Is there a proper way to calculate when to slow down and start the descent?

From FlightSim

Q:

IS THERE A PROPER WAY TO CALCULATE WHEN TO SLOW DOWN AND START THE DESCENT?

A:

As to a guide for the descent point, two methods could be:

a) your altitude divided by your average rate of descent will give you the time in descent in minutes. Just multiply that by your average ground speed. That will be the approximate distance required.

Say in big jets, from 33000ft at 2500fpm average you will need approxy 12 minutes and at average 8nm a minute ground speed it would be 13X8 =104nm. It will put you overhead at same speed!!!!! So, add 7 to 8 miles as you need for the deceleration/approach segment etc. and commence descent at 121 nm. You also correct for wind by taking off/adding approxy 15% of your Head/Tail Wind component.

OR

b) You lose 300ft per each nm dist in a 3 deg glide slope. So from 33000 ft, you descend at 33000/300= 110nm. Add 7 miles for deceleration and descend at 117 nm.

For Wind!!!!! Well! If your a/c has a ground speed read out no need for correction at all as long as you maintain a 3 deg glideslope. How to do that? Keep your rate of descent at all times equal to half your GS X 10, ie ROD = Half ground speed X 10. For e.g. if your GS is 300kt your ROD should be 1500 fpm. etc. You need to keep adjusting power to do this and the wind is automatically taken care of.

through out the descent you can keep cross checking :- Leaving 7 miles for deceleration,

At 107 miles you should be at  100 x 300 = 30000 ft
    97                     at              27000 ft
    87                     at              24000 ft
    77                     at              21000 ft

..........Notice 3000 ft for each 10 miles........

    47                     at              12000 ft at 300kt

..........If you decelerate now to 250 kts......

from now on leaving out the 7nm

    40 miles  .............................12000 ftat 250kt
    30        ............................. 9000 ft
    20        ..............................6000 ft
    10        ..............................3000 ft

Any time you decelerate and take your flaps, gears etc all that needs to be done is to keep that rate of descent half of your ground speed x 10.

In case if you happen to be high or low then increase or decrease your ROD to be more than /less than the half ground speed figure till you catch up with your 3 deg slope and then start maintaining base ROD.

In a nut shell, simple facts. 300 ft for each mile. Add 7nm or what you are comfortable with. Half the number on your GS indicator as your ROD.

bala