misctw

I just did my first flight (with several years' experience with the Fenix A320). I encountered two problems: 1. At an altitude restriction (15000ft) during climb, the A350 accelerated until it oversped. 2. I pushed the altitude button at the top of the descent after I had set a lower altitude. I saw the button being pushed in, and the PFD changed accordingly, but the plane did not start the descend! It remained stuck at the cruise altitude. The same thing happened when I "pulled" the button. The PFD changed to "open" descend, but the plane remained at cruise altitude. Does anybody have an idea? Thank you! Michael