Good Descent Calculator.


#1

I am looking for a decent calculator that will give me the right measurements also needs to have a above 10000 and below 10000 feet airspeed with it.this is what I am using right now. https://x-planetools.com/descent.html


#2

@Daniel14 has an equation for that. He says it works every time (forgot what it was tho 😬)


#3

Basically, you take 100 and add the first 2 numbers of your altitude and subtract the height of your airport and descend at -2000 has never failed me before
So if you at 35,000ft and your airport is 2,000ft, take 35 for the altitude add 100 and subtract 2 for the height of the airport and you get 133nm


#4

As a heads up, you might want to correct the title to “Descent” :)


#5

Hello!

To achieve a 3º descent rate you must multiply your ground speed by 5.2. Eg. You’re travelling at 500knots (ground speed). 500 x 5.2 = 2600. You should descend at 2600 feet per minute to achieve a 3º descent speed.

Note: as IF does not have a Flight Path Angle (FPA) option, you must monitor your ground speed and change vertical speeds as required. See the below table to assist in this.

Ground Speed (knots) 3º Descent angle (ft/min)
96 500
115 600
134 700
153 800
173 900
192 1000
211 1100
230 1200
250 1300
269 1400
288 1500
307 1600
326 1700
346 1800
365 1900
384 2000
403 2100
423 2200
442 2300
461 2400
480 2500
500 2600
519 2700
538 2800
557 2900
576 3000
596 3100
615 3200

Knowing when to commence decent for a 3º descent angle is very easy to work out! Take your current flight level, subtract the flight level you wish to end at and divide by 3. For example, to descend from FL410 to FL30, (410-30) = 380. 380 / 3 = 126.667. That means you’ll require 126.667 nautical miles to descend to FL30 from FL410.

Ensure you take into consideration the altitude of the destination airport and ensure you take into consideration the final 3000 ft. Eg. To descend from FL410 to FL30, you must allow an additional 10 nm to depend from 3000’ to 0. It is always a good practice to add a few extra nm on to the descent rate to ensure you’re at the desired altitude on time.

Hope this trick was helpful.

Regards,
@Transport_Hub


#6

Thanks for this. Good tip.
After my Android upgrade, my clever little app didn’t work anymore.


#7

For a routine descent the information given above is enough. But if you want to get technical with geometry, I’d suggest to check out the topic below:


#8

I use flight level x 3 for TOD determination. Example would be cruise at FL300 would give you a TOD of 90nm from destination. For descent rate, I use ground speed x 5. Example 500kts GS would equal -2500 FPM descent rate. Adjust descent rate as ground speed decreases. I maintain cruise Mach level in descent until autopilot reverts to knots < FL280 at which point I maintain 300kts. At FL180 I reduce to 280kts and at FL130 I reduce to 240kts. At FL100 you should be 30nm from destination. At 25nm from dest. I reduce to 220kts and at 15nm I reduce to 190kts, adding flaps if necessary, maintained until established on localizer. This allows me to have a fairly standaradized approach and descent process. Obviously, break from this and follow ATC directions when available.


#9

If you don’t want to do the whole calculation in the head (Like me), which usually isn’t completely precise either. I use to steps.
First I find my TOD (Top of Descend) by multiplying my altitude (35000=35) times 3. If we take in account 35000ft as my cruising altitude, you multiply 35x3=105. You then add 10 (As you wanna be at your target altitude (3000ft AGL ish) 10nm out. And then you add a little (10-20) or whatever you feel is necessary. In this case, and with an added 10 to the equation, the result is 125. Thus, you’ll be descending once you reach 125nm remaining on your flight plan.

As you now know your TOD, you can simply plot it into the calculator linked below, and a along with a speed (again, whichever you feel is suitable for your flight) you plot your cruise altitude, TOD point and target altitude, and simply hit “compute”
http://aerotexas.com/desplan/desplan.php

May be confusing, Let me know if you have any questions!


#10

i just decend at 120nm at 35000 with vs-1800
and speed 250kias


#11

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