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If you want to follow a 3.25° glideslope (ILS), when TAS is 130 kt and wind component is 15 kt tailwind, your rate of descend must be:
  • A
    510 feet/min
  • B
    675 feet/min
  • C
    748 feet/min
  • D
    832 feet/min

Calculate rate of descent (ROD) on a given glide-path angle or gradient using the following rule of thumb formulae:

  • ROD (ft/min) = GP° × GS (NM/min) × 100
  • ROD (ft/min) = GP % × GS (kt)

Using the first formula, we will get:
ROD (ft/min) = 3.25 x (145/60) x 100
ROD (ft/min) = 785 ft/min

The precise calculation is:
ROD (ft/min) = Tan (3.25º) x GS (kt) x 6080/60
ROD (ft/min) = 834 ft/min

The results obtained from the rule of thumb (first formula used) are usually slightly lower than reality. Unfortunately, in this case, there is a big gap between the results obtained. On multi-choice answers, choose the higher option if calculating using the first formula only.

Note: This question was seen in a Performance exam. However, there is no matching to this question under 032. Please contact us if you come across this question.

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