If this is a duplicate please just delete it.
In this example we descent from FL180 to below 10000’.
This is just one example, there are many ways to do it, but this just shows you how to make it in a smooth way. You have to work with your Speed, Vertical Speed and the Speed Brakes ( Spoilers ).
Always watch how your Aircraft is executing a command, in general, when you are flying level and start a descent while maintaining a selected SPD ( using Autothrottle ) your Aircraft will:
- Reduce N1 as much as needed to not accelerate. Once the engines reached idle,
the maximum the Autothrottle System can help you with losing SPD is reached.
If you are still accelerating, it is now on you to assist. There are a few possibilities:
Use the Spoilers. In modern Aircraft with a supercritical wing profile like the B777 or planes with a
high aspect ratio wing design like the B787 it is nearly impossible to descent from Cruising ALT without use of the Spoilers/SPD Brakes, especially when ATC tells you: " Descent ALT/FLXXX , 2500 feet or more" ( This command does not excist in IF ), but when you are close to an Airport and too high the same situation can occure, you need to descent with a higher VS.
Work with your VS Reducing the VS will raise the nose of your aircraft and help you to reduce SPD
Set your selected SPD to a value below 250 kts. If you leave it at 250kts the autothrottle system will increase N1 when it reaches 250kts because it will assure just one thing: That you will not reach a SPD lower then what you selected. As the Autothrottle System is programmed like this it is very likely that it will use as much N1 OR MORE as needed to not become too slow. That can easily lead to a SPD greater then 250kts for a few seconds. Too long to not receive an overspeed warning in IF.
Just look the actions in the Video and the combination of using VS, Spoiler, SPD .
And as many said before : Stop your descent before you reached 10000’ and make sure you have a speed somewhere close but below 250 kts. That is one reason your friendly ATC Controller clears you most of the time first to 11000’ before instructing you " descent 9000’ ". To give you the time to prepare your aircraft for a further descent without overspeeding.
Hope this helps a little bit…