What is the maximum difference allowed between left and right magneto RPM?

The maximum difference allowed between the left and right magneto RPM is 50 RPM. This standard is established to ensure that both magnetos are functioning properly and providing sufficient spark to the engine cylinders, which is crucial for smooth operation and reliability of the aircraft.

When conducting a magneto check during pre-flight procedures or engine run-ups, the pilot observes the RPM drop when each magneto is tested. A difference larger than the specified limit may indicate a problem with one of the magnetos, such as a faulty spark plug or other ignition system issues. Ensuring the difference stays within this limit not only enhances engine performance but also ensures safety during flight operations, as an engine running on one faulty magneto could lead to a failure in flight. Thus, maintaining a maximum allowable difference of up to 50 RPM is a critical aspect of proper flight preparation and aircraft maintenance.