Flight with Slats/Flaps extended at altitudes above which value is prohibited?

• A. 10,000 Feet
• B. 15,000 Feet
• C. 20,000 Feet
• D. 25,000 Feet

Answer: (B)

High-lift devices like slats and flaps are designed for takeoff and landing, not for stable cruise. When you climb to higher altitudes, the air is thinner, so the extra drag from extended slats or flaps becomes a bigger penalty and provides little useful lift. The flight envelope and certification assume a clean configuration in cruise to maintain appropriate climb and cruise performance, energy management, and handling margins. Therefore there is a prohibition on keeping slats/flaps extended above that altitude, which is why the limit is set at 15,000 feet. The other altitudes don’t match the certified limit, so they aren’t the correct restriction.