16 psi, it overcomes the spring and opens the cyclic valve. Wing  and  Empennage  Deice Timing Controller The timing controller is located in the left load center.  This  device  collects  logic  information necessary to provide control signals to the cyclic valves through solid-state sequence switching. The controller  provides  30-second  sequential  control signals to each cyclic valve. It also receives the 60°  temperature  sensor  indication  and  interrupts the  valve-open  cycle  when  aircraft  skin  and structural   temperatures   exceed   60°±3°F (15°±1.6°C). The timing controller collects logic signals  to  control  deice  operations  in  various failure modes. Probe Sensor Temperature Transmitter The   temperature   sensor   is   a   solid-state semiconductor thermistor whose resistance varies with  temperature.  There  are  eight  temperature sensors, positioned just inside wing and horizontal stabilizers  leading  edge  skins.  Each  is  located  to correspond to one of the eight deice piccolo tubes. When a leading edge skin temperature reaches 60°±  3°F,  an  electrical  signal,  furnished  by  a temperature   sensor   to   the   timing   control, interrupts the operating sequence of the related cyclic valve. Deice air to the particular piccolo tube sensed by that temperature sensor is shut off. Deice  Thermostatic  Switch The  thermostatic  switch  consists  of  a  con- ventional  bimetallic  element  that  closes  at  a temperature   of   200°±5°F   (93°±2°C).   Eight thermostatic  switches,  mounted  on  structural components  away  from  the  piccolo  tube  outlets, detect possible overheating of area structures. Any thermostatic switch closure causes the DEICE HOT  warning  indicator  light  on  the  annunciator panel to come on, but it does not disable a deice component. ENGINE ANTI-ICING SYSTEM A typical  aircraft  engine  anti-icing  system  is designed to allow hot 14th stage bleed air to be distributed to portions of the engine to prevent the formation of ice. The S-3 engine anti-icing system, shown in fig. 1-11, is controlled by a solenoid-operated anti- icing  valve  actuated  by  the  anti-icing  switch on  the  environmental  control  panel.  The anti-icing valve opens when electrical power is removed. A pressure switch, located on the anti- icing valve, senses pressure downstream from the valve, closes the circuit to the A-ICE ON light when the anti-icing switch is in ENG & PITOT (valve open), and opens when the switch is in OFF (valve  closed). When the anti-icing switch is positioned in ENG & PITOT, hot 14th stage compressor bleed air is ducted to the fan nose splitter and air inlet fairing via the engine nose pylon. The anti-icing valve regulates the output air pressure.  It  includes  a  backup  pressure  regulator in case of failure of the primary element. A pop- out button on the valve indicates primary pressure regulating   element   malfunction. Air from the anti-icing valve is directed to the anti-icing  discharge  manifold  where  it  is  split into two flows. One flow is for engine anti-icing, the other is directed to the engine air inlet anti- icing   connection. The engine anti-icing system consists of an anti-icing valve, anti-icing discharge manifold, anti-ice external air duct, and a forward anti-ice duct. Anti-Icing Valve The anti-icing valve is a solenoid-operated valve  actuated  by  the  three-position  anti-icing switch.  The  anti-icing  valve  is  de-energized open.  Failure  of  electrical  power  causes  the system to remain in or revert to the anti-icing ON condition. Anti-Icing  Discharge  Manifold The anti-icing discharge manifold is connected to  the  anti-icing  valve  and  provides  for  the distribution  of  the  hot  14th  stage  bleed  air to  the  air  inlet  fairing  and  to  portions  of  the engine. 1-17