FAA Federal Aviation Regulations (FARS, 14 CFR)

(a) If there are mixture controls, each engine must have a separate control. The controls must be grouped and arranged to allow --

(1) Separate control of each engine; and

(2) Simultaneous control of all engines.

(b) Each intermediate position of the mixture controls that corresponds to a normal operating setting must be identifiable by feel and sight.

(c) The mixture controls must be accessible to both pilots. However, if there is a separate flight engineer station with a control panel, the controls need be accessible only to the flight engineer.