Definition
The portion of magnetic flux produced by an electromagnet, transformer, or motor that does not follow the intended magnetic path through the core or working air gap, and therefore does not contribute to the useful work of the device.
Plain English
Magnetic field lines that 'escape' from the part of the device meant to carry them, and so are wasted instead of doing the job they were meant to do.
Context Anchor
Seen in aircraft electrical system theory, especially when studying coils, transformers, generators, alternators, and electric motors.
Derivation
Leakage means something escaping where it shouldn't, like a leaking pipe. Flux comes from the Latin fluxus, meaning a flow. Together the term describes magnetic 'flow' that has leaked away from its intended path.
Why Pilots Care
Reduces the voltage available for the spark plugs, potentially causing hard starting or rough running if excessive.
Analogy
Think of a flashlight aimed through a doorway. The light that goes through the doorway is useful; the light spilling onto the wall beside it is like leakage flux.
Grounding Statement
In a coil or transformer, not all of the magnetism stays in the path where it can help make useful electrical output.
Intuition Check
Leakage flux is not fluid leaking and it is not electricity spilling out of a wire. It means part of the magnetic field is taking a path where it cannot do useful work.
Example Sentence 1
Excessive leakage flux in the transformer caused a noticeable drop in output voltage.
Example Sentence 2
Excessive leakage flux in the ignition system can lead to weak sparks and engine misfires at high altitudes.