When should the TO DATA SET MENU on the MCDU be set to ENG?

The correct choice highlights the importance of setting the TO DATA SET MENU on the MCDU to ENG when the outside air temperature (OAT) is between 5-10°C and there is visible moisture. This action is crucial because, during takeoff, the potential for engine performance degradation due to icing can significantly increase when the air temperature is within that specific range and moisture is present.

In these conditions, the engines may be at risk of ingesting ice particles, which could lead to a reduction in performance or even engine failure if not properly managed. Selecting "ENG" in the TO DATA SET MENU configures the aircraft to account for the necessary thrust adjustments and engine parameters to ensure a safe ascent while maximizing performance under potentially hazardous conditions.

This approach reflects best practices for safety and performance management during flight operations under varying meteorological circumstances.