747飞机维护手册AMM CHAPTER 34 - NAVIGATION 第34章导航1(99)

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 3.  A/T-TAT/EPRL Mode Selector Panel (Fig. 1)
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 A.  The auto throttle-total air temperature/engine pressure ratio limit (A/T-TAT/EPRL) mode selector panel is an electromechanical with lighted push switches and rotary switches to select EPRL modes, auto throttle modes, alternate engine rating limits, decrease engine limits, and test modes. Also, on the panel is a decrease display to indicate the amount of decrease selected.
 B.  The EPRL mode rotary selector switch positions are takeoff dry (TOD), maximum continuous (CON) maximum climb (CLB), maximum cruise (CRZ) and go-around (GA). These modes select the maximum EPRL engine speed as computed by the TAT/EPRL computer. The switch is solenoid held and will return to GA mode whenever GA mode is armed by the A/P-F/D system or auto throttle system. The mode switch will return to GA mode with or without auto throttle engaged.
 C.  The rating selector pushbutton switches permits selection of alternate EPRL limit program in the TAT/EPRL computer. This permits programmed maximum engine speed reduction for different engine characteristics. The respective switch illuminates green when selected. A second push of the switch disengages the rating selection. Rating selection must be accomplished prior to auto throttle engagement when in takeoff mode.
 EFFECTIVITY

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 D.  The decrease switch permits selection of incremental reduction of EPR limit whether the auto throttle is engaged or not. A switch is used to select the desired decrease which is displayed on digital panel readouts Decrease increments are 0 EPR with a maximum selection of .06 EPR. The decrease is automatically reset to zero when a rating select is engaged. The decrease automatically resets to zero when auto throttle is engaged in any mode except TOD EPR; when a new auto throttle mode is selected with the auto throttle engaged or when auto throttle go-around mode is activated. After go-around arm, decrease may be selected and will not reset when go-around EPR mode is engaged.
 E.  The auto throttle mode pushbutton switches labeled EPR, MACH and SPEED are interlocked to permit selection of one mode only. The desired auto throttle mode must be selected before the auto throttle can be engaged. The respective mode switch illuminates green when the mode is selected. Mode selection is cancelled when the auto throttle is disengaged. When the airplane is on the ground and TOD is selected on the EPRL mode switch the mach and speed modes are inhibited allowing selection of EPR mode only (Ref 22-31-00 for the Auto Throttle System).
 4.  TAT/EPRL Indicator (Fig. 1)
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 A.  The TAT/EPRL indicator is a dc motor-driven, electromechanical indicator which is not hermetically sealed. The indicator displays total air temperature from -60 to +60.C, engine pressure ratio limit from 1.000 to
 1.995 and mode of operation.
 B.  The TAT and EPRL displays consist of rotating counters which are driven by permanent magnet type dc motors. The mode of operation is displayed on an eight position drum, actuated by a rotary solenoid-potentiometer combination. Meter movements are used to provide failure indications and to indicate whether the TAT readout is positive or negative. Warning flags drop over the TAT and/or EPRL displays when a failure is detected by the computer or indicator.
 C.  A self-contained power supply in the indicator allows the TAT portion of the indicator to operate independently of the computer. Without a computer installed, the indicator can still be used as a valid TAT indicator.
 5.  Operation (Fig. 2)
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 A.  Functional Description, TAT/EPRL System
 (1)  General
 (a)  
The A/T-TAT/EPRL mode selector panel controls the TAT/EPRL system and the A/T system in terms of basic A/T selection and precise EPR control in the EPR mode for the varying conditions under which the engines are required to operate; e.g., takeoff, climb, cruise, go-around. Different engine EPR limits and auto throttle operating mode, alternate engine ratings and decrease limits plus a test mode are provided on the panel.

 (b)  
A detent held solenoid reset rotary switch is provided on the mode selector panel for selection of the TAT/EPRL modes. The output of the switch is a voltage ratio derived from the TAT/EPRL computer voltage references. The TAT/EPRL modes that can be selected are takeoff dry (TOD), continuous (CON), climb (CLB), cruise (CRZ), and go-around (GA).

 EFFECTIVITY

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V95 VALVE-PACK 3
V94 VALVE-PACK 2 FLOW CONT & SD
FLOW CONT & SD (STA 1121, WL 91, RBL 50) (STA 1231, WL 109, LBL 70)
　
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