So rn I’m flying from JFK to CDG with an Air France 777-200ER… I’m at an altitude of Lvl420 so autopilot is using Mach, however, I guess Mach system isn’t really working, cuz the limit (in rules) of speed, is Mach 90… still I have .95 Mach set in AP but it doesn’t really warms me or anything… Also, when adding speed to AP, the plane doesn’t respond and stays at same speed… so…
I don’t really understand the full problem, but from I can gather your aircraft should not be flying at M.90 it should be flying at speeds such as M.83- M.86
In addition to what @DeerCrusher said, even if you have your AP set to M .95, it doesn’t mean you can reach that speed due to performance of the aircraft, weight and so on.