Definition
A component of a high-tension ignition system consisting of a primary winding, a secondary winding, and an iron core, packaged as a single unit. When current flowing through the primary winding is interrupted, the collapsing magnetic field induces a high-voltage pulse in the secondary winding, which is then delivered to the spark plugs to ignite the fuel-air mixture in the engine cylinders.
Plain English
A sealed unit that turns the low voltage from the aircraft's electrical system into the very high voltage needed to make a spark at the spark plug.
Context Anchor
Seen in aircraft engine ignition-system descriptions, magneto inspections, and troubleshooting for weak or missing spark.
Derivation
From 'coil,' referring to the wire wound in tight loops around an iron core. The looping shape is what allows the device to multiply voltage through electromagnetic induction.
Why Pilots Care
A failed coil assembly produces weak or absent sparks that can cause engine misfiring, power loss, or complete shutdown in flight.
Analogy
It is like a compact electrical step-up unit: a small electrical push goes in, and a much stronger spark-making voltage comes out.
Intuition Check
Do not think of coil assembly as just a coiled piece of wire. In this context, it means the complete ignition part that includes the wound wire and the parts needed to make it work as a high-voltage spark source.
Example Sentence 1
During troubleshooting of a rough-running magneto, the mechanic suspected a failing coil assembly and tested it for proper resistance.
Example Sentence 2
A cracked coil assembly caused intermittent roughness that cleared only after the magneto was removed and rebuilt.