(3)
The ENGINE RATING keys are used to make and indicate rating selections. There are three possible selections and only two keys. An alternate rating is selected at the limit select panel by pressing the related key so that it lights green. A full rating is obtained by depressing any lighted key so that neither key is lighted.
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(4)
Depressing a LIMIT MODE key commands the computer unit to select the related flight limit mode. The computer unit then resets previous selections and acknowledges the receipt of the command from the limit select panel. The key legend, backlighted blue for night use, then is underlined by a white bar to indicate the current limit mode selection of the computer unit.
(5)
The TEST switch is used to command a limit select panel lamp test. Depressing other keys while the TEST is also depressed enables testing of the individual keys.
8. Limit Indicator (Fig. 8)
_______________
A. The limit indicator contains a power supply, logic circuits, and displays. The limit indicator receives serial digital data from the computer unit which is converted into illuminated displays.
B. The four display lines are composed of 5 by 7 LED dot matrices which are lighted to form display characters. The characters include letters, numbers, mathematical symbols, and punctuation marks. Testing of the limit indicator is accomplished at the control display unit.
C. Limit Indicator Displays.
(1)
The top display line shows TAT (total air temperature in degrees centigrade) as calculated by the computer unit.
(2)
The second display line (RTG) shows the engine rating as selected through the limit select panel or through the control display unit.
(3)
On IB Airplanes, the third display line (LIM) shows the current basic (without derating) engine limit (engine pressure ratio limit). This limit is calculated by the computer unit using flight limit mode and engine rating selections, engine type and load data, as well as TAT and pressure altitude.
(4)
On AF Airplanes, the third display line (LIM) shows the current basic (without derating) engine limit (engine N1 percent RPM limit). This limit is calculated by the computer unit using flight limit mode and engine rating selections, engine type and load data, as well as TAT and pressure altitude.
(5)
The fourth display line (MODE) shows the flight limit mode as selected through the limit select panel or as selected through the control display unit.
9. Computer Unit (Fig. 1)
_____________
A. The computer unit (CU) continuously performs many computations at a high rate of speed. The primary function of the CU is to compute throttle power settings and pitch commands (vertical steering) using data from other PMS units and from other airplane systems along with stored performance, propulsion, and limitation data. The CU also checks reasonableness of inputs and outputs as well as its own operation. The CU consists of an ac-dc power supply, a ac-dc converter, a magnetic memory module, and 13 plug-in circuit cards. One of the circuit cards is a solid state read only memory. The remaining circuit cards make up a central processor and a program controlled input/output. The front panel has a ac-dc power supply as a protrusion, a handle that folds down when the CU is installed and two tangs for thumb screw mounting of the unit in the airplane.
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DISPLAY
SWITCHES
MANUAL KEY
(WHITE)
KEYBOARD
FORWARD/BACK
SLEW SWITCH
PMS ANNUNCIATOR (AMBER)
INS ANNUNCIATOR
INS BATTERY ANNUNCIATOR
DATA KEYBOARD
STATUS/TEST KEY
Performance Management System Control Display Unit
Figure 6
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ALTERNATE ENGINE
DERATE
PUSHBUTTONS
Performance Management System Limit Select Panel
Figure 7
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TOTAL AIR TEMPERATURE READOUT
Performance Management System Limit Indicator
Figure 8
EFFECTIVITY ALL 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：747飞机维护手册AMM CHAPTER 34 - NAVIGATION 第34章导航4(124)
