Definition
The output coil of a transformer or magneto coil, in which a voltage is induced by the changing magnetic field produced by the primary winding. In an aircraft magneto, the secondary winding consists of many thousands of turns of fine wire wrapped around the same iron core as the primary, and it produces the high voltage (typically around 20,000 volts) that fires the spark plug.
Plain English
It is the second coil of wire in a magneto or transformer. The first coil builds up a magnetic field, and when that field collapses, it pushes a much higher voltage out of this second coil. That high voltage is what jumps the gap at the spark plug.
Context Anchor
Seen in aircraft ignition system and magneto maintenance descriptions.
Derivation
Secondary comes from the Latin secundarius, meaning second in order. Winding refers to wire wound in coils around a core. So secondary winding simply means the second coil in the sequence — the one that receives induced voltage rather than the one that creates the original magnetic field.
Why Pilots Care
A faulty secondary winding produces weak or absent sparks, causing hard starting, misfires, or engine roughness.
Analogy
Think of it like the high-pressure side of a hand pump: the first action starts the motion, and the secondary winding is where the strong output is produced.
Intuition Check
“Secondary” does not mean less important here. It means the second winding in the ignition coil, where the high voltage for the spark plugs is produced.
Example Sentence 1
When the technician traced the misfire to the right magneto, he found an open secondary winding and replaced the coil assembly.
Example Sentence 2
A break in the secondary winding stopped the magneto from delivering a usable spark to the plugs.