FAA Powerplant Written Practice Test

What is the typical engine response when the ignition switch is moved from both to either left or right?

1. Increase in RPM

2. Significant loss of power

3. Slight drop in RPM

4. No change in RPM

The correct answer is: Slight drop in RPM

When the ignition switch is moved from the "both" position to either the "left" or "right" position, a slight drop in RPM is typically observed. This occurs because the engine is momentarily running on only one set of spark plugs instead of both, which can result in a small decrease in efficiency and power output. Each ignition system in a multi-engine setup is designed to fire a specific set of spark plugs, and by switching to either "left" or "right," you are excluding one set of plugs. Although the engine should still be able to operate normally, the reduction in the number of ignitions can lead to that slight RPM drop until the engine stabilizes with the remaining operational ignition system. In this context, other options referring to an increase in RPM or significant loss of power would be inaccurate, as the engine is not supposed to experience these extreme responses during operation. There shouldn't be no change in RPM either, as the switch change inherently affects the ignition cycle, leading to the slight drop that is expected.