DO-160 Section 22 is one of the environmental qualification tests defined in RTCA DO-160.
What DO-160 Section 22 Covers, and Why It Exists
Section 22 addresses a different lightning concern than a direct strike: the transients induced into equipment and wiring when lightning strikes the airframe elsewhere. The category system is genuinely complex, using a multi-character code with waveform-set designators and test-level designators that together define which transient waveforms and severity levels apply. Test procedures split into pin-injection tests, applying transients directly to equipment connector pins, and cable-bundle tests, including both induction and ground-injection methods, reflecting the different paths a lightning-induced transient can take to reach sensitive circuitry.
The Typical Failure Pattern
The shift to composite airframes raised the real-world stakes here directly. Composite skins have higher electrical impedance than the aluminum they replaced, which allows greater voltage and current to couple onto internal wiring during a strike than older metal airframes permitted. The FAA’s AC 20-136B addresses exactly this with its Equipment Transient Design Level and Actual Transient Level framework, a formal recognition that under-qualified equipment on a modern composite airframe can be damaged or upset by induced transients in ways it might not have been on an older aluminum design.
Why Internal Galley Equipment Isn’t Automatically Exempt
It’s tempting to assume equipment mounted inside the pressurized cabin is insulated from lightning. That’s true for direct effects (Section 23), but Section 22 is about induced transients traveling through aircraft wiring, and galley equipment wiring runs through the same airframe as everything else. The relevant question isn’t whether the equipment could be struck directly, it’s whether a strike elsewhere could induce a damaging transient on the wiring it’s connected to, and on a composite airframe that question deserves more scrutiny, not less.
How to Mitigate This
- Don’t assume internal mounting reduces your applicable category, wiring path matters more than mounting location for induced transients
- Treat the multi-character category code as several separate decisions, waveform set and test level aren’t the same thing
- For composite-airframe aircraft, scrutinize the transient design level rather than carrying forward assumptions from aluminum-airframe programs
Further reading: NTSB accident report archive.
How Eminent Helps: Internal mounting doesn’t exempt galley equipment from induced lightning transients, and composite airframes raise the bar. Getting the transient design level right, rather than assuming exemption, is the kind of call we help teams make. See how we support galley insert programs.
