When to descend

Hi guys how many miles away from my airport should I start descending and roughly to what altitude should I be at

There are a couple easy ways to determine when to start your descent.

  1. Multiply your altitude by the number of thousands of feet by 3.
    Example: You’re cruising at 25,000ft, so 25 x 3 = 75, so will want to start your descent 75nm from the airport.

2.Start descent when the time to the airport equals altitude to lose for 1000 ft/min descent.
Example: 10,000 feet to lose, start descent 10 minutes out at 1000 ft/MIN.

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Okay thanks for the help both of you I’ve worked when to descend now thank you very much

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Okay thank you for youre help I’ve worked out when I need to descend

For number one, what should your VS be then? -1000?

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Usually I descend at no more than -1000VS, so if I have 11 minutes until the airport, and i’m at 11,000ft I’ll need to set VS to -1000VS. If it gets tricky use a calculator :-)

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http://www.freedomair.us/DescentCalc/descentdistance.php

@jooeball

How to calculate rate of descent.

Method 1 - Ground speed x 5. 3 will give you your required rate of decent for a 3 degree glide slope.
Example: GS 300kts, 300 x 5.3 = 1590. Since VS adjusts in increments of 100, you should round off to VS -1600. It is better to come in early and level off than coming in high and having to dive bomb the airport.

Method 2 - Some people multiple Ground Speed by 6,
Example: GS 300 x 6 = -1800. Again better to come down early and level off to your next waypoint or to the start of the glide slope. Some multiply by 5, but I always seem to come in high using 5.

Method 3 - Divide your ground speed by 2 and add a zero.
Example - Ground speed 300kts ÷2=150, add the zero for VS of - 1500

Method 4 - Start descent when the time to the airport equals altitude to lose for 1000 ft/min descent.
Example: 10,000 feet to lose, start descent 10 minutes out at 1000 ft/min.When you reach the ILS follow the ILS glide slope, using method one.


Method 1 is the most accurate, but you need to keep adjusting the VS as the ground speed decreases. Perfect for final approach.

Methods 2 is good for descending from 10,000 to 3,000.

Method 3 is very easy and gets you close to where you want to be.

Method 4 is useful when descending between waypoints when above 10,000 feet. I also use it between waypoints down to 3,000 feet above ground level.

All these methods require regular adjustments as your speed and time change.

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