Sources of Operating Air Turbine Engine Bleed Air Pneumatic Deice Boot System for GA Aircraft GA System Operation 15-13 Combining functional components of a deice system into  a single unit is fairly common.  Figure 15-20  illustrates the  right side of a large aircraft deice boot system. The left side  is the same. In addition to the distributor valves, which  combine functions of a control valve and deflate valve, the  Figure 15-18  shows a deice system used on a GA twin-engine  aircraft with reciprocating engines. In normal flight, all of the  components in the deice system are de-energized. Discharge  air from the dry air pumps is dumped overboard through the  deice control valves. The deflate valve is open connecting the  deice boots to the suction side of the pump through the check  valve manifold and the vacuum regulator. The gyroscopic  instruments are also connected to the vacuum side of the dry  air pump. The vacuum regulator is set to supply the optimum  suction for the gyros, which is sufficient to hold the boots  tightly against the airfoil surfaces.  On this simple system, the pilot must manually start this  inflation/deflation cycle by pushing the switch each time  deice is required. Larger aircraft with more complex  systems may include a timer, which will cycle the system  automatically until turned OFF. The use of distributor  valves is also common. A distributor valve is a multi- position control valve controlled by the timer. It routes  air to different deice boots in a sequence that minimizes  aerodynamic disturbances as the ice breaks of the aircraft.  Boots are inflated symmetrically on each side of the fuselage  to maintain control in flight while deicing occurs. Distributor  valves are solenoid operated and incorporate the deflate valve  function to reconnect the deice boots with the vacuum side  of the pump after all have been inflated. When the switch shown in  Figure 15-19  is pushed ON, the  solenoid-operated deice control valves in each nacelle open  and the deflate valve energizes and closes. Pressurized air  from the discharge side of the pumps is routed through the  control valves to the deice boot. When the system reaches 17  psi, pressure switches located on the deflate valve de-energize  the deice control valve solenoids. The valves close and route  pump air output overboard. The deflate valve opens and the  boots are again connected to vacuum. GA aircraft, especially twin-engine models, are commonly  equipped with pneumatic deicer systems. Rubber boots are  attached with glue to the leading edges of the wings and  stabilizers. These boots have a series of inflatable tubes.  During operation, the tubes are inflated and deflated in an  alternating cycle.  [Figure 15-17]  This inflation and deflation  causes the ice to crack and break off. The ice is then carried  away by the airstream. Boots used in GA aircraft typically  inflate and deflate along the length of the wing. In larger  turbo prop aircraft, the boots are installed in sections along  the wing with the different sections operating alternately  and symmetrically about the fuselage. This is done so that  any disturbance to airflow caused by an inflated tube is kept  to a minimum by inflating only short sections on each wing  at a time.  The source of deice boot operating air on turbine engine  aircraft is typically bleed air from the engine compressor(s).  A relatively low volume of air on an intermittent basis is  required to operate the boots. This has little effect on engine  power enabling use of bleed air instead of adding a separate  engine-driven air pump. Valves controlled by switches in the  cockpit deliver air to the boots when requested. The source of operating air for deice boot systems varies with  the type of powerplant installed on the aircraft. Reciprocating  engine aircraft typically use a dedicated engine-driven air  pump mounted on the accessory drive gear box of the engine.  The suction side of the pump is used to operate the gyroscopic  instruments installed on the aircraft. It is also used to hold the  deice boots tight to the aircraft when they are not inflated.  The pressure side of the pump supplies air to inflate the deice  boots, which breaks up ice that has formed on the wing and  stabilizer leading edges. The pump operates continuously.  Valves, regulators, and switches in the cockpit are used to  control the flow of source air to the system. Figure 15-17.  Cross-section of a pneumatic deicing boot uninflated  (top) and inflated (bottom).