NEWTON, N.H. — Aircraft electronics can interfere with one another even when each system works as designed. Radio transmissions, electrical wiring and onboard equipment can generate electromagnetic energy that reaches nearby avionics, sometimes disrupting signals or affecting equipment performance.

Engineers call this electromagnetic interference (EMI), and they must account for it when designing, installing and testing avionics.

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What causes electromagnetic interference?

Some electronic devices produce radio-frequency signals intentionally, while others create electrical noise as a byproduct of switching circuits, motors or power supplies.

For example, a transmitter operating near sensitive avionics equipment may introduce unwanted signals into a receiver. Electrical noise from a power converter can also travel through wiring and reach other components. Engineers generally distinguish between conducted and radiated interference.

Conducted interference travels along physical connections, including power cables and signal wiring. Radiated interference travels through electromagnetic fields and can impact equipment without a direct electrical connection.

Both forms can create problems when systems lack sufficient protection or operate too close to sensitive equipment.

How does EMI affect aircraft avionics?

The effects depend on the equipment involved, the strength of the interference and the frequencies at which it occurs. In communications systems, interference can lessen signal quality, making transmissions difficult to receive. Navigation receivers may struggle to detect weak satellite signals when stronger unwanted emissions reach their antennas.

Other avionics can experience inaccurate measurements or temporary malfunctions if interference reaches vulnerable circuits. These problems do not always involve complete equipment failure. A system may continue operating while producing unreliable information or experiencing intermittent errors.

Aircraft designers therefore must evaluate how electronic systems interact rather than considering each component independently.

How do engineers prevent electromagnetic interference?

Engineers use several design techniques to reduce unwanted emissions and protect sensitive equipment. Shielding is one form of protection. Conductive enclosures and cable shields can limit the electromagnetic energy entering or leaving a device. Their effectiveness depends on the materials and connections in the shielding.

Filtering is another approach. Engineers install filters in power and signal circuits to minimize unwanted electrical noise while allowing intended signals to pass. Cable routing also matters. Separating sensitive signal wiring from high-power cables can reduce interference, especially when engineers account for cable length, grounding and installation geometry.

Grounding and bonding help establish controlled electrical connections between equipment and aircraft structures. Poor connections can create unintended paths for electrical noise or reduce the effectiveness of shielding.

No single technique addresses every interference problem. Engineers often combine these measures based on the aircraft's electrical architecture and operating environment.

How do engineers test avionics for EMI?

Electromagnetic compatibility (EMC) testing helps engineers determine whether equipment can operate in its intended environment without causing unacceptable interference or experiencing disruption from nearby systems.

Testing generally examines two areas: emissions and susceptibility. Emissions testing measures the electromagnetic energy equipment produces. Engineers use instruments such as spectrum analyzers, antennas and specialized receivers to locate unwanted signals across specified frequency ranges.

Susceptibility testing evaluates how equipment responds when engineers expose it to electromagnetic disturbances. Depending on the test, they may inject signals into cables or apply electromagnetic fields around the equipment.

Aviation programs commonly use standards such as RTCA DO-160 to establish environmental test procedures, including those involving radio-frequency emissions and susceptibility. The applicable requirements depend on the equipment, aircraft and certification or qualification program.

Engineers also conduct aircraft-level assessments because individual components that pass laboratory tests can still interact unexpectedly after installation.

Why is electromagnetic compatibility important?

Electromagnetic compatibility gives designers a way to address those interactions before they affect aircraft operations. By controlling emissions, protecting sensitive circuits and verifying installed equipment, engineers can reduce the risk of interference as avionics systems become more complex.