How far away from the runway should I start my descent?

Question

How far away from the runway should I start my descent?

Answer 1

If you are flying in a controlled airspace, your descent is not a question of how far but when it is safe subject to an ATC clearance. The CONTROLLER decides when you are cleared to descend in order to maintain safe, orderly and expeditious flow of air traffic.

Answer 2

A popular rule of thumb for this is to do a 3 to 1 descent profile.  Here's what you do:

How far out should I start my descent?:  Take your altitude that you need to loose and divide by 300.  That will tell you how many miles out you should start your descent.  For example, if you're at 30,000 feet and need to land at an airport that is at sea level, you should start your descent about 100 miles out.

What descent rate should I use?:  Take your ground speed, add a 0 and divide by 2.  That will tell you how many feet per minute you should maintain.  Multiplying your ground speed by 5 will result in the same answer, but I find it easier to add a 0 and divide by 2.

Now, military fighter guys might do things differently, but these are useful for anything from small single-engine GA planes up to the big jets.

Answer 3

Rob G. has an excellent "rule-of-thumb" answer that is commonly used by commercial pilots, but he left out some important points. If you are flying an unpressurized aircraft, descents greater than 1000 feet per minute are very uncomfortable for the passengers and 500 fpm is a more standard descent rate. In pressurized aircraft, 1,000 to 2,000 fpm is a typical descent rate (although in a pinch you can do 3,000-4,000 fpm or more).

Based on "standard" descent rates, divide the total number of feet you have to descend from cruising altitude to the airport by the descent rate, which gives you minutes. Multiply that by your groundspeed in miles-per-minute and you'll have your answer.  

Example 1: You're flying an unpressurized airplane such as a Cessna 182 at 8,000 feet and the airport is at 1,000 feet. Divide 7,000 feet  by 500 fpm, which is 14 minutes. If you're going 120 knots (2 miles per minute), the distance is 28 miles.

Example 2: You're in a pressurized aircraft like a King Air at 30,000 feet and have to descent to 2,000 feet. 28,000 feet divided by 1,500 fpm is 21 minutes. At 300 knots (5 miles per minute) that is 105 miles. At a 2,000 fpm descent rate, the distance is 70 miles.

Also pay attention to the height of intervening terrain or obstacles which might encroach upon your descent path and adjust your rate of descent and / or your speed accordingly so that you can safely clear it. You may need to calculate one rate of descent to clear the obstacle, and another from there to the airport.

Answer 4

I hope that you are not actually airborne while you are waiting for the answer to this question !!!.

Answer 5

That depends on the type of plane you are flying.

Good Luck...