Definition
To convert an atom or molecule, which is normally electrically neutral, into a charged particle (an ion) by adding or removing one or more electrons. In aviation, ionization is involved in phenomena such as electrical discharge in spark plugs, the behavior of the upper atmosphere affecting radio propagation, and the operation of certain fire and smoke detectors.
Plain English
To give an atom an electrical charge by adding or stripping away one of its electrons. Once that happens, the atom becomes an ion and behaves differently — it can carry electricity, react chemically, or affect radio signals.
Context Anchor
Seen in ignition, spark plug, high-voltage electrical, and some fire or smoke detection discussions.
Derivation
From the Greek 'ion,' meaning 'going' — chosen by 19th-century scientists because charged particles move toward electrodes when an electric field is applied. The verb 'ionize' simply means 'to make into an ion.' Knowing that an ion is a particle that moves under electrical influence helps explain why ionized air conducts electricity (as in a spark) and why ionized layers in the atmosphere bend radio waves.
Why Pilots Care
Ionization is what makes a spark plug work — the high-voltage current ionizes the air gap so electricity can jump across and ignite the fuel-air mixture. It's also why HF radio communication is possible over long distances: the ionized layers of the upper atmosphere reflect certain radio frequencies back to Earth.
Grounding Statement
When a strong voltage is applied across a small gap, the gas in the gap can become charged enough for electricity to jump through it.
Intuition Check
Ionize does not mean simply heat up, burn, or glow. It means give particles an electric charge so they can carry electricity.
Example Sentence 1
The high voltage from the magneto ionizes the air in the spark plug gap, allowing a spark to jump and ignite the mixture.
Example Sentence 2
Strong electric fields in a thunderstorm ionize the air between cloud and ground, creating a lightning channel.