RTCA DO-160 – Section 23.0 – Lightning Direct Effects
The tests described in this section are intended to determine the ability of externally mounted equipment to withstand the direct effects of a lightning strike.
The term “externally mounted equipment” refers to all equipment mounted externally to the main skin of the aircraft and includes all such equipment that is covered only by a dielectric skin or fairing that is an integral part of the equipment.
It also includes connecting cables and associated terminal equipment furnished by the equipment manufacturer as a part of the equipment.
The tests described herein specifically exclude the effects on the tested equipment of voltages and currents induced into the externally mounted equipment and its associated circuitry by means of magnetic or electric field coupling.
Examples of equipment covered by this section are antennae, exterior lights, air data probes, external sensors, and anti-ice and de-ice equipment which are mounted external to the structure (i.e. electrically heated anti-ice boots), magnetic fluid level indicators, fuel filler caps and drain valves.
Examples of equipment typically not covered by this section are equipment that are an integral part of the aircraft structure (i.e., heated or unheated windshields, electrically de-iced leading edges where the de-ice system is an integral part of the leading edge structure or is enclosed by the leading edge structure), and externally mounted equipment that is protected by aircraft nose radomes or dielectric coverings which are specific to the aircraft structure and are not integral with the equipment itself.
Components such as these typically are to be addressed and/or tested as a part of the air-frame lightning certification program specified by the aircraft manufacturer, or by other test method(s) appropriate to the component being qualified.
Two types of direct effects tests are contained in the section: High voltage strike attachment tests and high current physical damage tests. The high voltage strike attachment test is used to determine likely lightning attachment locations on the test object. The high current physical damage test is used to determine the damage that may occur to the test object during a lightning channel attachment to or near the test object.
The high current physical damage test can be used to assess:
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Arc root damage
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Hot spot formation
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Melt-through behavior
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Adequacy of protection
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Behavior of joints (sparking and damage)
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Level of voltage and current induced on electrical conductors interfacing with test object
Typically, high voltage strike attachment tests are performed first to determine the likely lightning attachment locations on the test object. The high current physical damage test is then applied to an attachment location identified during the high voltage testing. Test objects that do not have a dielectric covering may not require high strike voltage attachment tests prior to the high current testing if the likely lightning attachment points can be identified. In such cases the test plan shall define the location on the test object where the high current is to be applied.
Normally the equipment will not be powered up or operating during the tests described herein. In situations where a power-on condition could change the susceptibility of the equipment to the direct effects of lightning, the equipment should be powered up or, alternatively, a means employed to simulate the powered up condition. The need for power or a simulated power condition shall be defined in the test plan.
In some situations it is necessary to evaluate the potential interactions of the test object with other aircraft systems during a lightning attachment.
Two types of interactions commonly evaluated are:
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The characteristics of voltages that are directly injected into the test object wiring and passed along to other aircraft electrical/electronic systems, and
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The potential for arcs/sparks from a test object located in a fuel vapor area.
This section provides procedures for detecting arcing and sparking which may ignite a 200 micro-joule sensitive fuel mixture and measuring directly injected voltages onto the test object wiring. The need for these procedures shall be defined in the test plan.
The following are descriptions of each of the standardized Test Categories:
Category 1A
Intended for equipment externally mounted in those areas of the aircraft identified as Lightning Zone 1A. Zone 1A is all areas of the aircraft surface where a first return stroke is likely during lightning channel attachment with a low expectation of flash hang on.
Category 1B
Intended for equipment externally mounted in those areas of the aircraft identified as Lightning Zone 1B. Zone 1B is all areas of the aircraft surface where a first return stroke is likely during lightning channel attachment with a high expectation of flash hang on.
Category 1C
Intended for equipment externally mounted in those areas of the aircraft identified as Lightning Zone 1C. Zone 1C is all areas of the aircraft surface where a first return stroke of reduced amplitude is likely during lightning channel attachment with a low expectation of flash hang on.
Category 2A
Intended for equipment externally mounted in those areas of the aircraft identified as Lightning Zone 2A. Zone 2A is all areas of the aircraft surface where subsequent return stroke is likely to be swept with a low expectation of flash hang on.
Category 2B
Intended for equipment externally mounted in those areas of the aircraft identified as Lightning Zone 2B. Zone 2B is all areas of the aircraft surface into which a lightning channel carrying a subsequent return stroke is likely to be swept with a high expectation of flash hang on.
Category 3N
Intended for equipment externally mounted in those areas of the aircraft designated as Lightning Zone 3 which have new or novel design features that could significantly reduce the level of protection provided by traditional designs, or which have no proven service history.