I’ve noticed several posts discussing the problem of disengaging auto throttle on the Cessna Citation Longitude during approach phase. AT always works great during Departure and Arrival phases. However, I typically try to take over manual control of the throttle at about the faf waypoint of the approach phase by hitting the AT toggle button (I have tried with SPD in both FMS and MAN) - often without success. Manual movement of the aircraft throttle is totally ineffective in changing aircraft speed despite the panel indicating decreasing power when I move decrease the aircraft throttle. Any ideas on what I am doing wrong or how I can correct this? Some suggestions are to toggle AP on an off but this doesn’t seem to work? Anybody else encountered this problem or found a solution. Any pointers welcomed.