Originally Posted by
Propellerhead
The problem comes when you’re given a speed and a “decend to xxxx by xxx”. It can do the path or it can do the speed. If you want both you have to work at it. As someone said - moving the thrust levers manually / using the speed brake is one option.
I think that’s the crux of the matter. If you have an ATC speed constraint it is likely for separation/sequencing so really should be adhered to - it may need thrust or drag but not both to make a target altitude.
Sometimes it’s just not possible to do a whole descent in VNAV PTH without intervention if there are rapid changes in wind velocity on the way down. Often, you’re just above or in a jet core so attempting to fly a fixed angle in the descent leads to under/over speed in fairly short order.