Table 3. Equipment Transient Design Levels - Level A Displays
RTCA/DO- 160 Section 22 Level Level 5 Display System Installation Location 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.
Use this level when the equipment under consideration, its associated wire bundles, or Level 4 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 Level 3 wings, fairings, wheel wells, pylons, control surfaces, and so on).
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 thes e areas as the inside metal aircraft structure or composite aircraft structure whose shielding without improvements is as effective as metal aircraft structure. Ex amples 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.
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.
Level 2 Wire bundles in these areas pass through bulkheads, and have shields that end at the bulkhead connector. When a few wires exit thes e 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.
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.
Level 1 13
g. Verify System ETDLs Using System Qualification Tests.
(1) You should identify the equipment, components, sensors, power systems, and wiring associated with the Level A system undergoing ETDL verification tests, specifically considering the system functions whose failures have catastrophic failure consequences. For complex Level A systems, the system configuration may include redundant equipment, multiple power sources, multiple sensors and actuators, and complex wire bundles. Define the system configuration used for the ETDL verification tests. You should obtain the cognizant ACO approval of your system configuration for ETDL verification tests.
(2) 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.
Show 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 S ection 22 provides acceptable test procedures and waveform set definitions. In addition, SAE ARP 5416 provides acceptable test methods for complex and integrated systems.
(3) You should evaluate any system effects observed during the qualification tests to ensure they do not adversely affect the system’s continued performance. The Level A system performance should be evaluated for functions of which failures or malfunctions would prevent the continued safe flight and landing of the aircraft. Other functions performed by the system of which failures or malfunctions 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 Section 9. You should obtain the cognizant ACO approval of your evaluation.
h. Verify System ETDLs Using Existing System Data (Similarity).
(1) You may base your ETDL verification on similarity to previously certified systems without performing more tests. You may do this when:
(a) There are only minor differences between the previously certified system and installation, and the system and installation to be certified;
(b) There are no unresolved in-service system problems related to lightning strikes on the previously certified system; and
(c) The previously certified system ETDLs were verified by qualification tests.
(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:
(a) System interface circuits;
(b) Wire size, routing, arrangement (parallel or twisted wires), connector types, wire shields, and shield terminations;
(c) Lightning protection devices such as transient suppressors and lightning arrestors;
(d) Grounding and bonding; and
(e) System software, firmware, and hardware.
(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.
(4) You should assess every system, even if it uses equipment and installation techniques that have previous certification approval.
(5) You should not use similarity for a new aircraft design with new systems.
i. Verify Compliance to 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 Level A systems, if this margin is verified by aircraft test or by analysis supported by aircraft tests. For Level A display systems where the ETDLs are determined using guidance provided in Table 3, an acceptable margin is already incorporated in the selected ETDLs. For other verification methods, the margin should be agreed upon with the cognizant ACO.
j. Take Corrective Measures.
(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.
(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 ACO 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 ACO for review.
9. Level B and C System Lightning Certification.
Yes D
a. Identify Level B and C Systems.
(1) Identify your Level B and C systems as described in paragraph 6.c.
(2) Define the detailed system performance pass/fail criteria. You should get ACO concurrence on this criterion before you start testing or analyzing your Level B and C systems.
(3) Figure 3 illustrates a process you can use to show that your Level B and C systems comply with 14 CFR requirements.
Figure 3. Typical Compliance Process for Level B and C Systems Identify Level B and C Systems
(9.a) Define System ETDLs
(9.b) Select ETDL Verification Method Verify System ETDLs by Qualification Tests
(9.c) Verify System ETDLs by Similarity
(9.d) ETDL Verification Acceptable?
(9.e) Lightning Compliance Demonstrated Modify System Protection
(9.f) Define System Lightning Protection Features Numbers in parenthesis refer to sections in this AC 16
b. Establish ETDLs.
(1) You may use the ATLs determined during aircraft tests or analyses performed for Level A systems to establish appropriate ETDLs for Level B and C systems.
(2) Alternatively, you may use the definitions in RTCA/DO-160, Section 22 to select appropriate ETDLS for your Level B and C systems. The following should be considered when selecting an appropriate level:
(a) Use RTCA/DO-160, Section 22, Level 3 for most Level B systems.
(b) For Level B systems and associated wiring installed in aircraft areas with more severe lightning transients, use RTCA/DO-160, Section 22, Level 4 or 5 as appropriate to the environment. Examples of aircraft areas with more severe lightning transients are those external to the fuselage, areas with composite structures showing poor shielding effectiveness, and other open areas.
(c) Use RTCA/DO-160, Section 22, Level 2 for most Level C systems.
(d) For Level C systems installed in aircraft areas with more severe lightning transients, use RTCA/DO-160, Section 22, Level 3. Ex amples of aircraft areas with more severe lightning transients are those external to the fuselage, areas with composite structures showing poor shielding effectiveness, and other open areas.
(e) Provide the cognizant ACO with a description of your aircraft and system installation features to substantiate the RTCA/DO-160, Section 22 levels selected for your system.
c. Verify System ETDLs Using Equipment Qualification Tests.
(1) You should perform equipment qualification tests using the selected test levels and single stroke, multiple stroke, and multiple burst waveform sets. Show that the equipment operates within the defined pass/fail criteria during these tests. No equipment damage should occur during these equipment qualification 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.
(2) You should evaluate any equipment effects observed during the qualification tests to ensure these do not adversely affect the system’s continued performance. You should obtain the cognizant ACO approval of your evaluation.
(3) Multiple stroke and multiple burst testing is not required if an analysis shows that the equipment is not susceptible to upset or, that the equipment may be susceptible to upset, but a reset capability exists so the system recovers in a timely manner.
d. Verify System ETDLs Using Existing Equipment Data (Similarity).
(1) You may verify ETDLs by similarity to previously certified systems without performing more tests. You may do this when:
(a) There are only minor differences between the previously certified system and installation, and the system and installation to be certified;
(b) There are no unresolved in-service system problems related to lightning strikes on the previously certified system; and
(c) The previously certified system ETDLs were verified by qualification tests.
(2) The assessment should cover:
(a) Equipment interface circuits;
(b) Wire size, routing, arrangement (parallel or twisted wires), connector types, wire shields, and shield terminations;
(c) Lightning protection devices such as transient suppressors and lightning arrestors;
(d) Grounding and bonding; and
(e) Equipment software, firmware, and hardware.
(3) If significant differences are found that will affect the systems and installations, you should perform more tests and analyses to resolve the open issues.
e. Verify Compliance to the Requirements. You should show that the Level B and C systems meet their defined acceptance criteria during the qualification tests at the selected system ETDLs.
f. Take Corrective Measures. When your system fails to meet the certification requirements, you should decide on corrective actions. If you change or modify the system or installation, you may need to repeat equipment qualification testing. You should review these changes or modifications with the cognizant ACO 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 ACO for review.
10. Maintenance and Surveillance.
a. You should identify the minimum maintenance required for the aircraft electrical and electronic system lightning protection in the instructions for continued airworthiness (ICA). You should define the requirements for periodic and conditional maintenance and surveillance of lightning protection devices or features to ensure acceptable protection performance while the 18
aircraft is in service. Avoid using devices or features that may degrade with time because of corrosion, fretting, flexing cycles, or other causes. Alternatively, identify when to inspect or replace these devices.
b. You should define the inspection techniques and intervals needed to ensure that the aircraft and system lightning protection remains effective in service. Also, identify built-in test equipment, resistance measurements, continuity checks of the entire system, or other means to determine your system’s integrity periodically and conditionally.
c. See SAE ARP 5415 for more information on aircraft lightning protection maintenance and surveillance.
Susan J. M. Cabler Assistant Manager, Aircraft Engineering Division 19
Appendix 1 Appendix 1. Related Documents and How to Get Them
1. Title 14 of the Code of Federal Regulations (14 CFR). You can get copies of the following 14 CFR sections from the Superintendent of Documents, Government Printing Office, Washington, D.C. 20402-9325. Telephone 202-512-1800, fax 202-512-2250. You can also access copies from the Government Printing Office (GPO), electronic CFR Internet website at www.access.gpo.gov/ecfr/.
a. Part 23, Airworthiness Standards: Normal, Utility, Acrobatic, and Commuter 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 § 23.1309 Equipment, systems, and installations § 23.1306 Electrical and electronic system lightning protection § 23.1529 Instructions for continued airworthiness
b. 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
c. Part 27, Airworthiness Standards: Normal Category Rotorcraft :
§ 27.610 Lightning and static electricity protection § 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
d. Part 29, Airworthiness Standards: Transport Category Rotorcraft:
§ 29.610 Lightning and static electricity protection § 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 A1-1
Appendix 1
e. 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 )
2. Federal Aviation Administration (FAA) Advisory Circulars (AC). You can access copies of the following ACs at www.faa.gov/regulations_policies/advisory_circulars/.
Note: The ACs referenced in this document refer to the current revisions.
a. AC 20-155, SAE Documents to Support Aircraft Lightning Protection Certification.
b. AC 21-16, RTCA Document DO-160 Versions D, E, F, and G, Environmental Conditions and Test Procedures for Airborne Equipment.
c. AC 23-17, Systems and Equipment Guide for Certification of Part 23 Airplanes and Airships.
d. AC 23.1309-1, System Safety Analysis and Assessment for Part 23 Airplanes.
e. AC 25.1309-1, System Design and Analysis.
f. AC 27-1, Certification of Normal Category Rotorcraft.
g. AC 29-2, Certification of Transport Category Rotorcraft.
3. Industry Documents.
Note: The industry documents referenced in this section refer to the current revisions or regulatory authorities accepted revisions.
a. European Organization for Civil Aviation Equipment (EUROCAE). You can get copies of the following documents from EUROCAE, 17 rue Hamelin, 75116 Paris, France.
Telephone 33 (0) 1 4505 7188, fax 33 (0) 1 4505 7230, website www.eurocae.net.
(1) EUROCAE ED-14, Environmental Conditions and Test Procedures for Airborne Equipment.
(2) EUROCAE ED-105, Aircraft Lightning Test Methods.
(3) EUROCAE ED-113, Aircraft Direct Effects Certification.
b. RTCA. You can get copies of RTCA/DO-160, Environmental Conditions and Test Procedures for Airborne Equipment, from RTCA, Inc., 1150 18th Street NW, Suite 910, Washington, D.C. 20036. Telephone 202-833-9339, fax 202-833-9434, website www.rtca.org.
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Appendix 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: Use of RTCA/DO-160D, Change Notice 3, or later revisions are acceptable.
c. SAE International. You can get copies of the following documents from SAE Customer Service, 400 Commonwealth Drive, Warrendale, PA 15096-0001. Telephone 724-776-4970, fax 724-776-0790, website www.sae.org.
(1) Aerospace Recommended Practice (ARP) 4754, Guidelines for Development of Civil Aircraft and Systems.
(2) ARP 4761, Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment.
(3) ARP 5412, Aircraft Lightning Environment and Related Test Waveforms.
(4) ARP 5414, Aircraft Lightning Zoning.
(5) ARP 5415, User’s Manual for Certification of Aircraft Electrical/Electronic Systems Against the Indirect Effects of Lightning.
(6) ARP 5416, Aircraft Lightning Test Methods. This document is technically equivalent to EUROCAE ED-105. Anywhere th ere is a reference to ARP 5416, EUROCAE ED- 105 may be used.
(7) ARP 5577, Aircraft Lightning Direct Effects Certification.
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