In normal flight, movable slats are closed; they extend to delay separation at high angles of attack. When is a movable slat typically extended?

• A. During takeoff
• B. During landing
• C. In normal flight
• D. During high-speed cruise

Answer: (C)

Movable slats are leading-edge devices that extend to change the wing’s shape and energize the airflow over the wing when the airplane would otherwise reach a high angle of attack and begin to stall. By increasing camber and helping the flow stay attached, they provide extra lift at lower speeds.

Because of the extra drag they introduce, slats are retracted in normal, clean cruise to keep efficiency high. They are extended when more lift is needed at high angles of attack—that happens during high-lift phases such as takeoff and landing (and during go-arounds if necessary). So, the typical time to extend movable slats is during takeoff or landing, not during normal flight.