Which devices are primarily considered lift-decreasing?

Lift-decreasing devices are designed to reduce the lift produced by an aircraft's wings, particularly during specific phases of flight such as landing or when maneuvering at lower speeds. Spoilers and speed brakes serve this purpose effectively by disrupting the airflow over the wings.

When deployed, spoilers create turbulence and increase drag, which reduces the wing’s lift. This allows the aircraft to achieve a controlled descent or to slow down more quickly when necessary, enhancing the aircraft's handling characteristics particularly during approach and landing. Speed brakes achieve a similar effect by increasing drag and lowering lift without significantly altering the aircraft's pitch attitude.

Leading-edge flaps, trailing-edge flaps, and slats, on the other hand, are primarily lift-enhancing devices. They are deployed to increase the wing's surface area and improve its aerodynamic profile, enabling higher liftoff weights and safer stall characteristics at lower speeds. Therefore, they do not fit into the category of lift-decreasing devices.