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briansommers

how do I compute this?

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I know this is easy, but I'm having a hard time wrapping my head around it given: I have a distance of 3nmI need to descend 900 feet within those 3nmI'm traveling at 100KIAS what is my fpm descent?


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I have a distance of 3nmI need to descend 900 feet within those 3nmI'm traveling at 100KIAS what is my fpm descent?
First you have to convert your KIAS to KTAS. Then you have: at a speed of 100 KTAS, to travel 3nm it takes 3/100 hours = 3/100*60 minutes = 1.8 minutes. So your vertical speed must be 900 feet / 1,8 minutes = 500 fpm. Marco

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No, you have to know ground speed. KTAS won't help you.


Chris Miller

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No, you have to know ground speed. KTAS won't help you.
For practical reasons, yes and no. If you are flying a jet at FL300, yes; if flying a single engine at 8500ft hmm, not so much, the difference would be negligible. Murmur's explanation sounds about right (and you could, again, skip the conversion to TAS if flying low level on a low speed aircraft, it's just a 4 or 5 knot correction anyway)

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For practical reasons, yes and no. If you are flying a jet at FL300, yes; if flying a single engine at 8500ft hmm, not so much, the difference would be negligible. Murmur's explanation sounds about right (and you could, again, skip the conversion to TAS if flying low level on a low speed aircraft, it's just a 4 or 5 knot correction anyway)
With a 30 knot headwind, the difference isn't so negligible... Small plane or not. Or 60 Knots like I had last week with the cold front passage... to the OP, Marco is correct except you need to know ground speed.

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With a 30 knot headwind, the difference isn't so negligible... Small plane or not. Or 60 Knots like I had last week with the cold front passage... to the OP, Marco is correct except you need to know ground speed.
Well, I talk from my experience. Flying here in South America, I've never come across a 30-knot headwind at 8000ft, that's why I make it negligible. Perhaps there are several places where you could find those wind speeds at those altitudes, but I'm unaware of them. Your remark is spot on, nevertheless

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Is South America the land with no winds? We regularly have winds +30 knots 9000 ft and above.


Chris Miller

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