14 CFR 23.1141 - Powerplant controls: General.
(b) Each flexible control must be shown to be suitable for the particular application.
(c) Each control must be able to maintain any necessary position without -
(1) Constant attention by flight crew members; or
(2) Tendency to creep due to control loads or vibration.
(d) Each control must be able to withstand operating loads without failure or excessive deflection.
(e) For turbine engine powered airplanes, no single failure or malfunction, or probable combination thereof, in any powerplant control system may cause the failure of any powerplant function necessary for safety.
(f) The portion of each powerplant control located in the engine compartment that is required to be operated in the event of fire must be at least fire resistant.
(g) Powerplant valve controls located in the cockpit must have -
(1) For manual valves, positive stops or in the case of fuel valves suitable index provisions, in the open and closed position; and
(2) For power-assisted valves, a means to indicate to the flight crew when the valve -
(i) Is in the fully open or fully closed position; or
(ii) Is moving between the fully open and fully closed position.