Final answer:
The function of a capacitor in an aircraft ignition system is to store electric charge.
Step-by-step explanation:
In an aircraft ignition system, one of the functions of the capacitor is to store electric charge. Capacitors have applications ranging from filtering static out of radio reception to energy storage in heart defibrillators. When battery terminals are connected to an initially uncharged capacitor, equal amounts of positive and negative charge, +Q and -Q, are separated into its two plates. The capacitor remains neutral overall, but we refer to it as storing a charge Q in this circumstance.