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Can you enlighten me about the airworthiness requirements in the field of lightning, for commercial aviation:

  • Which voltage or intensity is the aircraft required to sustain?
  • How is it demonstrated in practical?

Any major certification agency will be good.

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  • $\begingroup$ Which country are you interested in? $\endgroup$ – acpilot Jul 18 '17 at 0:14
  • $\begingroup$ @acpilot: EASA or FAA. $\endgroup$ – mins Jul 18 '17 at 5:50
  • $\begingroup$ Are you looking for certification of the airframe, or airborne equipment? $\endgroup$ – DeltaLima Jul 18 '17 at 8:11
  • $\begingroup$ @DeltaLima: Primary for airframe, e.g. does one test with some intensity between wingtip and nose, or does one submit the airframe to an electric field using plates, does one check if elevator hinges melt, etc. $\endgroup$ – mins Jul 18 '17 at 18:02
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When dealing with lightning protection, there are two significant areas that must be addressed: direct effects of lightning and indirect effects.

The FAA provides guidance on these two areas in the following advisory circulars:

20-155A - Industry Documents To Support Aircraft Lightning Protection Certification

20-136B - Aircraft Electrical and Electronic System Lightning Protection

The lightning zone analysis from the AC 20-155A will define the test requirements for the airframe and help determine the level of testing for installed equipment based on its location in the aircraft.

At the aircraft level it can be a very complex and drawn out process negotiating the specific testing required with the FAA. Once that is done, requirements and verification for the equipment can be developed. A short summary of that process from AC 20-136B is:

6. Steps for Showing Compliance.
a. The following seven steps describe how you may comply with 14 CFR
23.1306, 25.1316, 27.1316, and 29.1316 requirements for your aircraft’s electrical and electronic systems:
(1) Identify the systems to be assessed.
(2) Determine the lightning strike zones for the aircraft.
(3) Establish the aircraft lightning environment for each zone.
(4) Determine the lightning transient environment associated with the systems.
(5) Establish equipment transient design levels (ETDLs) and aircraft actual transient
levels (ATLs).
(6) Verify compliance to the requirements.
(7) Take corrective measures, if needed.
b. 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 SAE ARP 5577.

Testing of individual LRUs is typically under RTCA document DO-160G - Environmental Conditions and Test Procedures for Airborne Equipment. Section 22 covers Lightning Induced Transient Susceptibility and Section 23 covers Lightning Direct Effects.

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