Which flap setting is acceptable for CAT II approach and landing?

For a CAT II (Category II) approach and landing, the use of flaps is critical as it affects aircraft stability and performance during the approach phase in low visibility conditions. Flaps 5 is the correct setting as it provides an appropriate balance of lift and drag, contributing to improved handling characteristics and control authority at lower speeds necessary for a safe landing.

Flaps 5 allows the aircraft to achieve an optimal configuration, ensuring that descent rates and landing speeds meet operational safety requirements. Additionally, it aligns with the aircraft's operational limitations and certification for CAT II approaches. Other flap settings, such as Flaps 1, Flaps 15, and Flaps 20, either do not provide adequate lift or increase drag too much, which could hinder performance and safety during critical phases of flight like an approach and landing in reduced visibility conditions. Using Flaps 5 strikes a suitable compromise, making it the standard and acceptable choice for CAT II operations.