Before a magneto check, what safety procedure is normally performed during engine run-up?

Setting the mixture to rich before conducting a magneto check during engine run-up is an important safety procedure because it optimizes engine performance and ensures proper fuel-air mixture for combustion. When the mixture is rich, the engine receives a higher concentration of fuel relative to air, which helps in ensuring that the engine runs smoothly at the higher RPM settings used during the run-up check. This is crucial because a lean mixture could lead to rough engine operation or even engine failure when checking the magnetos.

During the magneto check, the pilot assesses the performance of each magneto by switching between the left, right, and both settings. A good running engine with a rich mixture provides a more accurate indication of magneto performance. If the engine is set poorly, it may not reveal potential issues that could arise from a malfunctioning magneto.

Other choices, while relevant to flight safety, do not address the specific needs of conducting an effective magneto check during the engine run-up.