Electromagnetic Compatibility Testing

The advantages are clear to us of introducing digital electronic technology in aircraft electrical or electronic systems, it has enabled unprecedented expansion of aircraft system functionality and evolution of aircraft function automation. An electromagnetic environment, a form of energy, is created by electrical/electronic equipment which poses a threat to the proper operation of systems that depend on such equipment.

Electrical/electronic systems, subject to EME threat, are run by computers susceptible to upset from lightning and sources that radiate RF.

Momentary and transient they may be, on equipment that is generally less susceptible than some older equipment, upsets to digital circuits may not recover to the proper state and may require external intervention. Avoidance has become an industry, aerospace electromagnatic compatibility testing.

Upset is probably an inadequate word to describe lightning-induced transients which produce hard faults or damage to circuit components.

Any immunity to damage of electronic components can be determined by circuit impedances of interconnecting loops, of wiring, of materials used, integrated circuit leads, PC board trace spacing, etc.

Lightning and High Intensity Radiated Field (HIRF) are the greatest safety issue for aircraft electrical/electronic systems.

Exacerbated by the increasing use of electrical and electronic systems in aircraft safety systems themselves, by the use of composite materials in aircraft construction (decreased conductivity) forcing the lightning channel  into and through the aircraft structure without attenuation. The effects of lightning like dielectric puncture, blasting, melting or fuel ignition have been recognized as flight hazards for decades.

HIRF and Aerospace EMC testing

Installation of electrical equipment, controls, and wiring should preclude the simultaneous damaging of any other electrical unit or system essential to aircraft safe operation in the event of a strike. Cables, too, should be grouped, routed, and spaced to minimize the effect on other cables.

Both lightning and HIRF interactions produce internal fields. Lightning can also produce substantial voltage drops across the aircraft structure. The poorer the conductivity of structural materials, the greater the possibility that there are voltage differences across the structure, magnetic fields.

Electromagnetic events are complex interactions. Points of entry may be seams, cable entries or windows. Considerable expertise is required to manage these issues.