Definition
Unwanted electrical disturbance, radiated or conducted, that disrupts the normal operation of avionics, electrical systems, or communication and navigation equipment on an aircraft. EMI can come from external sources (lightning, radio transmitters, power lines) or from internal sources (motors, generators, switching circuits, poorly shielded wiring).
Plain English
Stray electrical noise from one piece of equipment that messes with another piece of equipment nearby.
Context Anchor
Seen in aircraft maintenance, avionics troubleshooting, radio problems, wiring installation, and equipment shielding discussions.
Derivation
From electro- (electric), magnetic (magnetism), and interference (something that gets in the way). The name describes exactly what it is: electric and magnetic energy from one source getting in the way of another circuit.
Why Pilots Care
EMI can cause loss of communication, inaccurate navigation data, or erratic instrument readings, creating immediate safety and decision-making problems.
Analogy
EMI is like a noisy conversation happening next to someone giving you instructions. The instructions may still be there, but the extra noise makes them hard for the equipment to receive clearly.
Intuition Check
Do not think EMI only means radio static. In aviation, it can be any unwanted electrical or magnetic energy that disrupts aircraft electronic equipment.
Example Sentence 1
After installing the new transponder, the technician rerouted a cable to reduce EMI affecting the VHF radio.
Example Sentence 2
Maintenance replaced the faulty strobe light power supply after confirming it was the source of EMI affecting the ADF receiver.