U.S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: Aircraft Electrical and Electronic Date: AC No: 20-136C System Lightning Protection Initiated By: AIR-626 This advisory circular (AC) provides you, the applicant, with information and guidance on how you can protect aircraft electrical and electronic systems from the effects of lightning. This AC describes a means, but not the only means, for you to demonstrate compliance with title 14, Code of Federal Regulations (14 CFR) 23.1306 (amendment 23-61), 23.2515, 25.1316, 27.1316, and 29.1316, Electrical and electronic system lightning protection, as they pertain to the type or supplemental type certification of your aircraft.
If you have suggestions for improving this AC, you may use the Advisory Circular Feedback Form at the end of this AC.
Daniel J. Elgas Aviation Safety Director, Policy and Standards, Division Aircraft Certification Service
AC 20-136C Table of Contents Paragraph Page
1 Purpose1
2 Applicability1
3 Cancellation2
4 Scope2
5 Related Material2
6 Background7
7 Steps for Showing Compliance7
8 Lightning Compliance16
9 Effects of Transients20
10 Steps to LCL A System Lightning Compliance21
11 Steps to LCL B And C System Lightning Compliance32
12 Maintenance, Protection Assurance, and Modifications36
Appendix A. DefinitionsA-1
Appendix B. AcronymsB-1
Appendix C. Examples of Lightning Safety Assessment Considerations - LCL A
Systems on Transport Category AirplanesC-1
ii
AC 20-136C TABLES Number Page T
able 1. Lightning Failure Conditions and Certification Levels10
Table 2. Lightning Failure Conditions and Certification Levels (§ 23.2515)11
Table 3. Items Recommended for a Lightning Certification Plan16
Table 4. Equipment Transient Design Level - LCL A Displays29
FIGURES Number Page
Figure 1. Relationships Among Transient Levels14
Figure 2. Typical Compliance Process for LCL A Systems22
Figure 3. Typical Compliance Process for LCL B and C Systems33
iii
AC 20-136C 1 PURPOSE.
1.1 This AC provides you, the applicant, with information and guidance on how you can protect aircraft electrical and electronic systems from the effects of lightning. This AC describes a means, but not the only means, for you to demonstrate compliance with 14 CFR 23.1306 (amendment 23-61), 23.2515, 25.1316, 27.1316, or 29.1316, Electrical and electronic system lightning protection, as they pertain to the type or supplemental type certification of your aircraft.
1.2 This revision incorporates the guidance in the Federal Aviation Administration (FAA) Policy Statement PS-ACE-23-10(), HIRF/Lightning Test Levels and Compliance Methods for 14 CFR Part 23 Class I, II, and III Airplanes. This policy describes an acceptable means to demonstrate compliance with § 23.1306 (amendment 23-61) or § 23.2515. The applicant may also use a means of compliance, which may include consensus standards, accepted by the Administrator under § 23.2010.
Note: FAA accepted means of compliance based on ASTM consensus standards for 14 CFR part 23 airplanes, including any required changes for acceptance, are available at the FAA Small Airplanes Design Approvals website. Reference “Industry Standards.”
2 APPLICABILITY.
2.1 The guidance provided in this AC is for those seeking a new Type Certificate (TC) or a change to an existing TC when the certification basis requires you to address the certification requirements of §§ 23.1306 (amendment 23-61), 23.2515, 25.1316,
27.1316, or § 29.1316.
2.2 This is a guidance document. Its content is not legally binding in its own right and will not be relied upon by the Department as a separate basis for affirmative enforcement action or other administrative penalty. Conformity with the guidance document is voluntary only. Nonconformity will not affect rights and obligations under existing statutes and regulations.
2.3 The FAA will consider other means of demonstrating compliance that an applicant may elect to present. Terms such as “should,” “may,” and “must”, as used in this AC, only refer to actions necessary to follow this particular means of compliance. If the FAA becomes aware of circumstances in which following this AC would not result in compliance with the applicable regulations, the FAA may require additional substantiation or design changes as a basis for finding compliance.
2.4 The material contained in this AC does not change or create any additional regulatory requirement, nor does it authorize changes in, or permit deviations from, existing regulatory requirements.
AC 20-136C 3 CANCEL LATI ON.
This AC cancels AC 20-136B, Aircraft Electrical and Electronic System Lightning Protection, dated September 7, 2011.
4 SCOPE.
4.1 This AC provides guidance on complying with §§ 23.1306 (amendment 23-61),
23.2515, 25.1316, 27.1316, and 29.1316 for the effects on electrical and electronic systems when lightning currents are induced or conducted onto equipment, components, or wiring. This AC addresses the functional aspects of these effects for aircraft electrical and electronic equipment, components, or wiring. However, this AC does not address lightning effects such as burning, eroding, and blasting of aircraft equipment, components, or wiring. For guidance on mitigating those lightning effects, applicants may refer to SAE ARP5577, Aircraft Lightning Direct Effects Certification.
4.2 For information on fuel ignition hazards, see AC 20-53, Protection of Aircraft Fuel Systems Against Fuel Vapor Ignition Caused by Lightning and AC 25.954-1, Transport Airplane Fuel System Lightning Protection. This AC does not address lightning zoning methods, lightning environment definition, or lightning test methods. For information on lightning zoning methods and lightning environment definition, see AC 20-155, Industry Documents To Support Aircraft Lightning Protection Certification. For information on lightning test methods, see SAE ARP5416, Aircraft Lightning Test Methods, or RTCA/DO-160, Section 22, Lightning Induced Transient Susceptibility, and Section 23, Lightning Direct Effects.
Note: When complying with §§ 23.1306 (amendment 23-61), 23.2515, 25.1316,
27.1316, and 29.1316, applicants may use RTCA/DO-160D, Change Notice 3, or later FAA accepted revisions.
5 RELATED MATERIAL.
5.1 Title 14, Code of Federal Regulations (14 CFR).
The following regulations are related to this AC. You can download the full text of these regulations at the e-CFR website. You can order a paper copy by sending a request to the U.S. Superintendent of Documents, U.S. Government Publishing Office, Washington, D.C. 20402-0001; by calling telephone number (202) 512-1800; or by sending a request by facsimile to (202) 512-2250.
5.1.1 Part 23, Airworthiness Standards: Normal Category Airplanes:
• § 23.867, Electrical bonding and protection against lightning and static electricity.
• § 23.901, Installation.
• § 23.954, Fuel system lightning protection.
• § 23.1301, Function and installation.
AC 20-136C
• § 23.1306, a me ndment 23-61, Electrical and electronic system lightning protection .
• § 23.1309, Equipment, systems, and installations.
• § 23.1529, Instructions for continued airworthiness.
• § 23.2335, Lightning protection.
• § 23.2400, Powerplant installation.
• § 23.2430, Fuel systems.
• § 23.2500, Airplane level systems requirements.
• § 23.2505, Function and installation.
• § 23.2510, Equipment, systems, and installations.
• § 23.2515, amendment 23-64 or later, Electrical and electronic system lightning protection.
5.1.2 Part 25, Airworthiness Standards: Transport Category Airplanes:
• § 25.581, Lightning protection.
• § 25.901, Installation.
• § 25.954, Fuel system lightning protection.
• § 25.1301, Function and installation.
• § 25.1309, Equipment, systems, and installations.
• § 25.1316, Electrical and electronic system lightning protection.
• § 25.1529, Instructions for continued airworthiness.
• § 25.1705, Systems and functions: EWIS (Electrical Wiring Interconnection Systems).
5.1.3 Part 27, Airworthiness Standards: Normal Category Rotorcraft:
• § 27.610, Lightning and static electricity protection.
• § 27.865, External loads.
• § 27.901, Installation.
• § 27.954, Fuel system lightning protection.
• § 27.1301, Function and installation.
• § 27.1309, Equipment, systems, and installations.
• § 27.1316, Electrical and electronic system lightning protection.
• § 27.1529, Instructions for continued airworthiness.
5.1.4 Part 29, Airworthiness Standards: Transport Category Rotorcraft:
AC 20-136C
• § 29.610, L ight ning and static electricity protection.
• § 29.865, External loads.
• § 29.901, Installation.
• § 29.954, Fuel system lightning protection.
• § 29.1301, Function and installation.
• § 29.1309, Equipment, systems, and installations.
• § 29.1316, Electrical and electronic system lightning protection.
• § 29.1529, Instructions for Continued Airworthiness.
5.1.5 Part 33, Airworthiness Standards: Aircraft Engines:
• § 33.28, Engine control systems.
• § 33.53, Engine system and component tests (Reciprocating aircraft engines).
• § 33.91, Engine system and component tests (Turbine aircraft engines).
5.1.6 Part 35, Airworthiness Standards: Propellers:
• § 35.23, Propeller control system.
• § 35.38, Lightning strike.
5.2 European Union Aviation Safety Agency (EASA) Certification Specifications.
You can get copies of these documents from the European Union Aviation Safety Agency by mail at Postfach 10 12 53, D-50452 Cologne, Germany; telephone +49 221 8999 000; fax: +49 221 8999 099; or on the EASA website.
• Certification Specifications (CS)-23, Normal-Category Aeroplanes
• CS-25, Large Aeroplanes.
• CS-27, Small Rotorcraft.
• CS-29, Large Rotorcraft.
5.3 FAA Advisory Circulars.
The following FAA ACs are related to the guidance in this AC. You should refer to the latest versions for guidance, which are available on the FAA Advisory Circulars website and the Dynamic Regulatory System.
• AC 20-155, Industry Documents to Support Aircraft Lightning Protection Certification.
• AC 21-16, RTCA Document DO-160 Versions D, E, F, and G, Environmental Conditions and Test Procedures for Airborne Equipment.
• AC 23-17, Systems and Equipment Guide for Certification of Part 23 Airplanes and Airships.
AC 20-136C
• AC 23.1309 -1, System Safety Analysis and Assessment for Part 23 Airplanes.
• AC 25.1309-1, System Design and Analysis.
• AC 27-1, Certification of Normal Category Rotorcraft.
• AC 29-2, Certification of Transport Category Rotorcraft.
• AC 33.28-3, Guidance Material for 14 CFR 33.28, Engine Control Systems.
• AC 35.23-1, Guidance Material for 14 CFR 35.23, Propeller Control System.
5.4 FAA Policy Statement.
The following FAA policy statement is related to the guidance in this AC, which is available on the Dynamic Regulatory System (DRS) website. If the policy statement is revised after publication of this AC, you should refer to the latest version for guidance.
• PS-ACE-23-10, HIRF/Lightning Test Levels and Compliance Methods for 14 CFR Part 23 Class I, II, and III Airplanes.
5.5 FAA Technical Report.
The following FAA technical report is related to the guidance in this AC, which is available on the FAA William J. Hughes Technical Center website. If the technical report is revised after publication of this AC, you should refer to the latest version for guidance. On the website, select “Search Library Catalog” and enter report number DOT/FAA/TC-22/11, Lightning Protection of Aircraft Handbook.
5.6 Industry Documents.
Note: The industry documents cited in this section refer to the current edition or the FAA accepted revision(s).
5.6.1 Industry Consensus Standards.
FAA accepted means of compliance based on ASTM consensus standards for part 23 airplanes, including any required changes for acceptance, are available at the FAA Small Airplanes Design Approvals website (reference “Industry Standards”).
• FAA Accepted Means of Compliance for Part 23 Airplanes (Pre-Amendment 23-64)
• FAA Accepted Means of Compliance for Part 23 Airplanes (Amendment 23-64 or later)
5.6.2 European Organization for Civil Aviation Equipment (EUROCAE).
The following EUROCAE documents are related to the guidance in this AC, which are available on the EUROCAE website. If the documents are revised after publication of this AC, you should verify that the FAA accepts the latest version as guidance.
• EUROCAE ED-14, Environmental Conditions and Test Procedures for Airborne Equipment.
• EUROCAE ED-84, Aircraft Lightning Environment and Related Test Waveforms.
AC 20-136C
• EURO CAE ED-91, Aircraft Lightning Zoning.
• EURO CAE ED-105, Aircraft Lightning Test Methods.
• EUROCAE ED-113, Aircraft Lightning Direct Effects Certification.
• EUROCAE ED-158, User’s Manual for Certification of Aircraft Electrical/Electronic Systems for the Indirect Effects of Lightning.
• EUROCAE ED-303, User’s Guide for Lightning Protection of Fuel Tank Structure and Systems.
5.6.3 RTCA, Inc.
The following RTCA document is related to the guidance in this AC, which can be ordered on the RTCA website. If the document is revised after publication of this AC, you should verify the FAA accepts the latest version for guidance.
• RTCA/DO-160, Environmental Conditions and Test Procedures for Airborne Equipment.
Note 1: This document is technically equivalent to EUROCAE ED-14. Anywhere there is a reference to RTCA/DO-160, EUROCAE ED-14 may be used.
Note 2: You may use RTCA/DO-160D, Change Notice 3, or later FAA accepted revisions.
5.6.4 Society of Automotive Engineers (SAE) International.
The following SAE documents are related to the guidance in this AC, which are available on the SAE website. If the documents are revised after publication of this AC, you should verify the FAA accepts the latest version for guidance.
• Aerospace Recommended Practice (ARP) 4754, Guidelines for Development of Civil Aircraft and Systems.
• ARP4761, Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment.
• ARP5412, Aircraft Lightning Environment and Related Test Waveforms.
• ARP5414, Aircraft Lightning Zoning.
• ARP5415, User’s Manual for Certification of Aircraft Electrical/Electronic Systems for the Indirect Effects of Lightning.
Note: Anywhere there is a reference to ARP5415, EUROCAE ED-158 may be used.
• ARP5416, Aircraft Lightning Test Methods. This document is technically equivalent to EUROCAE ED-105.
Note: Anywhere there is a reference to ARP5416, EUROCAE ED-105 may be used.
• ARP5577, Aircraft Lightning Direct Effects Certification.
• ARP6205, Transport Airplane Fuel System Lightning Protection.
AC 20-136C 6 BACK GR OUND.
6.1 Regulatory Applicability.
The standards for aircraft electrical and electronic system lightning protection are based on the aircraft's potential for lightning exposure and the consequences of system failure.
The regulations require lightning protection of aircraft electrical and electronic systems with catastrophic, hazardous, or major failure conditions for aircraft certificated under 14 CFR parts 25, 27 and 29. The requirements also apply to 14 CFR part 23 airplanes approved for operations under instrument flight rules (IFR). Those part 23 (amendment 23-61) airplanes and part 27 rotorcraft, approved solely for operations under visual flight rules (VFR), require lightning protection of electrical or electronic systems that have catastrophic failure conditions.
6.2 Regulatory Requirements.
Protection against the effects of lightning for aircraft electrical and electronic systems, regardless of whether these are ‘indirect’ or ‘direct’ effects of lightning, are addressed under §§ 23.1306 (amendment 23-61), 23.2515, 25.1316, 27.1316, and 29.1316. The terms ‘indirect’ and ‘direct’ are often used to classify the effects of lightning; however, the regulations do not, and are not intended to, differentiate between the effects of lightning. The focus is to protect aircraft electrical and electronic systems from the effects of lightning.
7 STEPS FOR SHOWING COMPLIANCE.
7.1 General.
7.1.1 The following steps describe a method for complying with §§ 23.1306 (amendment 23-
61) 23.2515, 25.1316, 27.1316, and 29.1316 requirements for your aircraft’s electrical and electronic systems. Adherence to the order of activities in the list below is not required.
• Identify the systems to be assessed.
• Perform a lightning safety assessment.
• Determine the lightning strike zones for the aircraft.
• Establish the aircraft lightning environment for each zone.
• Determine the lightning transient environment associated with the systems.
• Establish equipment transient design levels (ETDLs) and aircraft actual transient levels (ATLs).
• Verify compliance with the requirements.
• Take corrective measures, if needed.
Note: The steps above should be performed to address lightning transients induced in electrical and electronic system wiring and equipment, and lightning damage to aircraft external equipment and sensors that are connected to electrical and electronic systems, 7
AC 20-136C such as radio antennas and air data probes. More detailed guidance on lightning protec tion of systems is provided in SAE ARP5415 / EUROCAE ED-158. Additional guidance on lightning protection against lightning damage for external equipment and sensor installations can be found in SAE ARP5577.
7.2 Identify the Systems to be Assessed.
7.2.1 The aircraft systems requiring a lightning safety assessment should be identified.
Address any electrical or electronic system failure that may cause or contribute to an adverse effect on the aircraft (catastrophic, hazardous, or major failure condition). The effects of a lightning strike, therefore, should be assessed in a manner that allows for the determination of the degree to which the aircraft’s and/or its systems’ safety may be influenced. The lightning safety assessment should cover:
• All normal aircraft operating modes, phases of flight, and operating conditions; and
• All lightning-related failure conditions and their subsequent effect on aircraft operations and the flightcrew.
• System responses and any required flightcrew actions.
7.3 Lightning Safety Assessment.
7.3.1 A safety assessment related to lightning effects should be performed to establish and classify the system failure conditions. Tables 1 and 2 provide the corresponding failure condition classification and system lightning certification level (LCL) for the appropriate lightning regulations. The failure condition classifications and terms used in this AC are consistent with 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 lightning regulations. Based on the failure condition classification established by the safety assessment, the systems should be assigned appropriate LCLs, as shown in Tables 1 and 2. The lightning safety assessment should consider the common cause1 effects of lightning, particularly for highly integrated systems and systems with redundant elements. Common cause effects due to lightning exposure may simultaneously have an adverse impact on multiple electrical and electronic systems’ functions. The lightning safety assessment determines the consequences of failures for the aircraft functions that the systems perform.
7.3.2 The LCL classification assigned to the system and functions may be different from the development assurance level assigned for equipment redundancy, software, and airborne electronic hardware. This is because the lightning environment may lead to common cause effects. The term “development assurance level” should not be used to describe the LCL because of the potential differences in assigned classifications for software, airborne electronic hardware, and equipment redundancy. The lightning safety
1 Reference ACs 23.1309-1, 25.1309-1, 27-1, or 29-2 for common cause considerations and analysis.
AC 20-136C assessment should include all electrical and electronic equipment, components, and ele ctrical interconnections, and should assume that they are potentially affected by lightning. It is not appropriate to use the lightning immunity data for electrical and electronic equipment, components, and electrical interconnections as information input to the lightning safety assessment. Lightning immunity should only be used to demonstrate compliance with the applicable paragraph of the lightning regulations, after the required LCL for the system and functions are determined by lightning safety assessment.
7.3.3 The lightning safety assessment should have input from and be coordinated between the applicant’s safety specialists, system specialists, and lightning specialists. This process may vary from applicant to applicant. Further guidance on performing a safety assessment can be found in AC 23.1309-1, AC 25.1309-1, AC 27-1, AC 29-2, SAE ARP4754, and ARP4761. More detailed guidance on the lightning safety assessment is provided in SAE ARP5415 / EUROCAE ED-158.
Note: Considering that lightning and HIRF environments may have similar effects on electronic systems (disturbing electrical signals causing upsets or damage to circuits) and that the regulations are similarly structured, the system LCL and HIRF certification level (HCL) may be the same.