Definition
An auxiliary induction coil used to produce a series of high-voltage sparks at one spark plug in each cylinder of a reciprocating engine during starting. The booster coil supplies ignition energy while the engine is turning too slowly for the magnetos to generate a strong enough spark on their own.
Plain English
A small electrical device that creates the strong sparks needed to light the fuel inside the engine while it is being started. Once the engine is running fast enough, the regular ignition system takes over and the booster coil is no longer needed.
Context Anchor
Seen in aircraft engine starting and ignition system descriptions, especially on engines that need extra spark energy during start.
Derivation
Booster comes from boost, meaning to lift or assist. Coil refers to the wound wire inside the device that produces high voltage through electromagnetic induction. Together: a coil that gives the ignition system an assist when it cannot do the job alone.
Why Pilots Care
It ensures dependable engine starts, reducing the risk of hot or flooded starts and improving safety during ground operations.
Intuition Check
Do not read booster coil as something that boosts engine power in flight. It boosts the starting spark, and its job is normally limited to engine start.
Example Sentence 1
The booster coil fires a stream of sparks at the spark plugs while the starter cranks the engine, helping it light off on the first few compression strokes.
Example Sentence 2
During the preflight, the mechanic checked the booster coil for proper operation in the ignition system.