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MAINTENANCE MANUAL
C. The left side AOA sensor resolvers No. 1 and No. 2 provide angle of attack information to the left ADC. The right side AOA sensor resolvers No. 1 and No. 2 provide angle of attack information to the right ADC. Resolvers No. 1 from the left AOA and No. 2 from the right AOA provide angle of attack information to the center ADC.
D. The appropriate AOA sensor is selected by switching the ADC source destination identifier (SDI). An SDI of 1 selects the left AOA sensor. An SDI of 2 selects the right AOA sensor. The SDI input discretes to the center ADC are switched by the first officer's source select relay.
E. The AOA sensor has a solid-state vane heater which provides anti-icing for the sensor vane (Ref 30-31-00).
4. Total Air Temperature (TAT) Probe
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A. The total air temperature probe is a small metal strut mounted on the airplane skin. It senses the temperature of airflow passing through cavities within the strut. The probe contains a sensing element and an anti-icing heater. The sensing element consists of two temperature sensitive elements whose resistance changes as a function of the air temperature around them. At 0° C the resistance of the sensing elements is approximately 500 ohms. In flight, air passes through the probe and flows over the sensing element. During ground operation, bleed air from the pneumatic system (Ref 36-00-00) is supplied to the probe and causes air to be drawn through the probe and over the sensing element.
B. Two TAT probes are installed on the airplane fuselage just forward of the pilots' windshield. The left TAT probe provides air temperature data, as a resistance value, to the left ADC. The right TAT probe provides air temperature data, as a resistance value, to the right ADC.
C. The right TAT probe provides air temperature data to the center ADC.
D. The heating element provides anti-icing for the probe (Ref 30-31-00).
5. Air Data Source Select Switch
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A. The air data source select switch is a three position switch used to select the ADC in use by the active electronic interface unit (EIU).
B. There are no interlocks to prevent simultaneous selection by each pilot of the left and right ADCs. An interlock prevents the center ADC from being selected by both pilots at the same time. The IDS will provide an advisory message when data for the captain and first officer are both from the left or right ADC.
C. The air data source select switch is part of the captain's and first officer's source select module. The modules are located on the captain's P1-1 and first officer's P3-1 forward instrument panels.
6. Source Select Relay
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A. The source select relays switch the center ADC outputs for the left ADC or the right ADC when the captain's or first officer's air data source select switch is set to the C position. Both the captain and first officers source select relays are interlocked so that both cannot be at the center position at the same time.
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MAINTENANCE MANUAL
B. The captain's ADC source select relay (R7384) and the first officer's ADC source select relay (R7385) are located on the aft side of the station 420 floor beam above the electronics equipment racks in the main equipment center. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：747-400 AMM 飞机维护手册 导航 NAVIGATION 1(84)
