After the base-to-final approach turn is completed, the longitudinal axis of the airplane is aligned with the centerline of the runway or landing surface so that drift (if any) is recognized immediately. On a normal approach, with no wind drift, the longitudinal axis is kept aligned with the runway centerline throughout the approach and landing. (The proper way to correct for a crosswind is explained under the section, Crosswind Approach and Landing. For now, only an approach and landing where the wind is straight down the runway are discussed.)
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After aligning the airplane with the runway centerline, the final flap setting is completed and the pitch attitude adjusted as required for the desired rate of descent. Slight adjustments in pitch and power may be necessary to maintain the descent attitude and the desired approach airspeed. In the absence of the manufacturer’s recommended airspeed, a speed equal to 1.3 VSO should be used. If VSO is 60 knots, the speed should be 78 knots. When the pitch attitude and airspeed have been stabilized, the airplane is re-trimmed to relieve the pressures being held on the controls.
A stabilized descent angle is controlled throughout the approach so that the airplane lands in the center of the first third of the runway. The descent angle is affected by all four fundamental forces that act on an airplane (lift, drag, thrust, and weight). If all the forces are constant, the descent angle is constant in a no-wind condition. The pilot controls these forces by adjusting the airspeed, attitude, power, and drag (flaps or forward slip). The wind also plays a prominent part in the gliding distance over the ground [Figure 8-2]; the pilot does not have control over the wind but corrects for its effect on the airplane’s descent by appropriate pitch and power adjustments.
Considering the factors that affect the descent angle on the final approach, for all practical purposes at a given pitch attitude there is only one power setting for one airspeed, one flap setting, and one wind condition. A change in any one of these variables requires an appropriate coordinated change in the other controllable variables. For example, if the pitch attitude is raised too high without an increase of power, the airplane settles very rapidly and touches down short of the desired spot. For this reason, never try to stretch a glide by applying back-elevator pressure alone to reach the desired landing spot. This shortens the gliding distance if power is not added simultaneously. The proper angle of descent and airspeed is maintained by coordinating pitch attitude changes and power changes.
The objective of a good, stabilized final approach is to descend at an angle and airspeed that permits the airplane to reach the desired touchdown point at an airspeed that results in minimum floating just before touchdown; in essence, a semi-stalled condition. To accomplish this, it is essential that both the descent angle and the airspeed be accurately controlled. Since on a normal approach the power setting is not fixed as in a power-off approach, the power and pitch attitude are adjusted simultaneously as necessary to control the airspeed and the descent angle, or to attain the desired altitudes along the approach path. By lowering the nose and reducing power to keep approach airspeed constant, a descent at a higher rate can be made to correct for being too high in the approach. This is one reason for performing approaches with partial power; if the approach is too high, merely lower the nose and reduce the power. When the approach is too low, add power and raise the nose.