Under what condition is the use of Slats/Flaps prohibited during flight?

The use of slats and flaps during flight is generally prohibited during enroute phases due to several operational safety considerations. Enroute flight typically involves cruising at higher altitudes and airspeeds where the aerodynamic conditions require a clean wing configuration for optimal performance, fuel efficiency, and handling characteristics. Utilizing slats and flaps, which are designed to increase lift during lower-speed operations (such as takeoff and landing), can lead to aerodynamic instability or increased drag at normal cruise speeds.

This configuration is not only inefficient but can also trigger unwanted increases in drag and the potential for loss of altitude or control. Therefore, strict adherence to the prohibition of slats and flaps while enroute contributes to safer and more efficient flight operations.

In contrast, the other options pertain specifically to phases of flight where slats and flaps are normally used to enhance performance, like during takeoff and landing, or in ascent, where they play a critical role in lift management.