If one magneto fails in flight, the aircraft engine will typically continue to run, but its performance will be significantly degraded. This is because most piston aircraft engines are equipped with a dual ignition system, meaning each cylinder has two spark plugs, each fired by a separate magneto. This redundancy enhances reliability and ensures more complete combustion.
Immediate Impact on Engine Performance
When one magneto fails, the engine transitions from running on a dual ignition system to a single ignition system.
- Rough Running: The most common symptom is the engine running noticeably rough. This occurs because the remaining magneto is firing only one spark plug per cylinder, leading to less efficient combustion and potentially "missing" on one or more cylinders.
- Reduced Power Output: With only one magneto providing ignition, the engine will not produce as much power as it normally would. Pilots will observe a significant drop in RPM (Revolutions Per Minute) for a given throttle setting.
- Potential Engine Stoppage: In some severe cases, if the remaining magneto is also weak, or if the engine condition is already marginal, the engine might stop running entirely, though it is more common for it to just run rough and lose power.
Dispelling Common Misconceptions
It's important to understand what a single magneto failure does not typically cause:
- No Explosive Failure: Losing a magneto will not cause the engine to blow up, explode, or suffer catastrophic structural damage.
- No Mechanical Damage: It will not send a valve through the engine or cause a cylinder head to blow off. The issue is with ignition, not mechanical integrity.
Summary of Effects
| Effect of One Magneto Failure | Description |
|---|---|
| Engine Running Rough | Less efficient combustion due to only one spark plug firing per cylinder. |
| Reduced Power | Significant decrease in available engine horsepower and RPM. |
| Potential Stoppage | Less common, but possible if the remaining magneto is also compromised or engine is marginal. |
| No Catastrophic Damage | The engine will not explode or suffer mechanical failure due to magneto loss. |
Pilot's Response and Safety Considerations
Upon recognizing a magneto failure (often identified by a sudden drop in RPM and rough engine operation), a pilot's primary action is to manage the situation safely. This typically involves:
- Verifying the Failure: Checking the magneto switch to ensure it's not simply an incorrect setting and confirming which magneto is performing poorly.
- Switching to the Good Magneto: Operating the engine solely on the functioning magneto.
- Adjusting Power Settings: Reducing power as needed to maintain smoother operation, if possible.
- Landing Safely: Planning and executing a landing at the nearest suitable airport, as the engine's reliability and performance are compromised.
Understanding the function and redundancy of an aircraft's ignition system, as explained in resources like the FAA's Pilot's Handbook of Aeronautical Knowledge, is crucial for safe flight operations.
