At what RPM is a Magneto "dead cut" check carried out?

The correct moment to carry out a magneto "dead cut" check is during the ground warm-up RPM. This procedure is performed to ensure that the magneto is functioning correctly and can be safely relied upon during flight operations. Performing the check at ground warm-up RPM allows the technician to observe the engine's response to the magneto being turned off, which helps in diagnosing any potential issues while the engine is still in a controllable and safe environment.

Carrying out the check at higher RPMs, such as reference or take-off RPM, could produce higher loads and potentially mask problems that might be observable at a lower RPM. Additionally, during the "mag. drop" check, the focus is typically on measuring the RPM drop between the two magnetos rather than ensuring one magneto's complete failure. Thus, the ground warm-up RPM is preferable for the safety and integrity of the magneto check.