Outer bearing assembly Counterweight assembly Inner bearing assembly Deicing slip ring Crosshead Backplate Flange attachment Operating pin assembly Hub Hub assembly bolts Cylinder Piston Blade assembly Blade grease seal Beta tubes Figure 7-47.  Turboprop propeller.  and propeller electronic control. Modern turboprop engines  use dual Full Authority Digital Engine Control (FADEC) to  control both engine and propeller. The spinner assembly is a  cone-shaped configuration that mounts on the propeller and  encloses the dome and barrel to reduce drag. The synchrophasing system is designed to maintain a preset  angular relationship between the designated master propeller  and the slave propellers. Propeller operation is controlled  by a mechanical linkage from the cockpit-mounted power  lever and the emergency engine shutdown handle (if the  aircraft is provided with one) to the coordinator, which, in  turn, is linked to the propeller control input lever. Newer  designs use electronic throttle control that is linked to the  FADEC controller. Turbo-propeller control assemblies have a feathering system  that feather the propeller when the engine is shut down in  flight. The propeller can also be unfeathered during flight, if  the engine needs to be started again. Propeller control systems  for large turboprop engines differ from smaller engines  because they are dual acting, which means that hydraulic  pressure is used to increase and decrease propeller blade  angle.  [Figure 7-48] The PT6 Hartzell propeller system incorporates three-, four-,  or six-bladed propellers made of aluminum or composite  materials. It is a constant-speed, feathering, reversing  propeller system using a single-acting governor. Oil from  the propeller governor feeds into the propeller shaft and to  the servo piston via the oil transfer sleeve mounted on the  propeller shaft.  [Figure 7-49]  As oil pressure increases,  the servo piston is pushed forward, and the feather spring  is compressed. Servo piston movement is transmitted to  the propeller blade collars via a system of levers. When oil  pressure is decreased, the return spring and counterweights  force the oil out of the servo piston and change the blade pitch  to a high pitch position. An increase in oil pressure drives  the blades towards low pitch. Engine oil is supplied to the governor from the engine oil  supply. A gear pump, mounted at the base of the governor,  increases the flow of oil going to the constant speed unit  (CSU) relief valve. When the oil pressure reaches the desired  level, the relief valve opens to maintain the governor oil  pressure. When the speed selected by the pilot is reached,  Pratt and Whitney PT6 Hartzell Propeller  System 7-32