14 — EMC: emissions and susceptibility are different evidence
DO-160 Display Qualification | A-P02 — Draft / Not Released
Learning objective: Plan Sections 15 and 19–21 with representative modes, cables and observation.
Image: NASA Glenn Research Center · Test setup in the Electromagnetic Interference Laboratory · NASA imagery; generally not subject to US copyright. Source image retained unchanged; displayed at reduced size.
Understand the direction of the effect
Magnetic effect (Section 15) concerns the equipment's effect on a compass environment and associated separation considerations. Induced signal susceptibility (Section 19) addresses disturbances coupled into interconnecting circuits under its methods. Radio-frequency susceptibility (Section 20) tests response to RF disturbances. RF emissions (Section 21) measures interference generated by the equipment. Their purposes and limits differ.
Display clocks, high-speed links, switch-mode supplies, touch scanners, backlight PWM and heaters can create or respond to interference. The final enclosure, conductive coatings, connectors, shields and bond paths form part of the tested system. A bare electronics board in a temporary metal box is not automatically representative of the finished touch display.
Why no single universal V/m limit appears here
RF susceptibility categories involve frequency ranges, conducted and radiated methods, modulation and levels. Emission limits use specified frequency-dependent curves, bandwidths and detector settings. Selecting one headline field-strength number loses essential conditions. The matrix must identify the complete category and applicable curves/methods, then the procedure supplies the normative detail.
Find sensitive and noisy modes
The thermally worst mode may not produce the largest emissions or worst susceptibility. Review clocking, interface activity, backlight PWM duty, touch scanning and processor load. Conduct development characterization where useful to choose representative qualification modes. Keep mode rationale and actual settings in the report.
Use a dynamic frame counter, controlled input changes and synchronized observation to detect freezes, false colors, missing symbols and unintended control actions. An optical camera or isolated link can reduce monitoring-system interference, but its image quality and timing still need validation. A static logo is a poor freeze detector.
Exercise
A display passes emissions with a short cable and a 360-degree shield termination. The aircraft uses a long unshielded extension. Worked response: the changed cable can alter emissions, susceptibility and induced transient coupling. Compare the installation to the qualification and installation limits; do not transfer the report solely because the display part number is unchanged.
Installed connection
Equipment RF testing supports, but does not alone settle, aircraft HIRF compliance or compatibility with the installed equipment environment. Use the accepted compliance plan and FAA AC 20-158B where applicable to connect the allocated threat, equipment capability and installation evidence.
EMI and EMC for fixed-wing aircraft and helicopters
Both aircraft types require a traceable connection between the display’s function, the installed electromagnetic environment and the equipment evidence. DO-160 does not supply one universal helicopter EMC category or a fixed multiplier over airplane levels. Airframe construction, shielding, bonding, apertures, harness routing, cable terminations and antenna proximity can matter more than the aircraft label.
| Evidence layer | What to establish for either aircraft type | Helicopter comparison to make explicitly |
|---|---|---|
| Display equipment | Select and record the complete applicable Section 15 and Sections 18–21 methods, categories and limits. Monitor display corruption, freezing, resets, dimming and control behavior. | Check the actual power/harness arrangement and mounting bonds; an isolator that helps vibration can change the electrical bonding design. |
| Intersystem compatibility | Demonstrate the required compatibility in the installed equipment environment, in both directions: interference into the display and interference generated by it. | Select relevant installed radio transmit/receive conditions and electrical loads for that aircraft and mission. Neighboring systems are interaction partners, not additional equipment being qualified by this course. |
| HIRF protection | Relate the applicable aircraft HIRF environment and functional criticality to integrated-system test levels and installation evidence. | Use the rotorcraft certification basis and applicable coupling/attenuation method. Do not reuse an airplane transfer function solely because the display part number matches. |
| Lightning and ESD | Allocate Section 22 induced-transient, Section 23 direct-effects and Section 25 ESD evidence separately where applicable. | Assess the actual installation and exposure. An EMC chamber pass or a helicopter vibration pass does not establish these separate protections. |
HIRF has a display-specific comparison worth knowing
FAA AC 20-158B §10.11 provides a generic-transfer-function and attenuation approach for eligible Level A display systems. Appendix A distinguishes airplane transfer functions by fuselage length and provides a separate rotorcraft curve in Figure A-4. Apply the method only within its stated display-system scope and accepted compliance plan; it is not permission to assign the same credit to all electronic systems.
Attenuation credit also depends on where the display and associated wiring are installed. Appendix A.2 distinguishes unshielded areas from areas with minimal, some or moderate shielding, with corresponding installation conditions. Do not assume a generic cockpit attenuation simply from a metal display enclosure or an aircraft name. The aircraft external field, the internal field at the display and the induced current in its harness are different quantities.
For US certification planning, record the applicable certification basis and amendment: Part 23 or 25 for the relevant airplane category, or Part 27 or 29 for the relevant rotorcraft category, including applicable HIRF and lightning provisions. Different functional consequences can change the required protection and recovery behavior. A primary flight display and a nonessential cabin display should not inherit the same assumptions merely because both use an LCD.
Installed EMC exercise
A display with fixed-wing equipment reports is proposed for a helicopter. Its new installation uses vibration isolators, a longer harness, different shield terminations and a radio antenna near the cockpit. Worked response: review the qualification configuration and aircraft exposure, establish the mount-bond arrangement, compare harness coupling and shielding, and resolve affected equipment and installed tests. Demonstrate the required display behavior while the allocated onboard equipment states are exercised. Keep vibration approval, equipment EMC, aircraft HIRF and lightning conclusions distinct.
Sources: RTCA DO-160G, §§15, 18–23 and 25; FAA AC 20-158B, §§10.7–10.12 and Appendix A. Planning examples are engineering applications, not prescribed test levels.
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