34 Final Approach Roundout starts Distance Traveled Past Aiming  Point to Touchdown Touchdown Aiming point is  where descent angle  intersects ground Figure 11-18. Stabilized approach. For a constant angle glidepath, the distance between the  horizon and the aiming point remain constant. If a fi nal  approach descent has been established but the distance  between the perceived aiming point and the horizon  appears to increase (aiming point moving down, away from  the horizon), then the true aiming point and subsequent  touchdown point is farther down the runway. If the distance  between the perceived aiming point and the horizon decreases  (aiming point moving up toward the horizon), the true aiming  point is closer than perceived. free to devote full attention to outside references. The pilot  should not stare at any one place, but rather scan from one  area to another, such as from the aiming point to the horizon,  to the trees and bushes along the runway, to an area well  short of the runway, and back to the aiming point. In this  way, the pilot is more apt to perceive a deviation from the  desired glidepath and whether or not the aircraft is proceeding  directly toward the aiming point. When the aircraft is established on final approach, the shape  of the runway image also presents clues regarding what  must be done to maintain a stabilized approach to a safe  landing. A runway is normally shaped in the form of an  elongated rectangle. When viewed from the air during the  approach, perspective causes the runway to assume the shape  of a trapezoid with the far end appearing narrower than the  approach end, and the edge lines converging in the distance.  If the aircraft continues down the glidepath at a constant angle  (stabilized), the image the pilot sees is still trapezoidal but  of proportionately larger dimensions. If the pilot perceives any indication that the aiming point  on the runway is not where desired, an adjustment must be  made to the glidepath. This in turn moves the aiming point.  For instance, if the pilot perceives that the aiming point  is significantly short of the desired touchdown point and  results in an undershoot, an increase in power is warranted.  The minimum airspeed recommended by the manufacturer  must be maintained. This results in a shallowing of the  glidepath with the resultant aiming point moving toward the  desired touchdown point. Conversely, if the pilot perceives  that the aiming point is farther down the runway than the  desired touchdown point and results in an overshoot, the  glidepath should be steepened by an increase in speed with  the throttle at idle. It is essential that deviations from the  desired glidepath be detected early, so that only slight and  infrequent adjustments to glidepath are required. During a stabilized approach, the runway shape does not  change.  [Figure 11-19]  If the approach becomes shallower,  the runway appears to shorten and become wider. Conversely,  if the approach is steepened, the runway appears to become  longer and narrower.  [Figure 11-20] If a situation arises in which the required corrections become  larger (and possibly more frequent) as the aircraft draws closer  to the runway, an unstabilized approach results. Common errors in the performance of normal approaches and  landings include the following: The objective of a stabilized approach is to select an  appropriate touchdown point on the runway and adjust  the glidepath so that the true aiming point and the desired  touchdown point coincide. Immediately after rolling out of  base leg and onto final approach, the pilot should adjust the  speed so that the aircraft descends directly toward the aiming  point. With the approach set up in this manner, the pilot is  •  Not realizing there is a tailwind during downwind to  complete an early base  •  Inadequate wind drift correction on the base leg 11-11