# How to calculate a 2º descent?

Here is explicitly a question had in mind for a very, very long time.I asked some member on the community and, from all the people I asked no one could have given me their belief on a formula I could use so, i decided to ask the public IFC (infinite flight community.So here is what I have.

TOD-distance/2,-10,/3,1000*=cruise.
Another formula I have is total distance /7=F.L.*1000=Cruise Alt.

Sorrys for disturbing the peace.
Cheers xfriend.

Where’s the question?

4 Likes

… wat?
Maybe explain what this is?

I’m not even good with common core geometry yet and you ask this??? Like a foreign language

2 Likes

Instead of a standard 3º rate, what about descending from. Cruise to airport elevation on a 2º rate?

Guessing that you’re asking for a formula to calculate a slower and smoother descent, I give you this:

Distance from destination when you should start descent = (FL / tan x)

Take any value for x from 0° to even 90°. The less the angle, the smoother is the descent and so is the distance to begin descent.

Never mind if this isn’t what you’re looking for!

1 Like

thank god someone finally gets what I mean,“Guessing that you’re asking for a formula to calculate a slower and smoother descent.”

3degrees descent=5.19X to equal v/s
2degrees descent=3.46
X to equal v/s for a descent.

Have a good time! 👌🏼

If your cruising altitude was [altitude]ft, using the formula: tan(2)=[altitude]/x, x would return the distance at which you need to start descending (in feet, you probably want to convert to nm). After you get the NM at which you need to descend, you need to calculate your VS. To do that use, time=distance/speed. Time will equal your ETA. Altitude/time (in minutes) will return your VS.

Example:
Altitude = 30000ft
Speed = 300kt GS

tan(2)=30000/x; Where x=remaining feet.
x=860000
860000ft to nm equals about 150 NM.

time= distance/speed
x = 150/300

At 30 minutes out, you must start your descent.

Altitude/time=VS

30000/30=1000fpm.

At 30000ft going 300kt GS, you must start your descent 150nm out and go at -1000fpm to have a descent angle of 2 degrees.

So…, the relationship is as angle increase, v/s decrease?

Your currently explaining a time descent right?
Example.cruise FL200 20mins. start descent as 1000v/s

Now you’re conflating terminology a bit. The glide path angle for a specific runway isn’t the same as TOD.

2 Likes

If you increase x, you’ll have be descending at faster rate to possibly land.

Hey! A good formula I have is ((Current altitude-target altitude)/Rate of decent)*(KGS/60)=Distance from Target you should begin decent. But for the angle of decent I guess you’d use Tan(angle)=(Current Alt-Target alt)/Distance from Target
Hope this helps!

This thread makes me feel stupid.

like I have no idea how to understand this complicated math

1 Like
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