During an engine run up, what is the maximum allowable RPM drop for a magneto check?

A magneto check during an engine run-up is a crucial part of pre-flight procedures as it helps ensure the proper functioning of the aircraft's ignition system. The allowable RPM drop during this check indicates how well the magneto systems are performing.

When performing a magneto check, the maximum allowable RPM drop is typically set at 150 RPM for most general aviation aircraft. This threshold is important because a drop beyond this limit can signify an issue, such as a faulty magneto, poor electrical connections, or problems with the ignition system. By adhering to this standard, pilots can ensure that both magnetos are functioning effectively and that the engine will operate reliably during flight.

This understanding is essential for maintaining safety and performance during flight operations. If the RPM drop exceeds this limit, further investigation is needed before taking off, underscoring the importance of this check in the pre-flight inspection routine.