenuation and transfer function
characteristics, test data should be provided to support this analysis. Any
analysis results should take into account the quality and accuracy of the
analysis. Significant testing, including aircraft-level testing, may be
required to support the analysis.

5.         Aircraft
and system tests and assessments need not be performed for the HIRF
environments above 18 GHz if data and design analysis show the integrated
system test results (see Step 5) satisfy the pass/fail criteria from 12 to 18
GHz, and the systems have no circuits operating in the 18 to 40 GHz frequency
range.

h.         Step
8 — Aircraft test decision

1.         Various
aircraft test procedures are available and accepted for collecting data for
aircraft HIRF verification. The two main approaches to aircraft testing are
the aircraft high-level test (see Step 9) and the aircraft low-level coupling
test (see Step 10). The aircraft high-level field-illumination test involves
radiating the aircraft at test levels equal to the applicable external HIRF
environment in the HIRF requirements. Aircraft low-level coupling tests
involve measuring the airframe attenuation and transfer functions, so that the
internal HIRF electric fields and currents can be compared with the integrated
system test levels.

2.         Some test
procedures may be more appropriate than others because of the size of the
aircraft and the practicality of illuminating the entire aircraft with the
appropriate external HIRF environment. The aircraft low-level coupling tests
(see Step 10) may be more suitable for testing large aircraft than the
high-level field-illumination test in Step 9, which requires illumination of
the entire aircraft with the external HIRF environment.

i.          Step
9 — Aircraft high-level tests

1.         The
aircraft high-level field-illumination test requires generating RF fields
external to an aircraft at a level equal to the applicable external HIRF
environment.

2.         At
frequencies below 400 MHz, the distance between the aircraft and the
transmitting antenna should be sufficient to ensure the aircraft is
illuminated uniformly by the external HIRF environment. The transmitting
antenna should be placed in at least four positions around the aircraft. For
aircraft, the antenna is typically placed to illuminate the nose, tail, and
each wingtip. For rotorcraft, the antenna is typically placed to illuminate
the nose, tail, and each side. The aircraft should be illuminated by the
antenna at each position while sweeping the frequency range. Perform separate
frequency sweeps with the transmitting antenna oriented for horizontal and
vertical polarisation. The RF field should be calibrated by measuring the RF
field strength in the centre of the test volume before the aircraft is placed
there.

3.         At
frequencies above 400 MHz, the RF illumination should be localised to the
system under test, provided all parts of the system and at least one
wavelength of any associated wiring (or the total length if less than one
wavelength) are illuminated uniformly by the RF field. The applicant may need
reflection planes to illuminate relevant apertures on the bottom and top of
the aircraft.

4.         To ensure
the systems are tested when operating at their maximum sensitivity, Level A
systems should be fully operational, and the aircraft should be placed in
various simulated operating modes.

5.         The test
time can be minimised by using only the modulation to which the system under
evaluation is most sensitive. If the applicant does this, the rationale used
to select the most sensitive modulation should be documented in the HIRF test
plan as discussed in Section 6(b)(1). The User’s Guide (SAE ARP 5583A/EUROCAE
ED-107A) provides guidance on modulation selection and suggested default
modulations and dwell times.

6.         As an
alternative to testing at frequencies below the first airframe resonant
frequency, it is possible to inject high-level currents directly into the
airframe using aircraft high-level direct-drive test methods. Aircraft skin
current analysis should be performed as described in the User’s Guide, or
low-level swept‑current measurements should be made to determine the skin
current distribution that will exist for different RF field polarisations and
aircraft illumination angles so that these can be simulated accurately during
this test. Aircraft high-level direct-drive testing, although applicable only
from 10 kHz to the first airframe resonant frequency, is advantageous because
it is possible to test all systems simultaneously.

j.          Step
10 — Aircraft low-level coupling tests

1.         General

(a)       The
aircraft low-level coupling tests include three different tests that cover the
frequency range of 10 kHz to 18 GHz (see Figure 2). Detailed descriptions are
available in the User’s Guide. Other techniques may be valid, but must be
discussed with and accepted by the Agency before being used.

(b)       The
low-level direct-drive test (see Step 10b, Figure 2) and the low-level
swept-current test (see Step 10c) are used for frequencies at or below 400
MHz. The low-level swept-field test (see Step 10d) is used for frequencies at
and above 100 MHz. There is an overlap of test frequencies from 100 to 400 MHz
in the low-level swept-current test and the low-level swept-field test. The
division at 100 MHz is not absolute and depends on the aircraft to be tested
and the resonance of the wiring and instrumentation limitations. The division
at 400 MHz is not absolute either, and depends on when HIRF penetration of the
equipment case becomes a significant factor.

2.         Steps
10a and 10b — Aircraft skin current analysis and low-level direct-drive test.
Low-level direct‑drive tests in conjunction with skin current analysis should
be used to determine the transfer function between the skin current and
individual equipment wire bundle currents. The low-level direct‑drive test is
typically used for frequencies from 10 kHz to the first airframe resonant
frequency. For the low-level direct-drive test to be applied successfully, a
three-dimensional model of the aircraft should be derived using aircraft skin current
analysis. The three-dimensional model can then be used to derive the aircraft’s
skin current pattern for the applicable external HIRF environment. Guidance on
skin current analysis is in the User’s Guide. If the relationship between the
external HIRF environment and the skin current is known for all illumination
angles and polarisation, either because of aircraft skin current analysis or
the use of the low-level swept-current test, the skin current can be set up by
direct injection into the airframe. The resultant currents on the system wire
bundles are measured with a current probe and normalised to 1 V/m electric
field strength so they can be scaled to the appropriate external HIRF
environment. The low-level direct-drive test is more effective than low-level
swept‑current tests for frequencies from 10 kHz to the first airframe resonant
frequency, and may be necessary for small aircraft or aircraft with high
levels of airframe shielding.

3.         Step
10c — Low-level swept-current test. The low-level swept-current test
involves illuminating the aircraft with a low-level external HIRF field to
measure the transfer function between the external field and the aircraft and
equipment wire bundle currents. This test is typically used in the frequency
range of 500 kHz to 400 MHz. The transfer function is resonant in nature and
is dependent on both the aircraft structure and the system installation.
Because the transfer function relates wire bundle currents to the external
field, the induced bulk current injection test levels can be related to an
external HIRF environment.

The transmitting antenna should be placed in at least four
positions around the aircraft, with the distance between the aircraft and the
transmitting antenna sufficient to ensure the aircraft is illuminated
uniformly. For aircraft, the antenna is typically placed to illuminate the
nose, tail, and each wingtip. For rotorcraft, the antenna is typically placed
to illuminate the nose, tail, and each side. The aircraft should be
illuminated by the antenna at each position while sweeping the frequencies in
the range of 500 kHz to 400 MHz. The applicant should perform separate
frequency sweeps with the transmitting antenna oriented for horizontal and
vertical polarisation, and measure the currents induced on the aircraft wire
bundles.

The applicant should calculate the ratio between the induced
wire bundle current and the illuminating antenna field strength, and normalise
this ratio to 1 V/m. This provides the transfer function in terms of induced
current per external field strength unit. Then the current induced by the
applicable external HIRF environment can be calculated by multiplying the
transfer function by the external HIRF field strength. The calculated HIRF
currents for all transmitting antenna positions for each aircraft wire bundle to
beassessed should be overlaid to produce worst-case induced current for each
wire bundle. These worst-case induced currents can be compared with the
current used during the integrated system test in Step 5.

4.         Step
10d — Low-level swept-field test. Low-level swept-field testing is
typically used from 100 MHz to 18 GHz. The test procedures for the low-level
swept-field test are similar to those used for the low-level swept-current
test; however, in the low-level swept-field test, the internal RF fields in
the vicinity of the equipment are measured instead of the wire bundle
currents. Various techniques can be used to ensure the maximum internal field
in the vicinity of the equipment is measured. Depending on the size of the
aircraft and the size of the aircraft cabin, flight deck, and equipment bays,
multipoint measurement or mode stirring can be used to maximise the internal
field in the vicinity of the equipment. See the User’s Guide (SAE ARP
5583A/EUROCAE ED-107A) for detailed low-level swept-field test procedures.

k.         Step
11 — Generic transfer functions and attenuation — Level A display systems only

1.         Level A
displays involve functions for which system information is displayed directly
to the pilot. For Level A display systems, the aircraft attenuation data may
be determined using generic attenuation and transfer function data. This
approach should not be used for other Level A systems, such as control
systems, because failures and malfunctions of those systems can more directly
and abruptly contribute to a catastrophic failure event than display system
failures and malfunctions; therefore, other Level A systems should have a more
rigorous HIRF compliance verification programme.

2.         The
integrated system test levels specified in Step 5 may be derived from the
generic transfer functions and attenuation for different types of aircraft.
Acceptable transfer functions for calculating the test levels are given in [Appendix 1](#_DxCrossRefBm1926189330) to this AMC.[Appendix 1](#_DxCrossRefBm1926189330) to this AMC also contains
guidelines for selecting the proper generic attenuation. The generic transfer
functions show the envelope of the currents that might be expected to be
induced in the types of aircraft in an external HIRF environment of 1 V/m. The
current levels should be multiplied linearly by HIRF Environment I, II, or
III, as appropriate, to determine the integrated system test levels.

3.         The
internal HIRF electric field levels are the external HIRF environment divided
by the appropriate attenuation, in linear units. For example, 20 dB or a 10:1
attenuation means the test level is the applicable external HIRF environment
electric field strength reduced by a factor of 10.

4.         The
internal HIRF environments for Level A display systems can also be measured
using on-aircraft low‑level coupling measurements of the actual system
installation (see Step 10). This procedure should provide more accurate
information to the user, and the test levels may be lower than the generic
transfer functions or attenuation, which are worst-case estimates.

l.          Step
12 — Aircraft similarity assessment

1.         The
aircraft attenuation and transfer function tests performed for a previously
certified aircraft may be used to support aircraft-level verification for a
similar aircraft model. The aircraft used as the basis for similarity must
have been previously certified for HIRF compliance, using HIRF attenuation and
transfer functions determined by tests on that aircraft.

2.         The
similarity assessment for the new aircraft model should consider the aircraft
differences that could impact on the internal HIRF environment affecting the
Level A systems and the associated wiring. The comparison should consider
equipment and wiring locations, airframe materials and construction, and
apertures that could affect attenuation for the external HIRF environment.

3.         If the
assessment finds only minimal differences between the previously certified
aircraft and the new aircraft to be certified, similarity may be used to
determine the aircraft attenuation and transfer functions without the need for
additional aircraft tests, providing there are no unresolved in-service HIRF
problems related to the existing aircraft. If there is uncertainty about the
effects of the differences, additional tests and analyses should be conducted
as necessary and appropriate to resolve the uncertainty. The amount of
additional testing should be commensurate with the degree of difference
identified between the new aircraft to be certified and the aircraft
previously certified. If significant differences are found, similarity should
not be used as the basis for aircraft-level verification.

m.       Step
13 — Assess the immunity

1.         The
applicant should compare the test levels used for the integrated system test
of Step 5 with the internal RF current or RF fields determined by the aircraft
low-level coupling tests (see Step 10), the generic transfer functions and
attenuation (see Step 11), or the aircraft similarity assessment (see Step
12). The actual aircraft internal RF currents and RF fields should be lower
than the integrated system test levels.The comparison method should be
included in the HIRF compliance plan. The method should enable a direct
comparison between the system test level and the aircraft internal HIRF
environment at the equipment or system location, using current for frequencies
from 10 kHz to 400 MHz, and using electric field strength for frequencies from
100 MHz through 18 GHz.

2.         If the
conducted RF susceptibility test levels used for the integrated system test
(see Step 5) were too low when compared with the aircraft-induced currents
determined in Steps 10b, 10c, 11 or 12, then corrective measures are needed
(see Step 14). If the radiated RF susceptibility test levels used for
integrated system tests (see Step 5) were too low when compared with the
aircraft internal fields determined in Steps 10d, 11 or 12, then corrective
measures are needed (see Step 14).

3.         When
comparing the current measured during low-level swept-current tests in Step
10c with the current used during the integrated system tests in Step 5, there
may be differences. These differences may be due to variations between the
actual aircraft installation and the integrated system laboratory
installation, such as wire bundle lengths, shielding and bonding, and wire
bundle composition. The worst-case current signature for a particular wire
bundle should be compared with the current induced at the particular test
level or equipment malfunction over discrete frequency ranges such as
50 to 500 kHz, 500 kHz to 30 MHz, and 30 to 100 MHz. This comparison
should be broken into discrete frequency ranges because the resonant
frequencies may differ between the integrated system tests and the aircraft
tests.

4.         If the
applicant uses aircraft high-level tests (see Step 9) for aircraft HIRF
verification, they should determine whether there were any Level A system
susceptibilities. Any Level A system susceptibilities should be evaluated
based on the pass/fail criteria as established in the test plan (see Section 8(b)(1)).
If the HIRF susceptibilities are not acceptable, then corrective measures may
be needed (seeStep 14).

5.         HIRF
susceptibilities that were not anticipated or defined in the test plan
pass/fail criteria may be observed during aircraft high-level tests or
integrated system laboratory tests. The pass/fail criteria may be modified if
the effects neither cause nor contribute to conditions that adversely affect
the aircraft functions or systems in the HIRF requirements. The applicant
should provide an assessment and the supporting rationale for any
modifications to the pass/fail criteria to the Agency for acceptance.

If the HIRF susceptibilities are not acceptable, then
corrective measures may be needed (see Step 14).

6.         If the
Level A systems show no adverse effects when tested to levels derived from the
applicable HIRF Environment I or III, this also demonstrates compliance of the
system with HIRF Environment II.

7.         If the
integrated system test results (see Step 5) satisfy the pass/fail criteria
from 12 to 18 GHz, and design analysis shows the system has no circuits
operating in the 18 to 40 GHz frequency range, this demonstrates by analysis
that the system is not adversely affected when exposed to HIRF environments
above 18 GHz. If these conditions are satisfied, further aircraft and system
tests and assessments above 18 GHz are not necessary.

8.         The
applicant should review the actual system installation in the aircraft and the
system configuration used for the integrated system test (see Step 5). If
significant configuration differences are identified, corrective measures may
be needed (see Step 14).

9.         Certain RF
receivers with antennas connected should not be expected to perform without
effects during exposure to the HIRF environments, particularly in the RF
receiver operating band. Because the definition of adverse effects and the RF
response at particular portions of the spectrum depends on the RF receiver
system function, the applicant should refer to the individual RF receiver
minimum performance standards for additional guidance. However, because many
RF receiver minimum performance standards were prepared before the implementation
of the HIRF requirements, the RF receiver pass/fail criteria should be
coordinated with the Agency.

10.      The
applicant should provide the similarity assessment and the supporting
rationale to the Agency for acceptance.

n.         Step
14 — Corrective measures. Corrective measures should be taken if the
system fails to satisfy the HIRF immunity assessment of Step 13. If changes or
modifications to the aircraft, equipment, system or system installation are
required, then additional tests may be necessary to verify the effectiveness
of the changes. The RTCA/DO-160G/EUROCAE ED-14G, or latest version, Section 20
equipment tests, integrated system tests, and aircraft tests, in whole or in
part, may need to be repeated to show HIRF compliance.

o.         Step
15 — HIRF protection compliance. The test results and compliance report
should be submitted to the Agency for approval as part of the overall aircraft
type certification or supplemental type certification process.

Figure 3: Routes to HIRF compliance — Level B and Level
C systems

![Aviation.Bot AI suggestion, not from EASA source: **Overall Summary:** This image presents a flowchart illustrating the process for demonstrating High-Intensity Radiated Fields (HIRF) compliance for Level B and Level C aircraft systems.

**Detailed Description:**
The image displays a flowchart composed of rectangular process boxes, diamond-shaped decision points, and directional arrows connecting them. All elements are outlined in black against a white background.

1.  **System safety assessment (1):** This is the topmost element, a rectangular box containing the text "System safety assessment" on the first line and "(1)" on the second line.
2.  **Text Label:** Directly below the "System safety assessment (1)" box, centered above the subsequent arrow, is the text "Level B or Level C system".
3.  **Define aircraft and system HIRF protection (2):** An arrow points downwards from "System safety assessment (1)" to this rectangular box. This box contains the text "Define aircraft and system HIRF protection" on three lines and "(2)" on the fourth line.
4.  **Select compliance method (3):** An arrow points downwards from "Define aircraft and system HIRF protection (2)" to this diamond-shaped decision box. This box contains the text "Select compliance method" on two lines and "(3)" on the third line.
5.  **Similarity assessment (5):** An arrow points horizontally to the left from the "Select compliance method (3)" decision box to this rectangular box. The arrow is labeled "Similarity". The box contains the text "Similarity assessment" on two lines and "(5)" on the third line.
6.  **Equipment test (4):** An arrow points vertically downwards from the "Select compliance method (3)" decision box to this rectangular box. The arrow is labeled "Equipment-level verification". The box contains the text "Equipment test" on two lines and "(4)" on the third line.
7.  **Assess the immunity (6):** This is a diamond-shaped decision box located below and horizontally centered between "Similarity assessment (5)" and "Equipment test (4)". An arrow points downwards from "Similarity assessment (5)" to this box, and another arrow points downwards from "Equipment test (4)" to this box. The box contains the text "Assess the immunity" on two lines and "(6)" on the third line.
8.  **HIRF protection compliance (8):** An arrow points vertically downwards from the "Assess the immunity (6)" decision box to this rectangular box. The arrow is labeled "Acceptable". The box contains the text "HIRF protection compliance" on two lines and "(8)" on the third line.
9.  **Corrective measures (7):** An arrow points horizontally to the right from the "Assess the immunity (6)" decision box to this rectangular box. The arrow is labeled "Unacceptable". The box contains the text "Corrective measures" on two lines and "(7)" on the third line.
10. **Feedback Loop:** An arrow points horizontally to the left from "Corrective measures (7)", then turns vertically upwards, and finally turns horizontally to the left again, pointing to the "Define aircraft and system HIRF protection (2)" rectangular box, completing a feedback loop.

**Contextual Linkage:**
The flowchart outlines a sequential, yet iterative, process for achieving HIRF compliance for Level B and Level C systems. It begins with a system safety assessment (1) to classify the system. For Level B or Level C systems, the process proceeds to defining HIRF protection (2). A key decision point (3) allows for two paths: either a "Similarity" assessment (5) based on previous certifications or an "Equipment-level verification" via an "Equipment test" (4). Both paths converge at the "Assess the immunity" step (6). If the immunity is "Acceptable", the process concludes with "HIRF protection compliance" (8). If the immunity is "Unacceptable", "Corrective measures" (7) are required, leading back to the "Define aircraft and system HIRF protection" step (2) for re-evaluation and potential design changes, indicating an iterative loop until compliance is achieved.

**Mermaid Markdown:**
"mermaid
graph TD
    A[System safety assessment (1)] -->|"Level B or Level C system"| B[Define aircraft and system HIRF protection (2)]
    B --> C{Select compliance method (3)}
    C -- Similarity --> D[Similarity assessment (5)]
    C -- Equipment-level verification --> E[Equipment test (4)]
    D --> F{Assess the immunity (6)}
    E --> F
    F -- Acceptable --> G[HIRF protection compliance (8)]
    F -- Unacceptable --> H[Corrective measures (7)]
    H --> B
"](file_tNNDI2wQkpg/image074.png)

(n) = Step number as described in Section 10 of this
AMC

8.         STEPS
TO DEMONSTRATE ‘LEVEL B’ AND ‘LEVEL C’ SYSTEM HIRF COMPLIANCE

Figure 3 illustrates a process that the applicant can use to
demonstrate whether their Level B and Level C systems comply with
CS23.1308(b), 25.1317(b), 27.1317(b), and 29.1317(b), and with CS23.1308(c), 25.1317(c),
27.1317(c), and 29.1317(c) respectively.

**a.         Step 1 — HIRF safety assessment.** The
applicant should determine the system certification level for the systems to be
certified on their aircraft, using a system safety assessment as discussed in Section
6(b)(2). For systems classified with hazardous or major failure conditions
(Level B and Level C systems), the applicant should follow compliance Steps 2
through 8 listed below, as appropriate. These compliance steps are also
depicted in Figure 3 of this AMC and are not necessarily accomplished
sequentially. For systems classified with catastrophic failure conditions
(Level A systems), the applicant should follow the compliance steps outlined
in Section 7.

**b.         Step 2 — Define the aircraft and
system HIRF protection.** The applicant should define the HIRF protection
features incorporated into the aircraft and system designs, based on the HIRF
test levels applicable to their aircraft and its Level B and Level C systems.
Equipment, system, and aircraft HIRF protection design may occur before
aircraft-level tests are performed, and before the actual internal HIRF
environment is determined. Therefore, the equipment, system and aircraft HIRF
protection design should be based on an estimate of the expected internal HIRF
environment.

**c.         Step 3 — Select the compliance method.**The applicant should determine whether to perform equipment HIRF tests on
the Level B and Level C systems, or to base the compliance on previous
equipment tests performed for a similar system.

**d.         Step 4 — Equipment test**

1.         Level B
and Level C systems do not require the same degree of HIRF compliance testing
as Level A systems and, therefore, do not require aircraft-level testing.
RTCA/DO-160G/EUROCAE ED-14G,or latest version, Section 20 laboratory test
procedures should be used, using equipment test levels defined in the applicable
specifications. The test levels used depend on whether the system is
categorised as Level B or Level C. Equipment HIRF test Level 1 or 2, as
applicable, should be used for Level B systems. RTCA/DO‑160/EUROCAE ED-14
Section 20 Category RR (using the alternative modulation for radiated
susceptibility) satisfies the requirements of equipment HIRF test Level 1. For
equipment HIRF test Level 2, the applicant may use the approach in Section 9(k)
to help determine the acceptable aircraft transfer function and attenuation
curves for their Level B system. Equipment HIRF test Level 3 should only be
used for Level C systems. RTCA/DO-160/EUROCAE ED-14 Section 20 Category TT
satisfies the requirements of equipment HIRF test Level 3. When applying
modulated signals, the test levels are given in terms of the peak of the test
signal as measured by a rootmeansquare (rms), indicating the spectrum
analyser’s peak detector. See the User’s Guide (SAE ARP 5583A/EUROCAE ED‑107A)
for more details on modulation.

2.         The
applicant should define appropriate pass/fail criteria for the system, based
on the system safety assessment and the appropriate HIRF requirements (see Section 6(b)(2)).
Any susceptibility noted during the equipment tests, including equipment
malfunctions, upsets, or damage, should be recorded and evaluated based on the
defined pass/fail criteria.

**e.         Step 5 — Similarity assessment**

1.         The
equipment HIRF tests performed for a system previously certified on a given
aircraft model may be used to show compliance for a similar system. Each
system considered for similarity needs to be assessed independently even if it
used equipment and installation techniques from a previous certification.

2.         The system
used as the basis for certification by similarity must have successfully
completed equipment HIRF tests and been previously certified for HIRF
compliance on another aircraft model. Similarity assessment requires a
comparison of both the equipment and installation differences that could
adversely affect HIRF immunity. An assessment of a new system should consider
the differences in the equipment circuit interfaces, wiring, grounding,
bonding, connectors, and wire-shielding practices.

3.         If the
assessment finds only minimal differences between the previously certified
system and the new system to be certified, similarity may be used for HIRF
compliance without the need for additional equipment HIRF tests, provided
there are no unresolved in-service HIRF problems related to the previously
certified system. If there is uncertainty about the effects of the
differences, additional tests and analyses should be conducted as necessary
and appropriate to resolve the uncertainty. The amount of additional testing
should be commensurate with the degree of difference identified between the
new system and the system previously certified. If significant differences are
found, similarity should not be used as the basis for HIRF compliance.

**f.          Step 6 — Assess the immunity**

1.         The
applicant should review the results of the equipment test to determine whether
the pass/fail criteria are satisfied. HIRF susceptibilities that were not
anticipated or defined in the test plan pass/fail criteria may be observed
during equipment HIRF tests. The pass/fail criteria may be modified if the
effects neither cause nor contribute to conditions that adversely affect the
aircraft functions or systems, as applicable, in the HIRF requirements. The
applicant should provide an assessment of, and the supporting rationale for,
any modifications to the pass/fail criteria to the Agency for approval. If the
HIRF susceptibilities are not acceptable, then corrective measures may be
needed (see Step 7).

2.         The
applicant should review the actual system installation in the aircraft and the
configuration used for the equipment tests (see Step 4). If significant
differences in grounding, shielding, connectors, or wiring are identified,
corrective measures may be needed (see Step 7).

3.         Certain RF
receivers with antennas connected should not be expected to perform without
effects during exposure to the HIRF environments, particularly in the RF
receiver operating band. Because the definition of adverse effects and the RF
response at particular portions of the spectrum depends on the RF receiver
system function, applicants should refer to the individual RF receiver minimum
performance standards for additional guidance. However, because many RF
receiver minimum performance standards were prepared before the implementation
of the HIRF requirements, the RF receiver pass/fail criteria should be
coordinated with the Agency. Future modifications of the minimum performance
standards should reflect the HIRF performance requirements.

**g.         Step 7 — Corrective measures.** The
applicant should take corrective measures if the system fails to satisfy the
HIRF immunity assessment of Step 6. If changes or modifications to the
equipment, system, or system installation are required, then additional tests
may be necessary to verify the effectiveness of the changes. The
RTCA/DO-160G/EUROCAE ED-14G,or latest version, Section 20 equipment tests, in
whole or in part, may need to be repeated to show HIRF compliance.

**h.         Step 8 — HIRF protection compliance.** The
applicant shouldsubmit the test results and compliance report to the Agency
for acceptance as part of the overall aircraft type certification or
supplemental type certification process.

9.         HIRF
COMPLIANCE DEMONSTRATION

**a.         HIRF compliance plan.** An overall
HIRF compliance plan should be established to clearly identify and define HIRF
certification requirements, HIRF protection development, and the design, test,
and analysis activities intended to be part of the compliance effort. This
plan should provide definitions of the aircraft systems, installations, and
protective features against which HIRF compliance will be assessed. The HIRF
compliance plan should be discussed with, and submitted to, the Agency for
acceptance before initiating HIRF compliance activities. If the aircraft,
system, or installation design changes after approval, a revised HIRF
compliance plan should be submitted to the Agency for acceptance. The HIRF
compliance plan should include the following:

1.         a HIRF
compliance plan summary;

2.         identification
of the aircraft systems, with classifications based on the safety assessment
as it relates to HIRF (seeSection 6(b)(2));

3.         the
planned or expected HIRF environment for the aircraft and installed systems;
and

4.         the
verification methods, such as test, analysis, or similarity.

**b.         Methods of compliance verification**

1.         Various
methods are available to aid in demonstrating HIRF compliance. Methods
acceptable to the Agency are described in Sections 6 and 7 of this AMC.
Figures 1 and 2 above outline the steps to HIRF compliance for systems that requireLevel
A HIRF certification. Figure 3 above outlines the steps to HIRF compliance for
systems that require Level B or Level C HIRF certification. The steps in these
figures are not necessarily accomplished sequentially. Wherever a decision
point is indicated on these figures, the applicant should complete the steps
in that path as described in Sections 6 and 7 of this AMC.

2.         Other HIRF
compliance techniques may be used to demonstrate system performance in the
HIRF environment; however, those techniques should be accepted by the Agency
before using them.

**c.         HIRF verification test, analysis, or
similarity plan.** Test, analysis and similarity are all acceptable methods.
The applicant must choose the method or the combination of methods most
appropriate for their project. See Sections 6 and 7 of this AMC, and SAE ARP 5583A/EUROCAE
ED-107A for additional guidance for selecting the appropriate method. Specific
HIRF test, analysis, or similarity plans could be prepared to describe
specific verification activities. A single verification plan combining various
methods for all the selected systems or dedicated verification plans may be
necessary. For example, there may be several systems or equipment laboratory
test plans, an aircraft test plan, or a similarity plan for selected systems
on an aircraft.

1.         Test
plan

(a)       A HIRF
compliance test plan may include the equipment, system, and aircraft test
objectives for the acquisition of data to support HIRF compliance
verification. The plan should provide an overview of the factors to be
addressed for each system testrequirement.

The test plan should include:

1.         the
purpose of the test;

2.         a
description of the aircraft and/or the system to be tested;

3.         system
configuration drawings;

4.         the
proposed test set-up and methods;

5.         the
intended test levels, modulations, and frequency bands;

6.         pass/fail
criteria; and

7.         the test schedule
and test location.

(b)       The test
plan should cover Level A, B, and C systems and equipment, as appropriate.
Level A systems may require both integrated systems laboratory tests and
aircraft tests. Level B and Level C systems and equipment require only
equipment laboratory testing.

(c)       The test
plan should describe the appropriate aspects of the systems to be tested and
their installation. Additionally, the test plan should reflect the results of
any analysis performed in the overall process of the HIRF compliance
evaluation.

**2.         Analysis plan.** A HIRF compliance
analysis plan should include the objectives, both at system and equipment
level, for generating data to support HIRF compliance verification.
Comprehensive modelling and analysis for RF field coupling to aircraft systems
and structures is an emerging technology; therefore, the analysis plan should
be coordinated with the Agency to determine an acceptable scope for the
analysis.

The analysis plan should include:

(a)       the purpose
and scope of the analysis;

(b)       a
description of the aircraft and/or the system addressed by the analysis;

(d)       the
proposed analysis methods;

(e)       the
approach for validating the analysis results; and

(f)        pass/fail
criteria, including margins to account for analysis uncertainty.

**3.         Similarity plan.** A similarity plan
should describe the approach undertaken to use the certification data from
previously certified systems, equipment, and aircraft in the proposed HIRF
compliance programme.

The similarity plan should include:

(a)       the purpose
and scope of the similarity assessment;

(b)       the
specific systems addressed by the similarity assessment;

(d)       details of
the significant differences between the aircraft and system to becertified and
the similar aircraft and system from which the data will be used; and

(e)       when data
has limited substantiation, a description and justification for margins to
account for similarity uncertainty;see Section 6(f)(3) for additional
information on margins.

**d.         Compliance reports.** One or more
compliance reports may be necessary to document the results of test, analysis,
or similarity assessments. For new or significantly modified aircraft, HIRF
compliance reports include many system and equipment test reports, aircraft
test reports, and HIRF vulnerability analysis reports. For these types of HIRF
certification programmes, a compliance summary report may be useful to
summarise the results of tests and analyses. For HIRF certification programmes
of relatively simple systems, a single compliance report is adequate.

**1.         Test reports.** Comprehensive test
reports should be produced at the conclusion of HIRF compliance testing. The
test reports should include descriptions of the salient aspects of equipment
or system performance during the test, details of any area of non-compliance
with HIRF requirements, actions taken to correct the non-compliance, and any
similarity declarations. The applicant should also provide the supporting
rationale for any deviations from system performance observed during testing.

**2.         Analysis reports.** Analysis reports
should describe the details of the analytical model, the methods used to
perform the analysis, and the results of the analysis. The reports should
identify any modelling uncertainty and justify the margins established in the
analysis plan.

**3.         Similarity reports.** Similarity
reports should document the significant aircraft, system, equipment, and
installation features that are common between the aircraft or system that is
the subject of the similarity analysis and the aircraft or system that was previously
certified for HIRF. The reports should identify all the significant
differences encountered, along with the assessment of the impact of these
differences on HIRF compliance. These reports should also justify the margins
established in the similarity plan.

10.       MAINTENANCE,
PROTECTION ASSURANCE, AND MODIFICATIONS

a.         The
minimum maintenance required to support HIRF certification should be
identified in the instructions for continued airworthiness (ICAs) as specified
in CS 23.1529, 25.1529, 25.1729, 27.1529, and 29.1529, as appropriate.
Dedicated devices or specific features may be required to provide HIRF
protection for an equipment or system installation. Appropriate maintenance
procedures should be defined for these devices and features to ensure
in-service protection integrity. A HIRF protection assurance programme should
be proposed in the certification plan to identify all actions necessary to
justify or to verify that the maintenance procedures are adequate. This
assurance programme may propose a surveillance programme based on a sampling
of the fleet for monitoring the effectiveness of the protection features
and/or maintenance procedures. The User’s Guide (SAE ARP 5583A/EUROCAE
ED107A) provides further information on these topics.

b.         The
maintenance procedures should consider the effects of corrosion, fretting,
flexing cycles, or other causes that could degrade these HIRF protection
devices. Whenever applicable, specific replacement times of these devices and
features should be identified.

c.         Aircraft
or system modifications should be assessed for the impact that any changes
will have on the HIRF protection. This assessment should be based on analysis
and/or measurement.

[Amdt 20/23]