14 CFR § 29.1141

Powerplant controls must be located and arranged under § 29.777 and marked under § 29.1555.

Each control must be located so that it cannot be inadvertently operated by persons entering, leaving, or moving normally in the cockpit.

Each flexible powerplant control must be approved.

Each control must be able to maintain any set position without—

Constant attention; or

Tendency to creep due to control loads or vibration.

Each control must be able to withstand operating loads without excessive deflection.

Controls of powerplant valves required for safety must have—

For manual valves, positive stops or in the case of fuel valves suitable index provisions, in the open and closed position; and

For power-assisted valves, a means to indicate to the flight crew when the valve—

Is in the fully open or fully closed position; or

Is moving between the fully open and fully closed position.