A hot mag refers to a magneto in an engine (typically an aircraft engine) that can discharge its electrical energy even when the ignition switch is in the "off" position.
Understanding Hot Mags
Here's a breakdown of what a hot mag is and why it's important:
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Magneto Function: A magneto is a self-contained ignition system that generates high-voltage electricity to fire the spark plugs in an engine. It does this independently of the aircraft's electrical system.
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P-Leads: Each magneto has a "P-lead" (primary lead) that, when grounded, prevents the magneto from firing. The ignition switch controls the grounding of these P-leads. When the switch is in the "off" position, the P-leads should be grounded, disabling the magnetos.
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The "Hot" Condition: A "hot mag" occurs when the P-lead is not grounded when it should be. This can happen due to:
- Switch Failure: A faulty ignition switch that doesn't properly ground the P-leads.
- P-Lead Failure: A broken or disconnected P-lead wire.
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The Danger: When a magneto is "hot," it can still produce a spark if the engine is rotated. This can happen even with the ignition switch off. Therefore, the engine might start unexpectedly, posing a serious safety hazard, especially when performing maintenance or pre-flight checks where the propeller might be inadvertently turned.
Why Hot Mags Are a Concern
The primary concern with a hot mag is the potential for accidental engine start. This can lead to:
- Propeller Strike: Individuals near the propeller can be seriously injured or killed.
- Damage to Aircraft: Unexpected engine starts can cause uncontrolled movement and potential damage to the aircraft or surrounding objects.
How to Identify and Prevent Hot Mags
- Magneto Check: During pre-flight checks, pilots perform a magneto check to ensure each magneto is functioning correctly and that the engine shuts off completely when the ignition switch is turned to the "off" position. If the engine continues to run (even sputtering) with the switch in the "off" position, a hot mag is indicated.
- Proper Maintenance: Regular inspection and maintenance of the ignition system, including the ignition switch and P-leads, are crucial for preventing hot mags.
- Follow Procedures: Always follow proper procedures for starting and stopping the engine, including verifying that the propeller area is clear before starting.
- Treat Propeller as Always "Live": Even if the engine is off, always treat the propeller as if the engine could start at any moment.
