Under what conditions should the TO DATA SET MENU on the MCDU be set to ALL?

Setting the TO DATA SET MENU on the Multi-Function Control Display Unit (MCDU) to ALL is crucial during specific temperature and moisture conditions to ensure the aircraft performs optimally for takeoff. When the Outside Air Temperature (OAT) is below 5°C and there is visible moisture, this setting helps to account for the potential effects of cold weather on aircraft performance.

In such conditions, frost, ice, or other contaminants can form on the wings, impacting lift and aerodynamic performance. Therefore, selecting ALL in the TO DATA SET MENU prompts the aircraft systems to incorporate additional safety parameters associated with cold weather operations into their takeoff performance calculations. This ensures that the pilots are fully aware of the required takeoff performance benchmarks, taking into account any adverse weather effects that could compromise the safety and efficiency of the flight.

This practice is aligned with aviation safety protocols, particularly in winter operations, where temperature and moisture can pose significant risks if not adequately addressed. By following these guidelines, flight crews can maintain safe operational standards while managing the complexities associated with varying environmental conditions.