Top Of Descend: When Do You Start Your Descent? - [Calculations and Tips from an Airline Captain]

In today’s video, we are going to talk about the TOP OF DESCEND.

The Top of Descend is the point at which you have to start your descend into your destination Airport.

If you are flying in a small Single Engine Pistons at 1000 feet it is not difficult to calculate your TOD, you just look outside and when your airport is close enough you start the descend by simply looking at the runway.

However, if you are flying a Jet cruising at 30000 feet then it gets a bit more difficult to start your descend by looking at the runway.

So you need a way to calculate your Top of Descend in order not to end up too high and miss the runway.

Let's imagine you are cruising at 30000 ft with a speed of 280 knots and with a Tailwind of 30 knots, our goal is to know how many Nautical Miles you need in order to descend, decelerate (taking into account the wind), get established on final and land into your destination that is a 0 elevation.

First, take the first 2 digits of your cruising altitude and multiply it by 3, so 30 multiply by 3 is 90, these are the nautical miles to lose the altitude.
Second, take your speed and for every 10 knots above 200 knots add one mile of your top of descend. So, 80 knots equal to 8 Nautical Miles.
Third, Add 1 Nautical Mile for every 10 kt of tailwind, in this case, 30 knots of tailwind so 3 Nautical Miles.

If you some up all these three calculations you will come up with your Top of descend, 90+8+3 equal 101 Nautical Miles.

So, if you are cruising at 30000 feet at 280 knots with 30 knots of tailwind you need to start your descend 101 nautical miles before the runway.

If you want to know how the aircraft calculates the descend watch the following Video:
   • VNAV: What is it and why is it import...  

If you want to know the difference between Altitude and Flight Level watch the following:
   • QNH, QFE and QNE -  [Altitude, Height...  

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Disclaimer:
THIS VIDEO IS FOR ENTERTAINMENT PURPOSES ONLY.
NOT FOR REAL-LIFE OPERATIONS.
PLEASE REFER TO THE OFFICIAL MANUAL AND DOCUMENTATION.
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