9 You should perform a safety assessment related to HIRF 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 regulations. The failure condition classifications and terms used in this AC are like those used in AC 23.1309 -1, AC 25.1309-1, AC-27-1, and AC-29-2, as applicable.
Only those systems identified as performing or contributing to functions whose failure would result in catastrophic, hazardous, or major failure conditions are subject to HIRF regulations. Based on the failure condition classification established by the safety assessment, the systems should be assigned appropriate H CLs, as shown in table 1. The safety assessment should consider the common cause effects of HIRF, particularly for highly integrated systems and systems with redundant elements. The HIRF safety assessment determines the consequences of f ailures for the aircraft functions that are performed by the system.
7.3.1 HCL Classification The HCL classification assigned to the system and functions may be different from the design assurance level assigned for equipment redundancy, software, and complex electronic hardware. This is because HIRF environment s can cause common cause effects. The term “design assurance level ” should not be used to describe t he HCL because of the potential differences in assigned classifications for software, complex electronic hardware, and equipment redundancy. The HIRF safety assessment should include all electrical and electronic equipment, components , and electrical interconnections, and should assume 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 input information on the HIRF safety assessment. This information should only be used in the next phase activity in the section below to show compliance with the applicable paragraph of the HIRF regulations, after the required H CL for the system is determined by the HIRF safety assessment. The HIRF safety assessment should have input from and be coordinated between the applicant’s safety specialists, system specialists, and HIRF specialists. This process may vary from applicant to applicant. Further guidance on performing the safety assessment can be found in AC 23.1309-1, AC 25.1309-1, AC-27-1, AC-29-2, SAE ARP4754A, SAE ARP4761, and SAE ARP5583A.
Note: Considering that HIRF and lightning environments may have similar effects on electronic systems (disturbing electrical signals causing upsets or damage to circuits) and that the regulations for each are similarly structured, the system HCL and lightning certification level may be the same.
10 Table 1. HIRF Failure Conditions and System HIRF Certification Levels
HIRF REQUIREMENTS
EXCERPTS FROM §§ 23.1308, 25.1317, 27.1317, AND 29.1317
MOST SEVERE FAILURE
CONDITION OF THE
FUNCTION
SYSTEM HCL Each electrical and electronic system that performs a function whose failure would prevent the continued safe flight and landing of the rotorcraft/airplane… Catastrophic A Each electrical and electronic system that performs a function whose failure would significantly reduce the capability of the rotorcraft/airplane or the ability of the flightcrew to respond to an adverse operating condition… Hazardous B Each electrical and electronic system that performs a function whose failure would reduce the capability of the rotorcraft/airplane or the ability of the flightcrew to respond to an adverse operating condition… Major C
HIRF REQUIREMENTS
EXCERPTS FROM § 23.2520 (Amendment 23-65)
MOST SEVERE FAILURE
CONDITION OF THE
FUNCTION
SYSTEM HCL Each electrical and electronic system that performs a function, the failure of which would prevent the continued safe flight and landing of the airplane… Catastrophic A For airplanes approved for instrument flight rules (IFR) operations, each electrical and electronic system that performs a function, the failure of which would significantly reduce the capability of the airplane or the ability of the flightcrew to respond to an adverse operating condition… Hazardous B
7.3.2 Scope of HCL A Systems.
You must show compliance with §§ 23.1308(a), 23.2520(a), 25.1317(a), 27.1317(a), or § 29.1317(a) for each electrical and electronic system that performs a function whose failure would prevent continued safe flight and landing of the aircraft. Additionally, as required by §§ 23.1308(a)(2), 23.2520(a)(2), 25.1317(a)(2), 27.1317(a)(2), or § 29.1317(a)(2), the electrical and electronic system must recover norma l operation of the function in a timely manner after the airplane is exposed to the HIRF environment, unless the system’s recovery conflicts with other operational or functional requirements of the system. The electrical and electronic system includes all equipment, components, and electrical interconnections required for normal operation. Electrical and electronic equipment, components, and electrical interconnections that are operational only in non-normal situations do not have to meet the requirements o f §§ 23.1308(a),
23.2520(a), 25.1317(a), 27.1317(a) , or § 29.1317(a), provided all electrical and electronic equipment, components and electrical interconnections required for normal operation comply with these regulations.
7.3.3 Scope of HCL B and C Systems.
You must show compliance with § 23.1308(b) and (c), 23.2520(b), 25.1317(b) and (c),
27.1317(b) and (c), or§ 29.1317(b) and (c) for each system that performs a function whose failure would significantly reduce or reduce (paragraph (b) or (c) of the applicable HIRF regulations) the capability of the aircraft or the ability of the flightcrew to respond to an adverse operating condition when all electrical and electronic equipment, components , and electrical interconnections are exposed to HIRF test level 1, 2, or 3, respectively. As required by§ 23.2520(b), for IFR operations, the system must also recover normal operation of the function in a timely manner after the aircraft is exposed to the HIRF environment.
7.3.4 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 some systems have different failure conditions in different phases of flight .
Therefore, the HCL in table 1 corresponds to phase of flight with 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.
7.4 Establish the Applicable Aircraft External HIRF Environment.
The external HIRF environments I, II, and III, as published in §§ 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. Section 23.2520 does not specify external HIRF environments .
Note: For part 23, the applicant may use the guidance in this AC as a means of compliance, which may include ASTM consensus standards, accepted by the Administrator in accordance with § 23.2010 (See paragraph 4.4).
Table 2. HIRF Environment I FREQUENCY FIELD STRENGTH (V/m) PEAK FIELD STRENGTH (V/m) Average 10 kHz - 2 MHz 50 50 2 MHz - 30 MHz 100 100 30 MHz - 100 MHz 50 50 100 MHz – 400 MHz 100 100 400 MHz – 700 MHz 700 50 700 MHz - 1 GHz 700 100 1 GHz - 2 GHz 2,000 200 2 GHz - 6 GHz 3,000 200 6 GHz - 8 GHz 1,000 200 8 GHz - 12 GHz 3,000 300 12 GHz - 18 GHz 2,000 200 18 GHz - 40 GHz 600 200 Note: In this table, the higher field strength applies at the frequency band edges.
Table 3. HIRF Environment II FREQUENCY FIELD STRENGTH (V/m) PEAK (V/m) AVERAGE 10 kHz – 500 kHz 20 20 500 kHz - 2 MHz 30 30 2 MHz - 30 MHz 100 100 30 MHz – 100 MHz 10 10 100 MHz – 200 MHz 30 10 200 MHz – 400 MHz 10 10 400 MHz – 1 GHz 700 40 1 GHz - 2 GHz 1,300 160 2 GHz - 4 GHz 3,000 120 4 GHz - 6 GHz 3,000 160 6 GHz - 8 GHz 400 170 8 GHz - 12 GHz 1,230 230 12 GHz - 18 GHz 730 190 18 GHz - 40 GHz 600 150 Note: In this table, the higher field strength applies at the frequency band edges.
13 Table 4. HIRF Environment III FREQUENCY FIELD STRENGTH (V/m) PEAK FIELD STRENGTH (V/m) AVERAGE 10 kHz – 100 kHz 150 150 100 kHz – 400 MHz 200 200 400 MHz – 700 MHz 730 200 700 MHz 1 GHz 1,400 240 1 GHz 2 GHz 5,000 250 2 GHz 4 GHz 6,000 490 4 GHz 6 GHz 7,200 400 6 GHz 8 GHz 1,100 170 8 GHz - 12 GHz 5,000 330 12 GHz - 18 GHz 2,000 330 18 GHz - 40 GHz 1,000 420 Note: In this table, the higher field strength applies at the frequency band edges.
7.5 Establish the Test Environment for Installed Systems.
The external HIRF environment will penetrate the aircraft and establish an internal RF environment to which installed elect rical 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.
7.5.1 Level A Systems.
The resulting internal HIRF environments for level A systems are determined by aircraft attenuation to the external HIRF environments I, II, or III, as defined in appendix J to part 23 (Amendment 23-57), appendix L to part 25, appendix D to part 27, and appendix E to part 29, as applicable. The attenuation is aircraft - and zone-specific and should be established by aircraft test, analysis, or similarity. Paragraph 10 of this AC contains the steps for showing level A systems HIRF compliance.
7.5.2 Level B Systems.
The internal RF environments for level B systems are defined in appendix J to part 23 (Amendment 23-57), appendix L to part 25, appendix D to part 27, and appendix E to part 29, as applicable, as equipment HIRF test levels 1 or 2. Paragraph 11 of this AC contains the steps for showing level B systems HIRF compliance.
7.5.3 Level C Systems.
The internal RF environment for level C systems is defined in appendix J to part 23 (Amendment 23-57), appendix L to part 25, appendix D to part 27, and appendix E to part 29, as applicable, as equipment HIRF test level 3. Paragraph 11 of this AC contains the steps for showing level C systems HIRF compliance.
7.6 Apply the Appropriate Method of HIRF Compliance Verification.
Tables 5 and 6 summarizes the relationship between the aircraft performance requirements in sections (a), (b), and (c) of the applicable HIRF regulations, and the HIRF environments and test levels. Paragraph 7.8 below discusses section (d) of the HIRF regulations regarding previously issued special conditions .
7.6.1 Pass/Fail Criteria.
You should establish specific HIRF compliance pass/fail criteria for each system as they relate to the applicable HIRF regulation perfor mance criteria. Paragraph 5 of this AC provides the definitions of “normal operation” and “automatically recover” in the context of the requirement in §§ 23.1308(a)(2), 25.1317(a)(2), 27.1317(a)(2), and
29.1317(a)(2). Section 23.2520(a)(2) and (b) uses the phrase “recovers normal operation,” which allows manual recovery (flightcrew action) or automatic recovery of a system’s function after exposure to HIRF . You should present these pass/fail criteria to the FAA for approval. The means for monitoring system performance relative to these criteria should be established by the applicant and approved by the FAA. All effects defining the pass/fail criteria should be the result of identifiable and traceable analysis that includes both the separate and interdependent operational characteristics of the systems.
7.6.2 Evaluate Failures.
The analysis should evaluate the failures, either singularly or in combination, which could adversely affect system performance. This should include failures that could negate any system redundancy or influence more than one system performing the same function.
15 Table 5. HIRF Certification Requirements Summary for Parts 23 (Amendment 23 -57), 25, 27, and 29
HIRF FAILURE CONDITION FROM §§ 23.1308, 25.1317,
27.1317, AND 29.1317
PERFORMANCE
CRITERIA
ITEM THE
ENVIRONMENT OR
TEST LEVEL
APPLIES TO
HIRF ENVIRONMENT
OR TEST LEVEL Each electrical and electronic system that performs a function whose failure would prevent the continued safe flight and landing of the airplane/rotorcraft must be designed and installed so that— each function is not adversely affected during and after the time… airplane/rotorcraft… is exposed to the HIRF environment I.
Each electrical and electronic system that performs a function whose failure would prevent the continued safe flight and landing of the rotorcraft must be designed and installed so that each electrical and electronic system automatically recovers normal operation of that function, in a timely manner after… airplane/rotorcraft… is exposed to HIRF environment I, unless this conflicts with other operational or functional requirements of that system.
Each electrical and electronic system that performs a function whose failure would prevent the continued safe flight and landing of the airplane/rotorcraft must be designed and installed so that each electrical and electronic system is not adversely affected during and after… airplane/rotorcraft… is exposed to the HIRF environment II.
Each electrical and electronic system that performs a function whose failure would prevent the continued safe flight and landing of the rotorcraft must be designed and installed so that each function required during operation under visual flight rules is not adversely affected during and after… rotorcraft…. is exposed to HIRF environment III (Parts 27 and 29 only).
Each electrical and electronic system that performs a function whose failure would significantly reduce the capability of the airplane/rotorcraft or the ability of the flightcrew to respond to an adverse operating condition must be designed and installed so that— the system is not adversely affected when… equipment providing these functions… is exposed to equipment HIRF test level 1 or 2.
Each electrical and electronic system that performs such a function whose failure would reduce the capability of the airplane/rotorcraft or the ability of the flightcrew to respond to an adverse operating condition must be designed and installed so that— the system is not adversely affected when… equipment providing these functions… is exposed to equipment HIRF test level 3
16 Table 6. HIRF Certification Requirements Summary for Part 23 ( Amendment 23-65)
HIRF FAILURE CONDITION FROM § 23.2520
PERFORMANCE
CRITERIA
ITEM THE
ENVIRONMENT OR
TEST LEVEL
APPLIES TO
HIRF ENVIRONMENT
OR TEST LEVEL Each electrical and electronic system that performs a function, the failure of which would prevent the continued safe flight and landing of the airplane, must be designed, and installed such that— the function at the airplane level is not adversely affected during and after the time… airplane… is exposed to the HIRF environment.
Each electrical and electronic system that performs a function, the failure of which would prevent the continued safe flight and landing of the airplane, must be designed, and installed such that— the system recovers normal operation of that function in a timely manner after… airplane… is exposed to the HIRF environment unless the system's recovery conflicts with other operational or functional requirements of the system For airplanes approved for IFR operations, each electrical and electronic system that performs a function, the failure of which would significantly reduce the capability of the airplane or the ability of the flightcrew to respond to an adverse operating condition, must be designed and installed such that— the system recovers normal operation of that function in a timely manner after… airplane… is exposed to the HIRF environment.
7.7 Verify HIRF Protection Effectiveness.
You should show that the RF current 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.
7.8 Previously Issued HIRF Special Conditions .
Until December 1, 2012, the installation of a level A electrical and electronic system, was allowed under section (d) of the HIRF regulations, if it could be shown the system intended for installation previously complied with HIRF special conditions prescribed under 14 CFR 21.16 and issued before December 1, 2007. This provision was available for a 5-year period. Therefore , section (d) of the HIRF regulations is no longer applicable.
8 MARGINS Margins are not needed if your HIRF compliance is based on tests of the specific aircraft model and system undergoing certification. Margins are also not required if your HIRF compliance is based on analysis or similarity if the process validation is robust and the data well substantiated. Where data ha s limited substantiation, a margin may be needed depending on the available justifications. When a margin is needed, include a justification for the selected margin in the HIRF compliance plan, as discussed in paragraph 9.
9 HIRF COMPLIANCE
9.1 HIRF Compliance Plan.
You should establish an overall compliance plan 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. You should discuss the HIRF compliance plan with, and submit it to, the FAA for approval before ini tiating HIRF compliance activities. If the aircraft, system, or installation design changes after approval, you should submit a revised HIRF compliance plan to the FAA for approval. The HIRF compliance plan should include the following:
• HIRF compliance plan summary;
• Identification of the aircraft systems, with classification based on the safety assessment as it relates to HIRF (see paragraph s 7.2 and 7.3);
• HIRF environment for the aircraft and installed systems; and
• Verification methods, such as test, analysis, or similarity.
9.2 HIRF Verification Test, Analysis, or Similarity Plan.
Test, analysis, and similarity are all acceptable methods for showing HIRF compliance .
The applicant should choose the method most appropriate for its project. See paragraphs 10 and 11 of this AC and SAE ARP5583A, for additional guidance o n selecting the appropriate method. Specific HIRF test, analysis, or similarity plans should be prepared to describe specific verification activities. One or more verifica tion 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.
9.2.1 HIRF Test Plan.
A HIRF compliance test plan should include the equipment, system, and aircraft test objectives for the acquisition of data to support HIRF compliance verification. The test plan should provide an overview of the factors being addressed for each system test requirement. 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. The test plan should include:
• Purpose of the test;
• Description of the aircraft and/or system being tested;
• System configuration drawings;
• Proposed test setup and methods;
• Intended test levels, modulations, and frequency bands;
• Pass/fail criteria; and
• Test schedule and test location.
The test plan should cover HCL A, B, and C systems and equipment, as appropriate.
HCL A systems may need both laboratory integrated systems tests and aircraft tests.
HCL B and C systems and equipment need only equipment laboratory testing.
9.2.2 Analysis Plan.
A HIRF compliance analysis plan should include the objectives, both at the system and equipment level, for generating data to support HIRF compliance verification.
Comprehensive modeling and analysis for RF field coupling to aircraft systems and structures is an emerging technology; therefore, the analysis plan should be coordinated with the FAA to determine an acceptable scope for the analysis. The ana lysis plan should include:
• Purpose and scope of the analysis;
• Description of the aircraft and/or system addressed by the analysis;
• System configuration descriptions;
• Proposed analysis methods;
• Approach for validating the analysis results;
• Pass/fail criteria; and
• Margins (if necessary).
Note: When data have limited substantiation, the analysis plan should also include a description and justification for margins to account for analysis uncertainty. See paragraph 8 for additional information on margins.
9.2.3 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 program. The similarity plan should include:
• Purpose and scope of the similarity assessment;
• Specific systems addressed by the similarity assessment;
• Data used from the previously certified systems, equipment, and aircraft;
• Details on differences between the aircraft and system being certified and the similar aircraft and system from which the data will be used; and
• Margins (if necessary).
Note: When data have limited substantiation, the similarity plan should also include a description and justification for margins to account for similarity uncertainty. See paragraph 8 for additional information on margins.
9.3 Compliance Reports.
One or more compliance reports may be necessary to document the results of your 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 programs, a compliance summary report may be useful to summarize the results of tests and analysis. For HIRF certification programs of relatively simple systems, a single compliance report is adequate.
9.3.1 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 noncompliance with HIRF requirements, actions taken to correct the noncompliance, and any similarity declarations. You should also provide supporting rationale for any deviations from system performance observed during testing.
9.3.2 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. If applicable, these reports should identify any modeling uncertainty and verify that the margins established in the analysis plan were met.
9.3.3 Similarity Reports.
Similarity reports should document the significant aircraft, system, equipment, and installation features common between the aircraft or system that is the subject of the similarity analysis and the aircraft or system that previously was certified for HIRF. You should identify all significant differences encountered, along with the assessment of the impact of these differences on HIRF compliance. If applicable, these reports should identify any similarity uncertainty and verify that the margins established in the similarity plan were met.
9.4 Methods of Compliance Verification.
9.4.1 Various methods are available to aid in demonstrating HIRF compliance. Paragraphs 10 and 11 of this AC describe methods acceptable to the FAA . Figures 1 and 2 below outline the steps to HIRF compliance for systems requiring System HCL A. Figure 3 below outlines the steps to HIRF compliance for systems requiring System HCL B or C.
The steps in these figures are not necessarily accomplished seque ntially. Wherever a decision point is indicated on these figures, you should complete the steps in that path as described in paragraphs 10 and 11 of this AC.
9.4.2 You may use other HIRF compliance techniques to demonstrate system performance in the HIRF environment. However, the FAA should approve those techniques before you use them.