Problem with descent calculator

I used a descent calculator to plan my descent but I was way too high before landing. Is there something i’m doing wrong?
Here is what I used:
Here is what I put for every box:

Or another simple way to plan that, is if you’re at FL300 start decent around 15-16 minutes out. At a rate of 2000 Vs. Just Half your cruise ALT, and whatever you number you get, that number would be the time you start decent.
FL300/2=15 min
FL310/2=15 min 30 seconds
FL320/2=16 min

So on and so fourth


What’s so popular with these descent calculators? I can’t wrap my mind around them because they’re dependent on speed, and speed is always varying in your descent. This is most likely why you were too high when you reached your destination. Also, these calculators are not realistic at all - no IRL aircraft descends from cruising altitude down to final in one go. Check FlightAware descent tables for verification.

For me, and being more realistic, it’s easier to know the altitudes to be at by the time you reach a fix/VOR. Following this, it’s simple math to determine your VS given your time and speed on your FPL. For descents over terrain, it’s best to check with SkyVector.

But how do I know at what altitudes I need to be at a certain fix/VOR?

I use FlightAware/Flight Planner/SkyVector to determine my altitudes ahead of time.

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But you don’t see the fixes. I don’t understand how you can do that.

I can see the fixes in the tables/charts.

Most charts say « at or above » at each fix. There is no specific altitude.

Can someone help me!!!

Do you have one with what each field indicates.

Cruise and target altitude can figure out, but what are the others?

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I don’t understand. The other boxes is where you enter your speed.

Yes, so I gathered, but which speeds? KIAS is a lot different from GS.

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I entered the IAS speeds into the calculator.
Here you see what you have to put in each box.

Yeah, don’t use that calculator. It’s caused nothing but trouble for me.

Well, that’s likely the issue.

IAS is a poor indicator of how fast you’re truly tracking across the ground.

When I calculate descent I use GS. Some use TAS.

Essentially to get from cruise to 11000 or 10000, depending on direction of travel, I use the following:

(Altitude to lose * GS) / (V/S * 60) = Distance to lose

Thats if I know my intended V/S. It will give me a distance from my target point to be at 11k or 10k to descend.

Alternatively, and along the way down:

(Altitude to lose * GS) / Distance to Target / 60 = V/S needed to hit target

As @IF515 mentioned, though, your GS will decrease as you descend, so you can either start off at a higher V/S and figure when to make it less steep along the way, or you can calculate for something like 2000, then just use 1800 instead, and again check along the way.

Nothing is perfect, because your GS is always changing. You would need some sort of calculus equation to manage that in one input.

But I do know that you won’t get anywhere close using IAS.


So I use the cruise GS when calculating descent?

GS is how fast you’re actually tracking across the ground, so it’s a better indicator than IAS, since the same airspeed can mean you’re covering all sorts of distances, depending on winds, etc.

You GS at cruise will go down as you descend of course, so you will need to adjust for that, generally making your descent more shallow later on, but it’s a much better speed to use tha IAS.

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Ok, so how do I know when I need to adjust the VS?

I do this along the way, using my current MSL and GS to recalculate the V/S.

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And you also use your current distance to the target?