US AAF TM 1-210: Elementary Flying - Accuracy Approaches

57. General.--The aptitude required when estimating altitude and the distance an airplane will. glide to a landing under varying wind conditions is a matter of visual. perception and depends upon the student's ability to associate the various factors involved. This aptitude is a personal attribute and is developed in proportion to his awareness of surroundings, his powers of observation, and the meaning he gives to observed phenomena as a result of practice and experience.

a. Estimation of distance.--Estimation of distance depends upon experience in comparing the actual size of an object with its apparent size; then perceiving the results in terms of measure, such as feet, yards, or miles. The accuracy of the perception depends upon the experience and aptitude of the observer.

b. Estimation of altitude.--When estimating altitude additional factors, such as the movement of the airplane, absence of intermediate points, distance being measured in a plane vertical to the surface of the earth rather than in the customary horizontal plane, all add to the difficulties in arriving at reasonable conclusions. These factors, plus the student's adjustment to a new environment, cause the process to require considerable time and direction if practical results are to be expected.

(1) With some experience the average person can estimate distances up to 300 or 400 yards with reasonable accuracy but beyond these distances it requires considerable experience and aptitude upon the part of the individual. The same is true when estimating altitude, and with some experience and practice it is possible to estimate altitudes up to about 1,000 feet with fair accuracy.

(2) Proficiency in estimating altitude or applying a unit of measure to altitude is obtained by practice in noting the altitude indicated by the altimeter and observing the apparent size and appearance of objects upon the surface of the earth at the time the altimeter readings were made. Applying this principle, the ability to estimate altitude is developed by association, limited by the perceptual powers of the individual and implies practice in an area where the observed altitude expressed by the altimeter is not at great variance with the actual altitude.

(3) Other than to comply with regulations, the chief concern of the pilot is that his available altitude is sufficient to accomplish his purpose. The information as to altitude in terms of linear measure is not as important as his knowledge of altitude in terms of permissible maneuvering. However, with the student, proficiency in the latter can only be obtained by practice in maneuvering from predetermined altitudes until his perception is developed to the point where he does not give so much attention to his altitude in terms of feet as he does to his altitude in terms of the amount of maneuvering that is possible.

(4) Ability to estimate the distance an airplane will glide is the basis of all power-off accuracy work and determines the amount of maneuvering which may be made from any altitude. This ability is attained through the perception developed by practice and experience. However, in its attainment there are several factors which must be considered.

c. Glides, angle and speed.--(1) One of the first requisites to accuracy in power-off work is the ability to maintain a normal or even gliding speed. Without this ability there can be no accuracy as in all power-off work there are variables which are not under his control, such as drift. If the glide is erratic he is adding to his difficulties as he is unable to dissociate the effect of the wind from the effect of the varying glide and consequently has no basis for maneuvering; his accuracy is a matter of luck and he will be unable to adjust himself to the gliding characteristics of the airplane. Corrections or changes to the normal gliding distance may be made by experienced pilots with certain type airplanes by increasing or decreasing the speed of the glide, but it is not advisable to use this method. An even gliding speed should be emphasized.

(2) Allowance must be made for the distance traveled while reducing the surplus speed to that of gliding, as the glide is not established until this excess is dissipated.

(3) The terms "gliding angle" and "gliding speed" are used indiscriminately and for all practical purposes, once the glide has been established, are one and the same. Each type of airplane has a theoretical angle of best glide. This is expressed as a ratio, such as 6 to 1, and means that the airplane will glide a horizontal distance equal to six times the altitude at which the glide was established. Consequently, part of the perception involved when determining the distance an airplane will glide is angular, as the pilot visually estimates where the angle of glide will strike the ground. If this estimated point is short of his desired objective, unless he has a following wind, he will not be able to glide to it without aid from the engine; if beyond his desired objective, he can glide to it, unless there is a strong opposing wind. For example: A pilot is approaching a field for a landing. He is familiar with the type of airplane he is using and knows approximately how much distance to allow in order to establish his glide; has a visual perception of the angle of glide; makes allowance for the effect of the wind and the distance the airplane will roll after landing. With this preliminary estimate completed, he will retard the throttle when the airplane is in a position such that the angle between him and his objective is that which experience has taught him will enable him to reach it. If he has made too much allowance for these factors, he must slip or "S" and if too little allowance were made, he must "drag" the airplane in with the engine. The same principle applies to forced landings, either actual or simulated. If altitude allows for a choice in the selection of emergency fields, the pilot will first inspect that area which is in the angular relation to him that experience has taught will allow latitude in the maneuvering to a landing, or he will visually apply the angle of glide. His next inspection may be, due to circumstances, of that area near the limit of glide, angularly estimated; then beneath him or to the rear. His decision as to the field selected is based upon his estimate of the distance the airplane will glide, the possible effect of the wind and a margin for errors in maneuvering or estimating wind effect.

(4) Any knowledge of the theoretical angle of best glide, or the gliding ratio of the type of airplane he is using, is valueless to the student until he has developed perception of the gliding characteristics and the distance some one particular airplane will glide. Once he has developed this perception in one type he may quickly adjust himself to one with different characteristics. Then, terms, as used in the foregoing, have meaning to him and he can apply them to practical conditions. Their importance will increase as the speed characteristics of the airplane increase.

d. Effect of maneuvering, (1) With some experience it is not difficult to estimate how far the airplane will glide but this information is valueless unless there is the ability to maneuver and consider the factors involved when maneuvering. Assuming that the altitude is sufficient to permit reaching the landing objective, then the rate of approach and the loss of altitude during the approach determine the amount of maneuvering which may be done and still reach the objective.

(2) At altitudes below 1,000 feet, relative speed and loss of altitude are less difficult to ascertain since they are within normal perceptual powers and objects appear nearer their actual size. From lower altitudes the results may be more accuratel y gaged, especially as the airplane arrives closer to the objective and approaches that altitude and position from which the pilot has had the most experience in landing practice.

(3) With the students ability to estimate the distance an airplane will glide to a landing and the amount of maneuvering which may be done can only be determined by considerable practice and experience in actually maneuvering the airplane under various conditions. With the more experienced pilot, ability in this respect does not require so much practice as he has experience as a basis upon which to make the rapid adjustments necessary.

(4) During flying training the student's proficiency in power-off accuracy is developed as follows:

(a) Considerable practice in maneuvers performed at a constant altitude such that he obtains a visual perception of that altitude.

(b) Landing from predetermined altitudes and positions in relation to a landing objective so that he develops a visual perception of the allowable limits of maneuvering and still reach his objective safely.

e. Training methods to develop essentials of poweroff accuracy work.--The program of flying training is arranged and stipulations made as to the altitude at which various maneuvers will be performed in order to promote an orderly development of the visual perception necessary to insure proficiency in power-off accuracy. The practice of all maneuvers which are required to be performed at a specific altitude, such as elementary eights, rectangular courses, "S's" across a road, and pylon eights have a very material bearing upon this development. Landing from traffic altitude, 90° side approaches for landing, 180° side approaches, 360°, and simulated forced landings from various altitudes are the important training maneuvers whose sole purpose is to develop power-off accuracy. These are explained in the following:

(1) Adaptation of characteristics of airplane, that is, speed, radius of turn, relative movement in relation to the ground, to working altitude at which maneuvers are performed:

(a) The characteristics of the present elementary training airplane are such that the best results are obtained when all elementary eights and allied maneuvers, such as rectangular courses and "S's" across a road are practiced at an altitude of 500 feet. As considerable time is devoted to these maneuvers, the student unconsciously acquires a fair visual picture of this altitude

(b) The altitude at which traffic around the various landing fields operates must be within definite limits in order to assure reasonable safety when approaching the field and when landings and take-offs are being practiced. An altitude of 500 feet is used for traffic as this allows reasonable maneuvering during landing practice and at the same time prevents exaggerated errors of undershooting or overshooting the landing objective- This is the altitude at which elementary eights are practiced and consequently aids in fixing the student's impression of this altitude without constant reference to the altimeter.

(2) (a) The key position is that general position in the air and in relation to a landing objective from which the student has made so many landings that once he is able to maneuver the airplane to it or through it he feels reasonably certain that he will know where the airplane will first strike the ground when landing

(b) This Position is not a definite geographical point but a general position, and in all power-off accuracy work, other than low altitude forced landings, the student attempts to maneuver to this location. However, when explaining the key position it must not be stressed to the degree that the main objective--landing in the field selected--is lost sight of, as it is an intermediate point or a means to accomplish an end and not the end itself. If overstressed it becomes more difficult to reach the key position than it is to reach the landing objective.

(c) The development of the student's key position commences when he first starts landing practice and is based upon the following:

1. He is required to retard the throttle at an altitude of approximately 500 feet, to the leeward and to one side of his landing objective. The landing is made from a 90° gliding turn. During landing practice he will spend considerable time gliding into a field from this one general position. Consequently this aids in fixing his impression of this altitude and position in relation to a landing objective as well as the limitations of maneuvering from this altitude and position.

2. When landing from a straight approach, the pilot may easily estimate how fast he is approaching the field but has a poor conception of the loss of altitude commensurate with this approach as he is able to estimate his position in relation to one dimension only--forward. As a general rule this method is used only when power is available or the landing objective is near the extreme limit of glide and the situation affords no opportunity for maneuvering. In addition to causing difficulty in the estimate of the relative loss of altitude, such an approach leaves much of the field obscured with the possibility of striking an obstacle which had not been observed during the preliminary inspection of the field.

If the pilot lands from a gliding turn, not necessarily at right angles to the direction of landing, he is able to note the rapidity of his approach to the field, relative loss of altitude, and the effect of drift due to wind. Based upon the information so obtained, he may increase or decrease the radius of turn he is using and thus reach his landing objective with the minimum of difficulty. Varying the radius of turn to fit the situation is termed "playing the turn" and ability in this respect assures reasonable accuracy in power-off work without the necessity of constant practice to maintain proficiency.

58. 90° approach (fig. 8) --This approach is executed from the standard rectangular course around a landing field. Specific instructions and practice should be given in order to aid the student in landing in a designated area of the landing field. It should be thoroughly explained to the student that deviation from a normal glide or incorrect use of flaps in order to land in a designated area will result in a less satisfactory grade than failure to land in this area if use of the glide and flaps is normal.

59, 180° side approach (fig. 9), -a. Purpose.--The purpose of this approach is to impress upon the student the limitations and amount of maneuvering which can be done from this altitude and still safely reach the designated landing area. It brings out the important factor that a pilot cannot with impunity fly away from his landing area and still safely reach it. It is an approach which can readily be adopted, with slight variations, in a majority of forced landings

b. Execution.--This approach is performed from an altitude of 800 feet to the side of the landing field and at such a distance as to enable maneuvering and landing in the designated landing area. The throttle should be retarded and glide established opposite the designated landing area, The first gliding turn should be completed at approximately 500 feet and in the vicinity of the key position for a normal 90° approach.

60. 360° overhead approach g. 1 -a. Purpose. The purpose of this approach is to familiarize the student with a method of maneuvering as to land directly beneath the airplane if sufficient altitude is available- This approach is desirable in that it requires perfect timing, coordination, maintenance of proper, gliding angle and speed, ability to concentrate on ground objects while flying correctly and. to land accurately in a designated landing area,

b. Execution. --This approach is performed from an altitude of' 1,000 feet in the landing direction And with the designated landing area directly beneath.

61. Power-on approach (fig. 11).--a. Purpose-The normal method of approach for landings on unfamiliar landing areas, over obstacles, when operating airplanes with which the pilot is unfamiliar and when piloting heavy aircraft for all landings is the poweron approach or a combination of power-on and poweroff approach. Upon the attainment of satisfactory proficiency in all power-off approaches by a student at elementary flying schools, a power-on approach stage is valuable in rounding out his general flying knowledge and will prepare him more adequately for basic flying training.

b. Execution-(1) Initial practice and instruction should be given at considerable altitude and the student should be encouraged to check his descent by means of the altimeter and to compare it with his rate of descent in a normal glide. The tendency of the student at first will be to close the throttle entirely and then open the throttle too much when the airplane begins to settle. The student should be taught to maintain an approximately even throttle setting, controlling the rate of descent by use of throttle and elevators. The speed should remain approximately constant. Approximately one-half flaps should be used on the straight approach as in a landing without power.

(2) It is recommended that the rectangular pattern be used for the power-on approach stage. The number 4 leg of the rectangle should be sufficiently far back of the assigned landing area so as to require a fairly long power-on approach with sufficient time for minor corrections. The throttle should be partially closed on the number 4 leg, the 90° turn toward the assigned landing area made and flaps lowered. Corrections in rate of descent, forward speed, and gliding angle will be made from this point to the landing area. If the student has judged correctly his forward speed and rate of descent the throttle should be retarded fully just prior to landing.