Which device, when deployed, adds to rate of descent without increasing airspeed?

• A. Rudder
• B. Elevator
• C. Ailerons
• D. Flaps

Answer: (D)

The key idea is that you want to increase drag without forcing a rise in airspeed. Extending the flaps changes the wing shape to produce more lift at lower speeds, but it also adds significant drag. That extra drag makes the airplane lose altitude more quickly for the same forward airspeed, so you can descend steeper (increase rate of descent) without increasing airspeed. The other controls mainly affect attitude or direction: the rudder alters yaw, the elevator changes pitch (and speed/ climb or descent), and the ailerons roll the aircraft. None of these primarily provide the drag increase needed to raise descent rate without changing airspeed, so flaps are the device that best fits this situation.