If the pilot sets an RPM on any jet engine the function of the fuel control unit is to maintain that RPM regardless of any change in airspeed or altitude UNLESS changes are needed to keep the engine inside any of its operating limits.
So even if I set the RPM (N1 setting) using the throttle levers only and not any FMC or any computer, any fuel control unit will still maintain the N1? Are you sure this applies even in small jets etc.?