What Happens When You Switch Engine Ignition from Both to Either Side?

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

• A. Increase in RPM
• B. Significant loss of power
• C. Slight drop in RPM
• D. No change in RPM

Answer: (C)

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.

When you're studying for the FAA Powerplant Written Test, one topic that frequently pops up is the behavior of engines when switching the ignition from the "both" position to one side. So, what’s the deal with this? Well, when you make this switch, you’ll likely notice a slight drop in RPM—yes, just a little tick down. You might wonder why that happens. It’s all about how the ignition system is designed and how it operates.

In a multi-engine setup, each engine has multiple spark plugs to ignite the fuel-air mixture. When you switch the ignition to either the "left" or "right" position, you’re essentially telling the engine to rely on just one set of spark plugs instead of both. That’s like taking away half the candles on your birthday cake—there's still some light, but it’s not as bright! This momentary change does lead to a small dip in the engine’s efficiency and, consequently, its power output.

Now, here’s the good news: although there’s that tiny RPM drop, the engine should continue to work normally without any panic. It's as if you’re putting on one shoe—you're still able to walk, but maybe not as smoothly as with both shoes on! The engine stabilizes pretty quickly with the operational ignition system still firing away.

But hold up—let’s address the other choices you might see. An increase in RPM? That’s like expecting the wind to blow your plane higher just because you opened a window—doesn’t quite work that way! A significant loss of power? Well, that's just not what happens in this scenario if everything’s functioning correctly. And if you think nothing changes in RPM, remember that electrical systems and ignition cycles are sensitive; that switch flip isn’t just a benign act.

As a budding pilot or engineer prepping for a test, grasping these nuances can make a huge difference. After all, understanding how your aircraft operates under various conditions is just as important as knowing how to read a checklist or respond in emergencies. Keep these details top of mind while you study, and you’ll be one step closer to acing that FAA Powerplant Written Test.