ILS Glideslope Speed RNAV

For ILSILS —Instrument Landing System glideslope speed questions, there are three methods to solve the problem:

  1. Use trigonometry. This gives the most accurate answer, but is time consuming and requires converting between knots and feet per minute — a difficult conversion, and easy to get wrong.
  2. Use RA=60DRA = 60D. This is slightly quicker and slightly less accurate, but also requires converting units.
  3. Know that on a 3° glideslope, your rate of descent in feet per minute is 5 times your groundspeed. This is the fastest and most efficient way.

Note that if you are given a TASTAS —True Air Speed, you must first apply a head or tailwind correction.

To use the fastest and most efficient method:

  1. Multiply your groundspeed by 5.
  2. Multiply the answer by your actual glideslope.
  3. Divide by 3.

This will give you your rate of descent in knots.

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What approximate rate of descent is required to maintain a 4.5° glideslope at a speed of 189 kts?
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