Originally Posted by ShyGuy

I was on the Bus for years but now on Fifi and already forgot. Can someone remind me, the logic of managed descent when pulling speed knob to maintain a new ATC airspeed. Say you had 280 kts set in the descent page and pushed to start a managed descent. I remember it would bracket +/- 20 knots, so bars at 260 kts and 300 kts. If it was getting high on profile, it would pitch down more up to 300 kts and try to stay on profile. Idle power.

Lets say it's doing 280 kts perfect in the managed descent. ATC says slow to 260 kts for descent. You pull speed to 260, it changes from magenta to blue. That much I remember. Plane will initially pitch up to get 260 knots, then come down. But I forget, what's the logic now? Will the plane keep coming down at 260 kts at idle, including going below Vnav deviation dot (magenta)? Or will it add some power once it gets back on the Vnav deviation dot and maintain the 260 knots and stay on Vnav dot?