Your
approach ground speed is one hundred knots and you want to maintain a
three degree glide slope. What should your vertical speed be in feet
per minute? (Use Pi = 3, and 1 NM = 6000 ft.)
Ans: 500 fpm
This is a two part problem. First
convert the ground speed into the desired units of ft/min. One hundred
knots is six hundred thousand feet in sixty minutes. (10,000 fpm)
Next
convert 3 degrees to radians: Three degrees is 1/60th of 180 degrees.
(180 deg = Pi radians) One sixtieth of Pi is approximately 1/20 rad.
For
small angles, the sine, the tangent, and the angle in radians converge.
Multiplying the horizontal ground speed and the glide slope in
radians: 10,000 fpm X (1/20 rad) = 500 fpm.
(Since
three degrees is the standard ILS glide slope, we don’t have to do the
math from scratch each time. Just divide your ground speed in knots by
two and then tack a zero on the end.)
