AC 20-136C Figure 2. Typical Compliance Process for LCL A Systems Identify LCLA Systems • Lightning Zones Deterine Aircraft Determine Aircraft- Specific Lightning Environment → System Lightning Define Airoraft and Protection
(1) Features (2) Aircraft-Level System-Level Verification Verification {7] Select Airoraft- Establish System Verification ETDLS Method LOLA Displays Only (3
(4) Verify Aircraft ATL Verify Aircraft ATL Select ETDL by Test by Similarity Verification
(10) Method Verify Aircraft ATL by Analysis Displays Transient Select LCLA evels Qualification Tests Verify ETDLs by System System Similarity Verify ETDLs by
(5) Compare Aircraft ATLs and System ETDLs
(12) Modify Aircraft or Margin System Lightning
(n) = Step number as described Acceptable? Protection in paragraph 10 of this AC (13) Lightning Compliance Demonstrated 22
AC 20-136C
10.1.3 Some systems include mechanical, hydraulic, and/or pneumatic channels as well as e lectrical and electronic channels that perform functions whose failure is catastrophic (would prevent continued safe flight and landing). The lightning safety assessment for §§ 23.1306(a) (amendment 23-61), 23.2515(a), 25.1316(a), 27.1316(a), or § 29.1316(a) only applies to functions performed by electrical and electronic systems. However, you should verify the assumptions made for mechanical, hydraulic, and/or pneumatic channel(s) and consider any influence on whether the electrical/electronic or mechanical channel is in fact the active channel during normal operation. The lightning safety assessment should consider electrical or electronic failures that would adversely affect the function of the mechanical, hydraulic, and/or pneumatic channels. If electrical or electronic equipment, components, and electrical interconnections are used to assist, augment, or monitor for control loop feedback the mechanical, hydraulic, and/or pneumatic channels in performing functions with failures that would prevent continued safe flight and landing during normal operation, then the electrical and electronic channel(s) must comply with §§ 23.1306(a) (amendment 23-61), 23.2515(a),
25.1316(a), 27.1316(a), or § 29.1316(a).
10.1.4 Sections 23.1306(a) (amendment 23-61), 23.2515(a), 25.1316(a), 27.1316(a), and
29.1316(a) do not require you to assume preexisting failure conditions when classifying the functional failure conditions and the scope of the LCL A systems. You should consider total losses, partial losses, and malfunctions of the systems, including hazardously misleading information presented to the flightcrew during and after the aircraft is exposed to lightning.
10.1.5 Sections 23.1306(a)(2) (amendment 23-61), 25.1316(a)(2), 27.1316(a)(2), and
29.1316(a)(2) require that the LCL A systems automatically recover normal operation of the Level A function in a timely manner after exposure to lightning. Section
23.2515(a)(2) requires that the LCL A systems recover normal operation of the Level A function in a timely manner after exposure to lightning unless the recovery conflicts with other operational or functional requirements of the system. Automatic or manual recovery applies to all redundant active channels of the LCL A system required for normal operation. The exception for recovery conflicts should be based on aircraft operational or functional requirements independent of lightning exposure. The exception should not be a mitigation for LCL A system effects observed after exposure to lightning.
10.1.6 Appendix C, Examples of Lightning Safety Assessment Considerations - LCL A Systems on Transport Airplanes, provides examples of system scope for transport category airplanes based on the guidance above. The lightning safety assessment examples for LCL A systems contained in appendix C may also be applicable to normal category airplanes and rotorcraft.
10.2 Step 2 – Define Aircraft and System Lightning Protection Features.
Define the lightning protection features to be incorporated into the aircraft and system designs based on the lightning environments that are applicable to your aircraft and its LCL A systems. Equipment, system, and aircraft lightning protection design may occur before you perform aircraft-level tests and before you determine the actual internal 23
AC 20-136C lightning environment. Therefore, y ou should base the equipment, system, and aircraft lightning protection design on an estimate of the expected internal lightning environment.
10.3 Step 3 – Establish System ETDLs.
Establish the aircraft systems ETDLs from an evaluation of expected lightning transient amplitudes and waveforms for the system installation, structure, and wiring configuration on a specific aircraft. You should establish ETDLs that exceed the ATLs by an acceptable margin as discussed in paragraph 10.12 of this AC. In general, the ETDLs for equipment in a complex system will not be the same for all wire bundles connecting them to other equipment in the system. You may use the results of lightning tests on existing similar aircraft, engineering analyses, or knowledgeable estimates to establish appropriate system ETDLs. While specific aircraft configurations and system installations may lead to ETDLs that have amplitudes and waveforms different than those defined in RTCA/DO-160 section 22, ETDLs are often specified using the information from section 22. The ETDLs must exceed the ATLs by an acceptable margin.
10.4 Step 4 – Select the ETDL Verification Method.
Determine whether to perform system qualification tests on the LCL A system or whether to base the system verification on previous system qualification tests performed on a similar system.
10.5 Step 5 – Verify System ETDLs Using System Qualification Tests.
10.5.1 Lightning-induced transient susceptibility laboratory tests (damage tolerance and functional upset) of RTCA/DO-160, section 22, may be used to build confidence in the equipment’s lightning immunity before conducting laboratory integrated system tests.
Equipment tests may be used to augment the integrated system lightning tests where appropriate. For equipment whose lightning immunity is evaluated as part of the integrated system-level qualification tests, the individual equipment’s lightning testing described in this step is optional.
10.5.2 For the integrated system test of an engine control system, you should also refer to the guidance provided in AC 33.28-3. When the engine certification occurs prior to a known specific aircraft installation, the engine manufacturer should make reasonable installation assumptions for engine-to-aircraft electrical interfaces. The engine installation manual or operating instructions should specify wire characteristics, shielding, connector types, shield terminations, and electrical bonding features for lightning protection that are required when the engine is installed. Systems that are part of the engine certification must be installed in accordance with the engine manufacturer’s requirements. The applicant should perform the required lightning tests with the same wiring, shielding, and electrical bonding configuration as specified in the engine installation manual or operating instructions.
10.5.3 You should identify the equipment, components, sensors, power systems, and wiring associated with the LCL A system undergoing ETDL verification tests, specifically 24
AC 20-136C co nsidering the system functions whose failures are catastrophic. Fo r complex LCL A systems, the system configuration may include redundant equipment, multiple power sources, multiple sensors and actuators, and complex wire bundles. Define the system configuration (including airborne electronic hardware and software) used for the ETDL verification tests. You should obtain the cognizant certification branch’s approval of your system configuration for ETDL verification tests.
10.5.4 If the LCL A system consists of multiple similar channels, you may propose using one or more channels in the laboratory test setup for the integrated system instead of using all similar channels. You should demonstrate that the laboratory test setup adequately performs the intended functions to demonstrate compliance with §§ 23.1306(a) (amendment 23-61), 23.2515(a), 25.1316(a), 27.1316(a), or § 29.1316(a). Ensure that the laboratory test setup represents and monitors any cross-channel interactions, such as cross-channel data links, redundancy management, and system health monitoring.
Note: If pin programming or software is used to identify or configure equipment of similar channels, you should assess whether these differences impact the functions performed.
10.5.5 You should verify the ETDLs using single stroke, multiple stroke, and multiple burst tests on the system wire bundles. Use waveform sets and test levels for the defined ETDLs. Demonstrate that the system operates within the defined pass/fail criteria during these tests. No equipment damage should occur during these system tests or during single stroke pin injection tests using the defined ETDLs. RTCA/DO-160, section 22, provides acceptable test procedures and waveform set definitions. In addition, SAE ARP5416 provides acceptable test methods for complex and integrated systems.
10.5.6 You should evaluate any system effects observed during the qualification tests to ensure they do not adversely affect the system’s continued performance. The LCL A system performance should be evaluated for functions of which failures or malfunctions are catastrophic (would prevent the continued safe flight and landing of the aircraft). Other functions performed by the system of which failures or malfunctions are hazardous or major (would reduce the capability of the aircraft or the ability of the flightcrew to respond to an adverse operating condition) should be evaluated using the guidance in paragraph 11. You should obtain the cognizant certification branch’s approval of your evaluation.
10.6 Step 6 – Verify System ETDLs Using Existing System Data (Similarity).
10.6.1 You may base your ETDL verification on similarity to previously-certified systems without performing more tests. You may do this when:
• There are only minor differences between the previously certified system and installation, and the system and installation to be certified;
• There are no unresolved in-service system problems related to lightning strikes on the previously certified system; and 25
AC 20-136C
• The previously certified system ETDLs were verified by qualification t ests.
10.6.2 To use similarity to previously certified systems, you should assess differences between the previously certified system and installation, and the system and installation to be certified that can adversely affect the system susceptibility. The assessment should cover—
• System interface circuits;
• Wire size, routing, arrangement (parallel or twisted wires), connector types, wire shields, and shield terminations;
• Lightning protection devices such as transient suppressors and lightning arrestors;
• Grounding and bonding; and
• System software and airborne electronic hardware.
10.6.3 If you are unsure how the differences will affect the systems and installations, you should perform more tests and analyses to resolve the open issues.
10.6.4 You should assess every system, even if it uses equipment and installation techniques that have previous certification approval.
10.6.5 You should not use similarity for a new aircraft design with new systems.
10.7 Step 7 – Select Aircraft Verification Method.
10.7.1 LCL A systems should include an aircraft assessment to support compliance with §§ 23.1306(a) (amendment 23-61), 23.2515(a), 25.1316(a), 27.1316(a), or § 29.1316(a).
The aircraft assessment should determine the ATLs where the LCL A systems are installed in the aircraft. You should choose whether you will use either aircraft tests or previous data from similar aircraft types (similarity). For LCL A display systems only, you may select the ETDLs as proposed in Table 4.
10.7.2 If analysis is used to determine the ATLs, you should provide test data to support this analysis. Any analysis results should consider the quality and accuracy of the analysis.
Comprehensive testing, including aircraft level testing, may be required to support the analysis.
10.8 Step 8 – Determine ATLs Using Aircraft Tests.
See SAE ARP5415, User’s Manual for Certification of Aircraft Electrical/Electronic Systems for the Indirect Effects of Lightning, and SAE ARP5416 for guidance on how to determine the ATLs.
10.9 Step 9 – Determine ATLs Using Analysis.
See SAE ARP5415 for guidance on how to analyze aircraft to determine the ATLs.
Acceptance of the analysis method you choose depends on the accuracy of the method. You should confirm your analysis method accuracy using experimental 26
AC 20-136C d ata and d iscuss your planned analysis approach with the cognizant certification branch.
10.10 Step 10 – Determine ATLs Using Similarity.
10.10.1 You cannot use similarity as verification for a new aircraft design with new systems.
10.10.2 You may use similarity to determine the ATLs when there are:
• Only minor differences between the previously certified aircraft and system installation, and the aircraft and system installation to be certified; and
• There is no unresolved in-service history of problems related to lightning strikes to the previously certified aircraft.
10.10.3 If significant differences are found that will affect the aircraft ATLs, you should perform more tests and analyses to resolve the open issues.
10.10.4 To use similarity, you should assess the aircraft, wiring, and system installation differences that can adversely affect the system susceptibility. When assessing a new installation, consider differences affecting the internal lightning environment of the aircraft and its effects on the system. The assessment should cover:
• Aircraft type, equipment locations, airframe construction, structural materials, and apertures that could affect attenuation of the external lightning environment;
• System wiring size, length, and routing; wire types (whether parallel or twisted wires), connectors, wire shields, and shield terminations;
• Lightning protection devices such as transient suppressors and lightning arrestors;
and
• Grounding and bonding.
10.11 Step 11 – Determine Transient Levels Using RTCA/DO-160 Section 22 Guidance for LCL A Displays Only.
10.11.1 You may select ETDLs for your LCL A display system using guidance in this section, without specific aircraft test or analysis. LCL A displays involve functions for which the pilot will be in the loop through pilot/system information exchange. LCL A display systems typically include the displays; symbol generators; data concentrators; sensors (such as attitude, air data, and heading sensors); interconnecting wiring; and associated control panels.
10.11.2 This approach should not be used for other LCL 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 LCL A systems require a more rigorous lightning transient compliance verification program.
AC 20-136C
10.11.3 Y ou should use the information in Table 4 to evaluate your aircraft and system installation features to select appropriate ETDLs for your system. Table 4 defines test levels for ETDLs, based on RTCA/DO-160 section 22, Tables 22-2 and 22-3. Provide the cognizant certification branch with a description of your aircraft and display system installation features and compare these to the information in Table 4 to substantiate the ETDL selected for your aircraft and LCL A display system installation. When selecting ETDLs using guidance provided in Table 4, an acceptable margin between anticipated ATLs for display system installations is incorporated in the selected ETDLs.
AC 20-136C Ta ble 4. Equipment Transient Design Level - LCL A Di splays RTCA/ DO-160, SECTION 22 LEVEL
DISPLAY SYSTEM INSTALLATION LOCATION Level 5 Use this level when the equipment under consideration, its associated wire bundles, or other components connected by wiring to the equipment, are in aircraft areas exposed to very severe lightning transients. These areas are:
• Areas with composite materials whose shielding is not very effective;
• Areas where there is no guarantee of structural bonding; and
• Other open areas where there is little shielding.
You can also use this level to cover a broad range of installations.
You may need higher ETDLs when there are high current density regions on mixed conductivity structures (such as wing tips, engine nacelle fin, and so on) because the system wiring may divert some of the lightning current. If you are the system designer, apply measures to reduce the need for higher ETDLs.
Level 4 Use this level when the equipment under consideration, its associated wire bundles, or other components connected by wiring to the equipment, are in aircraft areas exposed to severe lightning transients. We define these areas as outside the fuselage (such as wings, fairings, wheel wells, pylons, control surfaces, and so on).
Level 3 Use this level when the equipment under consideration, its associated wire bundles, and other components connected by wiring to the equipment, are entirely in aircraft areas with moderate lightning transients. We define these areas as the inside metal aircraft structure or composite aircraft structure whose shielding is as effective as metal aircraft structure, without measures to reduce lightning coupling to wires. Examples of such areas are avionics bays not enclosed by bulkheads, cockpit areas, and locations with large apertures (that is, doors without electromagnetic interference (EMI) gaskets, windows, access panels, and so on).
Current-carrying conductors in these areas (such as hydraulic tubing, control cables, wire bundles, metal wire trays, and so on) are not necessarily electrically grounded at bulkheads. When few wires exit the areas, either use a higher level (that is, Level 4 or 5) for these wires or offer more protection for these wires.
Level 2 Use this level when the equipment under consideration, its associated wire bundles, and other components connected by wiring to the equipment, are entirely in partially protected areas. We define these areas as the inside of a metallic or composite aircraft structure whose shielding is as effective as metal aircraft structure, if you take measures to reduce the lightning coupling to wires.
Wire bundles in these areas pass through bulkheads and have shields that end at the bulkhead connector. When a few wires exit these areas, use either a higher level (that is, Level 3 or 4) or provide more protection for these wires. Install wire bundles close to the ground plane, to take advantage of other inherent shielding from metallic structures. Current-carrying conductors (such as hydraulic tubing, control cables, metal wire trays, and so on) are electrically grounded at all bulkheads.
Level 1 Use this level when the equipment under consideration, its associated wire bundles, and other components connected by wiring to the equipment are entirely in well-protected aircraft areas. We define these areas as electromagnetically enclosed.
AC 20-136C
10.12 Step 12 – Verify Compliance with the Requirements.
You should compare the verified system ETDLs with the aircraft ATLs and determine if an acceptable margin exists between the ETDLs and ATLs. Margins account for uncertainty in the verification method. As confidence in the verification method increases, the margin can decrease. An ETDL exceeding the ATL by a factor of two is an acceptable margin for LCL A systems if this margin is verified by aircraft test or by analysis supported by aircraft tests. For LCL A display systems where the ETDLs are determined using guidance provided in Table 4, an acceptable margin is already incorporated in the selected ETDLs. For other verification methods, the margin should be agreed upon with the cognizant certification branch.
10.13 Step 13 – Take Corrective Measures.
10.13.1 When your system fails to meet the certification requirements, corrective actions should be selected. The changes or modifications you make to the aircraft, system installation or the equipment may require more testing and analysis.
10.13.2 To meet the certification requirements, you may need to repeat system qualification testing, or aircraft testing and analysis (in whole or in part). You also may need to modify the system or installation to get certification. You should review these changes or modifications with the cognizant certification branch to determine if they are significant. If these changes or modifications are significant, update your lightning certification plan accordingly. The updated certification plan should be resubmitted to the certification branch for review.
10.14 Compliance for LCL A Systems on Level 1, 2, 3, and 4 Airplanes Certified Under Part 23.
10.14.1 Airplane certification levels 1, 2, 3, and 4 are defined in § 23.2005 (established by amendment 23-64). Airplane certification classes I, II, III, and IV are defined in AC
23.1309-1.
10.14.2 The following test levels may be used for LCL A integrated systems on normal category level 1, 2, 3, and 4 airplanes (certification class I, II, III, and IV). Equipment testing may be acceptable if you show that equipment in the LCL A systems can be operated and tested independently, as well as can be effectively monitored to verify no adverse effects to the system and function. Otherwise, you should perform integrated system lightning tests as discussed in step 5 (refer to paragraph 10.5). The system should comprise all equipment and wiring needed to perform the function. One or more of these systems with redundant channels may perform the same function. When there are multiple systems with redundant channels performing the same function, it is only necessary for one of the multiple systems’ redundant channels to meet the requirements in § 23.1306(a) (amendment 23-61) or § 23.2515(a).
10.14.3 Level 1 airplanes certificated under part 23 meet the same requirements for lightning compliance as shown in paragraph 10.14.5 below. Level 2 and 3 airplanes certificated under part 23 meet the requirements for lightning as shown in paragraph 10.14.6 below.
AC 20-136C Lev el 4 airplanes certified under part 23 meet the requirements for lightning as shown in par agraph 10.5.
10.14.4 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 part 23 airplanes, including any required changes for acceptance, are available at the FAA Small Airplanes Design Approvals website (reference “Industry Standards”).
10.14.5 For level 1 airplane LCL A systems, you may perform lightning induced transient tests using RTCA/DO-160, section 22. Test categories include pin injection and cable bundle evaluations with single stroke, multiple stroke, and multiple burst waveform sets:
• Primary aluminum structure - refer to RTCA/DO-160G, category A2J2L2 or RTCA/DO-160D, change 3, E, F, category B2K22.
• Primary carbon fiber or fiberglass structure - refer to RTCA/DO-160G, category B2K2L2 or RTCA/DO-160D, change 3, E, F, category B2K22.
10.14.6 For level 2 and 3 airplane LCL A systems, you may perform lightning induced transient tests using RTCA/DO-160, section 22. Test categories include pin injection and cable bundle evaluations with single stroke, multiple stroke, and multiple burst waveform sets:
• Primary aluminum structure - refer to RTCA/DO-160G, category A3J3L3 or RTCA/DO-160D, change 3, E, F, category A3J33.
• Primary carbon fiber or fiberglass structure - refer to RTCA/DO-160G, category B3K3L3 or RTCA/DO-160D, change 3, E, F, category B3K33.
10.14.7 The electronic engine control and ignition systems on part 23 airplanes must be classified as LCL A [lightning effects that result in loss of thrust (or power) control should be considered catastrophic]. You may design, test, and install the engine control system using the guidance provided in AC 33.28-3. Develop and install appropriate electrical bonding features for the engine control system using the guidance in AC
33.28-3.
10.14.8 The electronic propeller control system on part 23 airplanes must be classified as LCL A [lightning effects that result in loss of power control should be considered catastrophic]. You may design, test, and install the propeller system using the guidance provided in AC 35.23-1. Develop and install appropriate electrical bonding features for the propeller control system using the guidance in AC 35.23-1.
10.14.9 The airframe should incorporate low impedance electrical conductors for lightning current to flow through the airplane. The low impedance conductors should be incorporated into the basic structure of the airplane.
• For airplanes with primarily aluminum structure, the aluminum skin provides a low impedance electrical conductor. Standard rivets and bolts provide adequate 31
AC 20-136C ele ctrical bonding between permanent structural joints. Electrical bonding straps or jumpe rs should be installed on moving parts or for removable panels or parts.
• For airplanes with primarily carbon fiber or fiberglass structure, you should incorporate metal mesh, metal foil, or expanded metal foil onto the external surfaces of the airplane composite structure. This mesh or foil should be joined together electrically and provide a continuous electrical conductor between the extremities of the airplane. Use of metallic components internal to the structure of the airplane may also be used to provide similar shielding for equipment and its wiring.
• For airplanes constructed of tube and fabric, the tube skeleton may be considered as the low impedance electrical path through the airplane. Electrical bonding may also be achieved using bonding straps or jumpers where required to electrically bond other metallic sub-structure that might be relied upon to provide bonding for equipment.
10.14.10 Electrical bonding specifications and verifications should be developed and implemented on the production drawings and instructions for continued airworthiness.
11 STEPS TO LCL B AND C SYSTEM LIGHTNING COMPLIANCE.
Steps 1 through 8 listed below in this section may be used to demonstrate compliance for LCL B and C systems with §§ 23.1306(b) (amendment 23-61), 23.2515(b),
25.1316(b), 27.1316(b), or § 29.1316(b). Section 23.2515(b) only applies to LCL B systems with hazardous failure conditions (reference Table 2).
11.1 Step 1 – Identify LCL B and C Systems.
11.1.1 Identify your LCL B and C systems as described in paragraphs 7.2 and 7.3.
11.1.2 Define the detailed system performance pass/fail criteria. You should get certification branch concurrence on this criterion before you start testing or analyzing your LCL B and C systems.
11.1.3 Figure 3 illustrates a process you can use to demonstrate that your LCL B and C systems comply with 14 CFR requirements.
AC 20-136C Figure 3. Typical Compliance Process for LCL B and C Systems Identify LOL B and C Systems
(7) Define System ugnitning Protect o Features (2) Define System ETDLS
(3)
(4) Select ET DL Verification Method Verify System Verify System ETDLs by ET DLs by Qualificaton Tests Similanty
(5) (Б) Verification ET DL Modify System Acceptable? Protection
(7) (8)
(n) = Step number as described in paragraph 11 of this AC Lightring Compliance De mon strated 33