What is the function of the speed brake on an aircraft?

The function of the speed brake on an aircraft is primarily to change lift and drag. Speed brakes, also known as air brakes, are deployed to increase drag significantly without greatly affecting lift. When activated, they create additional aerodynamic resistance, which helps to reduce the aircraft's speed during descent and landing phases without a substantial alteration in its attitude or angle of incidence.

In practical terms, this allows pilots to control their speed more effectively, particularly in busy airspace or when preparing for landing. By increasing drag, speed brakes contribute to a more controlled and safer approach. In contrast, options related to thrust, yaw, and pitch do not accurately describe the primary purpose of speed brakes. Thrust is managed by the engines, yaw is controlled through the rudder, and pitch is affected by the elevator and control surfaces, making it clear that the speed brake's primary intention is related to the adjustment of drag and, to a lesser extent, maintaining some lift characteristics for effective speed control.