8. LEARNING STEP/ACTIVITY No. 8. Identify the operational characteristics of the engine anti-ice system.
a. Engine Anti-Ice System Overview- The engine anti-ice system is comprised of two separate systems, the engine anti-ice and engine inlet anti-ice. Both prevent ice from damaging the engine and are activated by one switch. The engine A/I is controlled, or actuated, through the AISBV. The engine inlet A/I is controlled, or actuated, through the inlet A/I valve and the ambient air sensor. Each system has it's own advisory light located on the caution/advisory panel. When the engine and engine inlet A/I is activated, a 16% loss of MTA for that engine is realized; with the cabin heat on an additional 4% reduction of MTA occurs for a total of 20%. This is based on the assumption that both systems are active. Electrical power is required to deactivate both systems, if there is the absence of electrical power; the system has a fail-safe causing the A/I system to be active.
Anti-Ice Airflow- The Engine A/I is pilot activated electrically through the engine anti-ice switch on the upper console. When the switch is placed in the "ON" position, electrical power is removed from a solenoid in the AISBV. The AISBV sequences open to direct hot fifth stage compressed air, P-2.5, through ducting that anti-ices each swirl vane, the nose splitter, and each IGV. A micro switch within the AISBV illuminates the ENG ANTI-ICE ON advisory light. Keep in mind, the AISBV is also actuated mechanically by the HMU for compressor bleed functions; this also causes illumination of the ENG ANTI-ICE ON advisory light.
b. Engine Anti-Ice- The Engine Inlet A/I is also pilot activated via the engine anti-ice switch on the upper console. When the switch is "ON" the engine inlet A/I is "ARMED", meaning it may or may not activate. Activation of engine inlet A/I depends on ambient temperatures detected at the ambient air sensor in the inlet, preventing activation of inlet A/I in hot environments, possibly causing damage to the fiberglass inlet assembly. The inlet A/I valve is connected to it's own P-2.5 supply, allowing it to function independent of engine A/I. When active, stage 5 air (P-2.5) is directed through fiberglass ducting and out the gill slits of the engine inlet assy.
Engine Inlet Anti-Ice Airflow- The ENG INLET ANTI-ICE ON light is illuminated via a thermal switch inside the inlet when the inlet temperature reaches 93°C. At ambient air temperatures between 4-13 oC the valve may be open or closed. At 4 oC or colder the valve must be open, at 13 oC or warmer the valve must be closed. This prevents overheating of the fiberglass inlet assembly.
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Engine Anti-Ice Activation- At ambient temperatures of 4o C and colder, when the NO. 1 or NO. 2 ENG ANTI-ICE switch is placed in the ON position, the corresponding ENG ANTI ICE ON advisory light will illuminate. Activation of the corresponding ENG INLET ANTI ICE ON advisory light indicates that inlet anti-icing is being provided and the fairing temperature is at 93o C.
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