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5 Answers

Find descent rate after IAF to FAF

Asked by: 2151 views Aerodynamics, Aircraft Systems, General Aviation

Hello, I was trying to find the descent rate after IAF so I can have a smooth descent and be above restriction levels. here are the data. Starting Alt: 6000ft Ending Alt: 3400ft GS: 120knots Distance to travel 14 Dme So I want to find how many feet I need to lose (6000ft - 3400ft) in 14 Dme from the station

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5 Answers

  1. Bruce J. Sato CFI, CFII on Oct 30, 2013

    I’m not certain if this is correct but there’s an equation, i think its on a E6B.

    Speed Distance to loose
    ——— ———————–
    60 Time

    120 knots 14 DME
    ———— ——-
    60 Time?

    You now cross multiply.
    1.) 120 x’s (Time lets call this “x”) = 120x
    2.) 60 x’s 14 = 840
    3.) So now you have 120x = 840

    Now you divide
    120x = 840
    120 120
    x = 7 minutes

    So its going to take 7 min to go 14 DME at 120knots, but wait your not done yet!

    Subtract (6,000′ by 3400′ = 2,600′)
    Divide 2600′ by 7, to get your FPM = 371.42 (371 FPM)

    Total answer:

    So you need to loose 2,600′
    Descend at 120 knots for 7 minutes for a distance of 14 DME at a rate of 371 FPM

    Again I’m not certain of this information and is not a definite answer but hope this helps out.

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  2. Best Answer

    Wes Beard on Oct 30, 2013

    6000 – 3400 = 2600.

    2600 ft / 14 NM = 186 ft / NM

    VSI rate – 186 ft/NM x 120 NM/hr / 60 min/hr = 372 ft/min descent.

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  3. Lion on Oct 31, 2013

    1. GS per minute? ……………………………………12/6 = 2 nm/min (dropped zeros to simplify)

    2. Total time required to cover the 14 nm?……14 / 2 = 7 min

    3. ALT to lose?………………………………………….60-30-4=26 (dropped 2 zeros from each)

    4. 26/7= 371 (the result is 3.71 but use logic to make it 371 ft )

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  4. Brian on Nov 02, 2013

    Ignoring your conditions here is a little cheat cheat for a 3 degree glide path.

    Ground speed * 5 will roughly estimate your decent rate for a 3 degrees. Clean quick and simple. 🙂

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  5. Clark Hall on Mar 02, 2014

    120 * 5 = 600 FPM = 3 degrees
    2600 ft / 300 = 8.6 miles to descend = 3 degrees descent
    So when 8.6 miles from 3400 altitude point start the descent.

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