At what speed do the flaps begin to extend on a Cessna 172?

The correct choice for when the flaps begin to extend on a Cessna 172 is the flap extension speed. In this context, flap extension speed refers to a specific speed threshold defined in the Pilot's Operating Handbook (POH) for the aircraft.

Flaps are primarily designed to enhance lift and decrease stall speed at lower speeds; therefore, they should not be extended too close to stall conditions. When operating the aircraft, extending the flaps at too low of a speed could lead to aerodynamic issues, including potential stalling because of the increased drag.

Typically, the flap extension speed is indicated in the airspeed limitations section of the POH, and the pilot is advised to stay within this speed margin for the safe deployment of flaps. The concept of extending flaps too early or too late can compromise the safety and performance of the airplane. By adhering to the correct flap extension speed—rather than an arbitrary distance above or below stall speed—pilots ensure safe and effective control of the aircraft during critical phases like takeoff and landing.