What is the enroute use status of slats and flaps?

The enroute use status of slats and flaps on the CRJ 900 is prohibited during normal operations. This means that once the aircraft is in the cruise phase of flight, the slats and flaps should not be actuated or extended. The design of the aircraft assumes a clean configuration during enroute segments, maximizing aerodynamic efficiency and performance.

By prohibiting the use of slats and flaps enroute, the aircraft is able to maintain optimal fuel efficiency and performance characteristics. Extending these high-lift devices in cruise can lead to increased drag, reduced fuel efficiency, and unnecessary stress on the aircraft's systems. This limitation is in place to ensure safe and efficient flight operations while the aircraft is at altitude.

The other options suggest various allowances for slats and flaps that do not align with the operational design and safety protocols established for the aircraft, which is why they do not apply in this context.