Back to Aircraft Accessory FAQs

Is the Dual Magneto connected to the rest of the electrical system?

No, the Dual Magneto ignition system is independent from the aircraft electrical system. In the event of an electrical failure the mechanical Dual Magneto will continue to provide spark to the engine.

Does the Dual Magneto come with capacitors?

We will provide two new capacitors with the Dual Magneto if you purchase an exchange or have your unit overhauled.

Can I buy a new Dual Magneto?

Currently, no new Dual Magnetos are being produced. You can have your Dual Magneto repaired, overhauled, or exchanged for an overhauled unit.

How do I check Dual Magneto drop?

Dual Magneto operators should be aware of Lycoming Service Instruction 1132B, issued June 18, 2010, which provides a procedure to use if magneto drop exceeds 175 RPM during the pre-flight check. A basic Dual Magneto drop-off check based on engine speed is typically done during the before-takeoff check to determine the loss of engine speed that occurs when magnetos are switched from both magnetos to one (left or right) magneto. The maximum drop-off limit is in the Pilot’s Operating Handbook (POH). Although this basic drop-off check, based on just engine speed, is satisfactory under most normal conditions, it does not take into account unusual circumstances of temperature, humidity and engine wear. If the RPM drop exceeds 175 RPM, set the throttle to obtain 1,800 RPM. Slowly lean the mixture until the RPM peaks. Then retard the throttle back to 1,800 RPM and repeat the magneto drop-off check. If the drop-off does not exceed 175 RPM, the difference between the drop-off values for both magnetos does not exceed 50 RPM, the engine is running smoothly, then the ignition system is operating properly. Return the mixture to full rich.

What does absence of an RPM drop indicate about my Dual Magneto?

The absence of a drop may mean the following for your Dual Magneto:

• The Dual Magneto has been advanced beyond the specified setting
• A Dual magneto primary lead is open (Hot Magneto)
• An ignition switch is inoperative
• The grounding circuit of the feed through capacitor is open, or a combination of the above factors