The S-3 aircraft ice protection system provides deicing of wing leading edge flaps and horizontal stabilizer leading edges and anti-icing of the air-conditioning ram air inlet, engine nacelle, and parts of the engine. The bleed air temperature control anticipator and thermostat, the deice temperature control regulator valve, and the engine anti-icing valve interface with the ice protection system. The deice function of the ice protection system removes ice that forms on the leading edges of the wing and horizontal stabilizer. The vertical. stabilizer leading edge is not deiced. Bleed air from the engine compressor's 10th stage is the basic source of heat. One requirement of the bleed-air supply subsystem, in addition to supplying deice air, is to control the temperature of that supply. The high-stage bleed-air regulator valve primarily maintains a set pressure schedule in the bleed-air manifold. During deice operations this function is expanded to maintain a temperature of 500 25 F (260 14 C) (or maximum 14th stage temperature, if less than 500 F).

Pneumatic signals from the bleed-air control temperature thermostat and anticipator are fed to the deice temperature control regulator valve (fig. 1-10), which, in turn, signals the high-stage bleed-air regulator valve to open, as necessary, to satisfy either the pressure schedule or the 500 F requirement, whichever needs the larger amount of 14th stage bleed air. Both engines are connected by the cross-bleed manifold, which provides a

flow path for bleed air from either one or both engines. The total deice system is controlled by the timing control, which uses pressure regulator valves and cyclic valves to direct bleed air in the proper sequence to each of the eight deice segments. Sequencing minimizes bleed-air con-sumption. Bleed air is ported from the cross-bleed manifold to each of the pressure regulator valves. The pressure regulator valves are energized by setting the DEICING switch on the environmental panel on the center console to WING EMP (wing and empennage). Setting this switch energizes a solenoid that ports pressure from the bleed-air supply to open the pressure regulator valve. Duct pressure is regulated by the pressure regulator valve to 26 2 psi. In the de-energized position, the pressure regulator valves are pneumatically

Figure 1-10.- Ice protection system.

and spring-actuated to the closed position and serve as system shutoff. With the pressure regulator valves in the energized position, bleed air flows through ducting to the cyclic valves. Any time the empennage pressure regulator valve is open, the ram air scoop ejector is provided with a continuous flow of bleed air for anti-icing. The cyclic valve solenoid, when energized, ports pressure to the inlet side of the cyclic valve, and vents the outlet side of its pilot valve to atmosphere. Pneumatic pressure from the inlet side causes the cyclic valve to open. Bleed air will then flow through the ducting for that segment to the respective piccolo tube, where it is directed to flow onto the inner skin surface to raise the skin temperature above freezing. On the wing, bleed air flows along the contour of the skin, and is vented overboard between the leading edge flap lower seal and the fixed wing. For the horizontal stabilizer, the bleed air, after leaving the piccolo tube, flows spanwise in the leading edge plenum, and flows overboard at the tips. To ensure that the flow of bleed air is directed to the appropriate points regardless of the positions of movable surfaces such as leading edge flaps and the horizontal stabilizer, extension ducts and leakproof rotary joints are incorporated. Also, a special wing fold seal permits wing folding while providing a leakproof junction when the wings are spread.

The timing control provides electrical signals to operate the pressure regulator valves and the cyclic valves in the proper sequence. The sequence is as follows: left outboard wing, right outboard wing, left center wing, right center wing, left inboard wing, right inboard wing, left horizontal stabilizer, and right horizontal stabilizer. Electric power (28 Vdc) is applied to the timing control by setting the deice switch on the environmental panel on the center console to WING EMP for continuous operations, or to SINGLE CYCLE for operation of the system, through one complete sequence. Setting the deice switch to WING EMP energizes the solenoids on the pressure regulator valves, which causes all three pressure regulator valves to open if a bleed-air pressure of 30 psi or more is available. This pressure allows bleed air to flow to the eight cyclic valves. If the wings are folded, the wing pressure regulator valves will not be energized because the wing fold interrupt switch will be in the open position. When the wings are extended, the timing control energizes the cyclic valves in proper sequence. Each solenoid is energized for 30 seconds, which causes each cyclic valve to be pneumatically opened by bleed air, to allow hot bleed air to flow through the piccolo tube for 30 seconds or until the skin reaches 60 3 F (15 1.6 C) as sensed by the temperature sensor. When the skin temperature exceeds 60 3 F, the temperature sensor provides a signal to the timing control to de-energize the solenoid for that cyclic valve. For in-flight operation, setting the deice switch to SINGLE CYCLE will cause the system to operate in the same way as it does when the deice switch is set to WING EMP except that upon completion of one sequence, the switch will return to the OFF position. For ground operation and checkout of the deice system, setting the deice switch to SINGLE CYCLE will permit the system to function through one complete cycle even if the skin temperatures exceed 60 3 F. The interrupt feature of the temperature sensors is disabled only in the single-cycle mode and only when the aircraft is on the landing gear. If a cyclic valve fails to fully open when scheduled, a mechanical position switch signals the timing control, which causes the DEICE FAIL indicator light on the annunciator panel on the center instrument panel to come on. This indicator light will go off when the 30-second interval for that cyclic valve is completed. If the pressure regulator valve fails in the closed position, bleed air will not be available to actuate the cyclic valve. Again, the DEICE FAIL indicator light will come on for each cyclic valve downstream from the malfunctioning pressure regulator valve.

If a temperature sensor fails or a cyclic valve fails while open, which results in the skin temperature exceeding 200 5 F (93 2 C), a thermo switch closes, and the DEICE HOT indicator light on the annunciator panel comes on. The WING EMP deicer system is functional during all normal flight operating conditions. During the engine-start cycle and during single-engine operations, the deice system is functionally inhibited. Normal deicing becomes available when both engines are operating. When operating on a single engine, deice can be recovered by setting the air-conditioning and deice switches on the environmental panel to OFF/ RESET and WING EMP, respectively.

Engine and engine nacelle inlet anti-icing (fig. 1-11) is accomplished by 14th stage bleed air, which is separated, in each engine pylon, from 14th stage air being used for other environmental control system (ECS) purposes. The anti-ice switch on the environmental panel on the center console, when set to the ENG & PITOT position, opens both engine anti-icing valves by de-energizing their solenoids to direct 14th stage bleed air, regulated to 22.5 2.5 psi, to the engine nacelle leading edges and engine anti-icing systems. The position of each anti-ice valve is shown on the copilot's advisory panel; 1 A-ICE ON and 2 A-ICE ON indicator lights come on whenever the anti-ice valves are open. The engine anti-ice switch also opens the empennage pressure regulator valve to provide a source of constant bleed air to the ram air inlet duct anti-icing shroud

(unless the deice system is being operated, the empennage cyclic valves will remain inactive/ closed). The engine anti-icing valve activates the entire deice system. The deice system cannot be operated until the anti-ice switch is set to the ENG & PITOT position.

The bleed-air deice/ anti-icing system consists of deice pressure regulating valves, bleed-air solenoid valves, a WING & EMP deice timing controller, a probe sensor temperature trans-mitter, and a deice thermostatic switch.