AVIATION MENTAL MATH

[CPS1]

I like simplifying flying problems and hate excess paper in the cockpit.
What's your favorite mental math formula ?

[Yoyoma]

You know I hate posting things twice...So go see my formula in the Holds & Timing thread...

Yep..Go Flames Go

[oldtimer]

What works the best for me is to look at the right seater and say "What is your opinion?" Works for me.

[ahramin]

Yeah right oldtimer. First you steal this leg from me, now you want me to figure out the hold for you?

Thieves, you captains are all thieves. No sense of shame.

[CPS1]

Descent planning,
for a 500 FPM descent at 150 kts (ground speed).
If you want to be at 1000 agl by 3 nm from the airport and you have 4000 feet to descend, double the altitude you need to get rid of, in this case 4000 becomes 8000 and get rid of the zeros. You end up with 8.
It will take you 8 minutes for the descent. Multiply 8 by the number of miles per minute you are travelling 2.5 and voila, you have your answer :
you have to start your descent 8 minutes back or 23 nm from the airport.

[ahramin]

you have 4000 feet to descend, double the altitude you need to get rid of, in this case 4000 becomes 8000 and get rid of the zeros. You end up with 8

Or alternately, for those of you who do not view math as esoteric witchcraftry, just divide the altitude to be lost by the rate of descent.

4000 feet / 500 feet/minute = 8 minutes.

[dont_snag_it]

[oldtimer]

Why not just look at the DME and start down 10 minutes back for low altitude unpressurized and mid altitude pressurized, 15 minutes back from very high altitude. In the Lear, 460kts= 8 miles a minute, 45000 ft to 3000 ft = 42000 ft @ 3000 fpm = 12 min. add 3 min for slowdown @ 14000 and 10000. Now, with GPS it is even easier. 10 or 15 back from the IF. With a pressurized airplane, use a 500 fpm rate of descent on the cabin and adjust you timing to that. you will find most pilots will be @ 5000 ft above landing field altitude for most flights. Actual altitude for airplane, cabin altitude for pressurized.