FAA Powerplant Written Practice Test

What happens when the contact points in a magneto open?

1. Current flows to the battery

2. A spark is generated

3. The voltage is grounded

4. The ignition coil charges

The correct answer is: A spark is generated

When the contact points in a magneto open, it causes a sudden interruption in the current flowing through the primary winding of the ignition coil. As the current is stopped, the magnetic field that has been built up around the coil starts to collapse. This rapid change in magnetic flux induces a high voltage in the secondary winding of the ignition coil due to Faraday's law of electromagnetic induction. This induced high voltage is what generates a spark at the spark plug, igniting the air-fuel mixture in the combustion chamber of the engine. The process ensures that the engine can operate efficiently by producing the necessary spark for combustion. This fundamental operation is critical in the functioning of magneto ignition systems commonly used in aircraft, particularly those with reciprocating engines. When evaluating the other possible answers, they either describe actions that do not occur during the opening of the contact points or pertain to systems not directly involved with the spark generation process in magneto systems.