AMC 20-136A Aircraft Electrical and Electronic System Lightning Protection

• ED Decision 2022/001/R found in: EAR for AMC for Airworthiness of Products, Parts and Appliances (AMC-20) (Amendment 23)

AMC 20-136AAircraft Electrical and Electronic System Lightning Protection ED Decision 2022/001/R 1. PURPOSE a. This AMC d escribes an acceptable means, but not the only means, for demonstrating compliance with the applicable certification specifications (CSs) related to system lightning protection (CS 23.1306/2515, CS25.1316, CS 27.1316, and CS 29.1316). 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 th is AMC to indicate that an action is recommended but is not necessary to demonstrate compliance with the applicable CS s when using this AMC. c. Appendix 1 addresses definitions and acronyms. Appendix 2 contains examples. 2. SCOPE AND APPLICABILITY a. This AMC provides possible means to demonstrate compliance with CS 23.1306/2515, 25.1316, 27.1316, and 29.1316 for the effects on electrical and electronic systems due to lightning transients induced or conducted onto equipment and wiring. 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 CS s. Note : For CS-23 Amendment 5 and higher, there is a new specification, i.e. CS 23.2515, which is similar to CS 23.1306. The associated AMC for CS 23.2515 is published separately in the AMC & GM to CS-23, based on ASTM F3061/F3061M-17. The present AMC 20-136A can still be used as guidance for CS 23.2515, which would be acceptable as equivalent means of compliance as AMC/GM CS-23. b. Applicants must also comply with CS 23.1306/2515, 25.1316, 27.1316, and 29.1316 for the effects on aircraft electrical and electronic systems when lightning directly attaches to equipment, components, or wiring. This AMC addresses the functional aspects of these effects on aircraft electrical and electronic equipment, components, or wiring. However, this AMC does not address lightning effects such as burning, eroding, and blasting of aircraft equipment, components, or wiring. Compliance for these effects is demonstrated by meeting the applicable CS 23.867/2335, 25.581, 27.610, 27.865, 29.610, and 29.865 and following the associated AMC. c. For information on fuel ignition hazards due to lightning, see AMC 25.954, Fuel System Lightning Protection , FAA ACs 20-53C, Protection of Aircraft Fuel Systems Against Fuel Vapor Ignition Caused By Lightning , and 25.954-1, Transport Airplane Fuel System Lightning Protection . d. This AMC does not address lightning zoning methods, lightning environment definition, or lightning test methods. For information on these topics, appropriate EUROCAE/SAE guidance material can be used. For information on f uel s tructural l ightning p rotection, see EUROCAE policy ER-002 and ER-006. 3. DOCUMENT HISTORY This AMC supersedes AMC 20-136 , Aircraft Electrical and Electronic System Lightning 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 23.867/2335, 23.901/2400, 23.954/2430, 23.1301/2500, 23.1306/2515, 23.1309/2510, 23.1529/2625 ; 2. CS 25.581, 25.901, 25.954, 25.1301, 25.1309, 25.1316, 25.1529, 25.1705 ; 3. CS 27.610, 27.901, 27.954, 27.1301, 27.1309, 27.1316, 27.1529 ; and 4. CS 29.610, 29.901, 29.954, 29.1301, 29.1309, 29.1316, 29.1529. EASA Certification Specifications (CSs) and Acceptable Means of Compliance (AMC) may be downloaded from the EASA website at www.easa.europa.eu . b. FAA Advisory Circulars (ACs) and (c) any corrective actions required by the flight crew during or after occurrence of a l ightning - related failure. 2. Lightning safety assessment . A safety assessment related to lightning must be performed to establish and classify the equipment or system failure conditions. Table 1 provides 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 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 lightning regulations. Based on the safety classification of the failure condition established by the safety assessment, the systems should be assigned appropriate system LCLs, as shown in Table 1. The lightning safety assessment should consider the common - cause effects of lightning, particularly for highly integrated systems and systems with redundant elements. The lightning safety assessment determines the consequences of failures for the aircraft functions that are performed by the system. The system LCL classification assigned to the systems and functions can be different from the d evelopment a ssurance l evel (DAL) (ED-79A/ARP 4754A) / d esign a ssurance l evel (DAL) (ED 80/DO-254 , ED-12C/DO-178C ) assigned for equipment redundancy, software, and airborne electronic hardware (AEH). This is because lightning is an environment that can cause common - cause effects. The term ‘design assurance level’ or ‘ development assurance level’ ( both abbreviated to ‘ DAL ’ ) should not be used to describe the system LCL because of the potential differences in the assigned classifications for software, AEH, and equipment redundancy. The lightning safety assessment must include all electrical and electronic equipment, components and electrical interconnections, assuming 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 an information input to the lightning safety assessment. This information should only be used in the next phase, to show compliance with the applicable subpart of the lightning regulation, after the required LCL for the system is defined by the lightning safety assessment. The lightning safety assessment results from inputs coordinated between the safety specialist, the system specialist, and the HIRF/ l ightning specialist. This process may vary from applicant to applicant. Further details on performing the safety assessment can be found in AC 23.1309-1E, AMC 25.1309, AC-27-1B, AC-29-2C, EUROCAE ED 79A, SAE ARP 4761, and EUROCAE ED-158. N ote : Considering that lightning and HIRF environments may have similar effects on electro electronic systems (disturbing electrical signals, causing upsets or damage to circuits) and that the applicable regulations are similarly structured, in many cases the system LCL and corresponding HIRF c ertification l evel (see AMC 20-158A ) should be the same. Table 1: Indirect effect of lightning most severe failure conditions of the function and system lightning certification levels | LIGHTNING REQUIREMENTS EXCERPTS FROM CS23.1306/2515, CS 25.1316, CS 27.1316, AND CS29.1316 | | MOST SEVERE FAILURE CONDITION OF THE FUNCTION | | SYSTEM LIGHTNINGCERTIFICATION LEVEL (LCL) | | --- | --- | --- | --- | --- | | | | | | | | | | | | | | | | | | | | | | | | | | (a)Each electrical and electronic system that performs a function whose failure would prevent the continued safe flight and landing of the aircraft. | | | | | | | | Catastrophic | | A | | | | | | | | | | | | | | | | | | | EASA Certification Specifications (CSs) and Acceptable Means of Compliance (AMC) may be downloaded from the EASA website at www.easa.europa.eu . b. FAA Advisory Circulars (ACs) 1. AC 20-155, SAE Documents to Support Aircraft Lightning Protection Certification 2. AC 21-16, RTCA Document DO-160 Versions D, E, F, and G, Environmental Conditions and Test Procedures for Airborne Equipment 3. AC 23-17, Systems and Equipment Guide for Certification of Part 23 Airplanes and Airships 4. AC 23.1309-1E, System Safety Analysis and Assessment for Part 23 Airplanes 5. AC 27-1B, Certification of Normal Category Rotorcraft 6. AC 29-2C, Certification of Transport Category Rotorcraft The applicant can view and download copies from the FAA web-based Regulatory and Guidance Library (RGL) at 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/ . c. European Organisation for Civil Aviation Equipment (EUROCAE) 1. EUROCAE ED-79A, Guidelines for Development of Civil Aircraft and Systems 2. EUROCAE ED-14G, Environmental Conditions and Test Procedures for Airborne Equipment 3. EUROCAE ED-84A, Aircraft Lightning Environment and Related Test Waveforms 4. EUROCAE ED-91A, Aircraft Lightning Zoning 5. EUROCAE ED-105A, Aircraft Lightning Test Methods 6. EUROCAE ED-113, Aircraft Lightning Direct Effects Certification 7. EUROCAE ED-158, User Manual for Certification of Aircraft Electrical/Electronic Systems for the Indirect Effects of Lightning 8. EUROCAE ED-234, User Guide Supplement to 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 d. Radio Technical Commission for Aeronautics (RTCA) 1. DO-160, Environmental Conditions and Test Procedures for Airborne Equipment . This document is technically equivalent to EUROCAE ED-14. Anywhere there is a reference to RTCA/DO-160, EUROCAE ED-14 may be used. 2. DO-357, User Guide Supplement to DO-160 . T his document is technically equivalent to EUROCAE ED-234. Anywhere there is a reference to RTCA/DO-357, EUROCAE ED-234 may be used. 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 e. Society of Automotive Engineers (SAE International) 1. SAE Aerospace Recommended Practice (ARP) 4754A, Guidelines for Development of Civil Aircraft and Systems , December 2010. This document is technically equivalent to EUROCAE ED-79A. Anywhere there is a reference to ARP 4754A, EUROCAE ED-79A may be used. 2. SAE ARP 4761, Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment , December 1996. 3. SAE ARP 5412B, Aircraft Lightning Environment and Related Test Waveforms . This document is technically equivalent to EUROCAE ED-84A. Anywhere there is a reference to ARP 5412A, EUROCAE ED-84A may be used. 4. ARP 5414B, Aircraft Lightning Zoning . This document is technically equivalent to EUROCAE ED-91A. Anywhere there is a reference to ARP 5414B, EUROCAE ED-91A may be used. 5. ARP 5415B, User’s Manual for Certification of Aircraft Electrical/Electronic Systems for the Indirect Effects of Lightning . This document is technically equivalent to EUROCAE ED-158. 6. ARP 5416A, Aircraft Lightning Test Methods . This document is technically equivalent to EUROCAE ED-105A. Anywhere there is a reference to ARP 5416A, EUROCAE ED-105A may be used. 6. ARP 5416A, Aircraft Lightning Test Methods . This document is technically equivalent to EUROCAE ED-105A. Anywhere there is a reference to ARP 5416A, EUROCAE ED-105A may be used. 7. ARP 5577, Aircraft Lightning Direct Effects Certification . This document is technically equivalent to EUROCAE ED-113. Anywhere there is a reference to ARP 5577, EUROCAE ED-113 may be used. SAE International documents may be purchased from: SAE Customer Service 400 Commonwealth Drive Warrendale, PA 15096-0001, USA Website: http: //www.sae.org f. ASTM F3061/F3061M-17, Standard Specification for Systems and Equipment in Small Aircraft ASTM documents may be purchased from: ASTM International 100 Barr Harbor Drive PO Box C700 West Conshohocken, PA 19428-2959, USA Website: https: //www.astm.org 5. BACKGROUND a. Regulatory a pplicability . The CS s for aircraft electrical and electronic system lightning protection are based on the aircraft’s potential for lightning exposure and the consequences of system failures. The CSs require lightning protection of aircraft electrical and electronic systems with catastrophic, hazardous, or major failure conditions for aircraft certified under CS 25. The specifications also apply to CS-23 (at Am en d men t 4 or earlier) aeroplanes, and CS-27 and CS-29 rotorcraft approved for operations under instrument flight rules (IFR) . Those CS-23 aeroplanes, and CS-27 and CS-29 rotorcraft approved solely for operations under visual flight rules (VFR) , require lightning protection of electrical and/ or electronic systems that have catastrophic failure conditions. For CS-23 Am en d men t 5, the electrical and electronic systems with catastrophic and hazardous failure conditions must be protected against the effects of lightning where exposure to lightning is likely. b. Regulatory r equirements . Protection against the effects of lightning for aircraft electrical and electronic systems, regardless of whether these are ‘indirect’ or ‘direct’ effects of lightning, is addressed under CS 23.1306/2515, 25.1316, 27.1316, and 29.1316. The terms ‘indirect’ and ‘direct’ are often used to classify the effects of lightning. However, the CS s 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. 6. APPROACHES TO COMPLIANCE a. General . The following activities describe how compliance with CS 23.1306/2515, 25.1316, 27.1316, and 29.1316 may be demonstrated. Adherence to the sequence shown is not necessary. More detailed information on lightning certification compliance is provided in the User ’ s Manual referred to in SAE ARP 5415B / EUROCAE ED-158. The applicant should: 1. identify the systems to be assessed (see Section 6 (c)) ; 2. determine the lightning strike zones for the aircraft (see Section 6 ( d )) ; 3. establish the aircraft lightning environment for each zone (see Section 6 (e)) ; 4. determine the lightning transient environment associated with the systems (see Section 6 ( f )) ; 5. establish e quipment t ransient d esign l evels (ETDLs) and aircraft a ctual t ransient l evels (ATLs) (see Section 6 ( g ) ) ; 6. verify compliance with the applicable requirements (see Section 6 ( h )) ; and 7. take corrective measures (if needed) (see Section 6 ( i ) ). Sections 7 and 8 give more details on these steps for the compliance of Level A systems as well as of Level B and Level C systems respectively. | | | Catastrophic | | A | | | | | | | | | | | | | | | | | | | | (b)Each electrical and electronic system that performs a function, for which failure would reduce the capability of the aircraft or the ability of the flight crew to respond to an adverse operating condition.Note: Requirement applicable for small aircraft and rotorcraft approved for instrument flight rule (IFR) operations | | | | | | | | | | | | | | Hazardous/ Major | | B/C | | | | | | | | | | | | | | | | | | | Sections 7 and 8 give more details on these steps for the compliance of Level A systems as well as of Level B and Level C systems respectively. b. Lightning effect considerations . 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, such as radio antennas and air - data probes. Additional guidance on lightning protection against lightning damage for external equipment and sensor installations can be found in EUROCAE ED-113. Lightning causes voltage and current transients to appear on equipment circuits. Equipment circuit impedances and configurations will determine whether lightning transients are primarily voltage or current. These transient voltages and currents can degrade system performance permanently or temporarily. The two primary types of degradation are component damage and system functional upsets. 1. Component damage This is a permanent condition in which transients alter the electrical characteristics of a circuit. Examples of devices that may be susceptible to component damage include the following : (a) active electronic devices, especially high-frequency transistors, integrated circuits, microwave diodes, and power supply components ; (b) passive electrical and electronic components, especially those of very low power or voltage rating ; (c) electro-explosive devices, such as squibs and detonators ; (d) electromechanical devices, such as indicators, actuators, relays, and motors ; and (e) insulating materials (for example, insulating materials in printed circuit boards and connectors) and electrical connections that can burn or melt. 2. System functional upset (a) Functional upset is mainly a system problem caused by electrical transients. They may permanently or momentarily upset a signal, circuit, or a system component, which can adversely affect system performance enough to compromise flight safety. A functional upset is a change in digital or analogue state that may or may not require a manual reset. In general, functional upset depends on circuit design and operating voltages, signal characteristics and timing, and the system and software configuration. (b) Systems or devices that may be susceptible to functional upsets include computers and data/signal processing systems, electronic engine and flight controls, and power generating and distribution systems. c. Identify the systems to be assessed 1. General . The aircraft systems that require a lightning safety assessment should be identified. 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 points address any system failure that may cause or contribute to an effect on the safety of flight of an aircraft. The effects of a lightning 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 the following : (a) all normal aircraft operating modes, phases of flight, and operating conditions; (b) all lightning - related failure conditions and their subsequent effects on aircraft operations and the flight crew; and (c) any corrective actions required by the flight crew during or after occurrence of a l ightning - related failure.