This approach is executed by gliding with the power off from a given point on a downwind leg to a preselected landing spot (Fig. 9-28). Actually it is an extension of the principles involved in the 90 degree power off approach just described. Its objective, then is to further develop judgment in estimating distances and glide ratios, in that the airplane must be flown without power from a higher altitude and through a 90 degree turn to reach the base leg position at a proper altitude for executing the 90 degree approach. Consequently, the 180 degree approach requires more planning and judgment than does the 90 degree approach.
In the execution of 180 degree power off approaches, the airplane is flown on a downwind heading parallel to the landing runway and the landing gear extended (if retractable). The altitude from which this type of approach should be started will vary with the type of airplane, but it should usually not exceed 1,000 feet above the ground, except with large airplanes. Greater accuracy in judgment and maneuvering is required at higher altitudes.
When abreast of or opposite the desired landing spot, the throttle should be closed and altitude maintained while decelerating to the manufacturer's recommended glide speed, or 1.4 Vs0. The point at which the throttle is closed is the "downwind key position."
The turn from the downwind leg to the base leg should be a uniform turn with a medium or slightly steeper bank. The degree of bank and amount of this initial turn will depend upon the glide angle of the airplane and the velocity of the wind. Again, the base leg should be positioned as needed for the altitude, or wind condition; that is, position the base leg to conserve or dissipate altitude so as to reach the desired landing spot.
The turn onto the base leg should be made at an altitude high enough and close enough to permit the airplane to glide to what would normally be the base key position in a 90 degree power off approach.
Although the "key position" is important, it must not be
overemphasized nor considered as a fixed point on the ground. Many inexperienced
pilots may gain a conception of it as a particular landmark such as a tree,
crossroad, or other visual reference, to be reached at a certain altitude.
This will result in a mechanical conception and leave the pilot at a total
loss any time such objects are not present. Both altitude and geographical
location must be varied as much as is practical to eliminate any such conception.
After reaching the base key position, the approach and landing are the
same as in the 90 degree power off approach.