slowing it down.

[EagleRJ]

One trick is to use multiples of 60- whichever is equal or greater to your groundspeed- and convert it to miles. Example:

You are 125 miles from the airport (1000 MSL) at FL280, with a groundspeed of 450 Kts.

Next highest multiple of 60 = 480 (60*8) = Eight miles a minute.

Assuming 1000 FPM decent rate, 27 minutes equates to starting your decent 216 miles out.
...or 108 miles out at 2000 FPM,
...or 72 miles out at 3000 FPM.

Keep in mind that there are a lot of variables that will impact any linear system like this- changing wind, intermediate ATC level-offs, and having to level at 10,000 to slow down. Like others have said, it's hard to decend clean in most jets, and you should treat below 10,000 and inside 30 miles as being "in the pattern".

Most modern jets have VNAV/FMS decent planning, which is the best thing since sliced bread!
Math = bad!

 

[FracCapt]

One trick is to use multiples of 60- whichever is equal or greater to your groundspeed- and convert it to miles. Example:

You are 125 miles from the airport (1000 MSL) at FL280, with a groundspeed of 450 Kts.

Next highest multiple of 60 = 480 (60*8) = Eight miles a minute.

Waaaaaaaaaay too much math dude! Altitude to lose times three...that's how far out you need to start down. Altitude to lose times four if you have a tailwind. That'll get you down in every jet I've flown. This assumes a flight idle descent. It will likely get you down well before you need to be....but that's better than blowing your crossing restriction. This formula does not work very well when doing 250KIAS. Most jets don't descend more than 2000fpm at 250KIAS when clean....though, you can increase that with speedbrakes(or thrust reverse on the #2 and #3 engines on a JT8 engined DC-8).

 

[jimpilot]

Gulfstream

Altitude X 3 = distance to start down has worked in G3 to GV