14 C.F.R. § 29.1147 – Mixture controls.

(a) If there are mixture controls, each engine must have a separate control, and the controls must be arranged to allow—
1. (1) Separate control of each engine; and
2. (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.