triangle CBD, tan B = 1,250/10,000, or 0.125000;therefore, angle B measures 7°7´30´´. Determining thedistance from the dotted line to the edge of theapproach zone at any station is similarly a simpleright-triangle solution. Suppose that AB is located atstation 0 + 00. Then at station 1 + 00, the distancefrom the dotted line to the edge of the approach zoneis 100 tan 7°7´30´´, or 12.5 feet; therefore, the distancebetween the center line and the edge of the approachzone at this station is 750 + 12.5, or 762.5 feet.To check for obstructions, you must setup a transitat the narrow end of the approach zone, set thetelescope at a vertical angle equal to the one that theglide plane makes with the horizontal, and takeobservations over the whole approach zone, asindicated in figure 10-27. Determining the verticalangle is a simple right-triangle solution. If the glideangle is 50:1, then the tangent of the vertical angle is1/50, or 0.020000, and the angle measures 1°8´45´´.Figure 10-27 shows how the exact verticallocation of the glide plane varies with the character ofthe surface of the end zone.WATERFRONT SURVEYSUnder some circumstances it is possible to chaindistances over the water; however, it is usually moreFigure 10-27.—Approach clearance for different types of end zones.10-26
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business