The following general discussion applies to airplanes equipped with flaps. The pilot may use landing flaps during the descent to adjust lift and drag. Flap settings help determine the landing spot and the descent angle to that spot. [Figure 1 and Figure 2]
Figure 1. Effect of flaps on the landing point |
Figure 2. Effect of flaps on the approach angle |
- Producing greater lift and permitting lower approach and landing speeds,
- Producing greater drag and permitting a steeper descent angle,
- Increasing forward visibility by allowing a lower pitch, and
- Reducing the length of the landing roll.
The time of flap extension and the degree of deflection are related. Large changes in flap deflection at one single point in the landing pattern can produce large lift changes that require significant pitch and power changes in order to maintain airspeed and descent angle. Consequently, there is an advantage to extending flaps in increments while in the landing pattern. Incremental deflection of flaps on downwind, base leg, and final approach allow smaller adjustments of pitch and power and support a stabilized approach.
Whenever the flap setting is changed, the pilot should be prepared to re-trim the airplane as needed to compensate for the change in aerodynamic forces. Throughout the Approaches and Landings section, more detail is provided on the use of flaps during specific approach and landing situations, as appropriate.