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## Calculating the distance when to start descending.

• Spinrecovery
• Topic Author

### Spinrecovery created the topic: Calculating the distance when to start descending.

Please correct me if i am wrong.
Lets say I am flying a cessna 172 doing 90 knots and I am on and outbound from station at 46 DME and I want to descend at 500 fpm from 5500 to 2500 which is 6 minutes.
So I use this formula: 90 knots * 6 minutes = 540, divide 540 by 60 9 NM. So I start start descending when I am 37 DME outbound.
Are there any quicker, easier, or ball park figures I can use to mentally finding out the distance I need to start descending?
Just curiosity, is it possible to use 1 in 60 rule to do this?
Cheers

• Spinrecovery
• Topic Author

### Spinrecovery replied the topic: Calculating the distance when to start descending.

can I use this method?
groundspeed is 120 knots which is 2 NM a minute and I want to lose 5000 of altitude at 500 FPM which it will take 10 minutes, so take 2 *10 = 20 NM
I should start descending 20 NM before reaching my destination.

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