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.

Anti-Ice External Air Duct The anti-ice external air duct is connected to the inlet of the anti-icing valve and to the 14th stage of the engine to provide hot 14th stage bleed air to the anti-icing system.

Forward Anti-Ice Duct The forward anti-ice duct is connected to the engine nose pylon and the air inlet fairing anti-ice duct to provide hot 14th stage bleed air to the air inlet fairing.