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 28-41-00
 ú CONFIG ú 09 Page 34 ú May 28/99

A

757
MAINTENANCE MANUAL

 (6)  
Indicator Signals

 (a)  
The FQPU computes the weight of fuel in each fuel tank. The FQPU also computes the total fuel, by summing the quantity of fuel in each individual tank.

 (b)  
The quantity of fuel is shown digitally on the fuel quantity indicator found on the overhead panel, P5. The fuel quantity indicator has individual displays for each fuel tank and for the total fuel quantity. The fuel quantity indicator also shows the fuel temperature (AMM 28-43-00/001).

 (c)  
If the FQPU determines that there is unknown accuracy in a fuel quantity indicator, it will blank the individual indicator in the flight compartment and on the fueling control panel, P28. The total fuel quantity indicator on the P5 panel and on the flight management computer will also be blanked.

 (d)  
With the fueling station door open, the top half of the individual load select indicators show the quantity of fuel in their respective tanks.

 (7)  
FQIS Fueling Control

 (a)  
With power supplied to the FQIS and the load select control set to the quantity of fuel required, an analog signal proportional to that amount, is sent to the FQPU. The FQPU digitizes the signal and stores it in memory. The FQPU also sends a digital signal of the same value to the load select indicator, for display on the bottom readout display. As the airplane is fueled, the fuel quantity is shown on the top display. When the selected quantity of fuel displayed on the bottom display is reached, the fueling shutoff valves close.

 (8)  
FQIS Fault Recovery

 (a)  
Two independent channels of on-line electronics are provided, so if a fault occurs in one channel automatic switchover to the other channel occurs.

 (b)  
Loss of power also causes automatic changeover to the other power supply.

 (c)  
If a tank unit is contaminated, the computer calculates an average value from the other tank units in the same tank.

 (d)  
If a densitometer fails a densitometer in one of the other tanks is used.

 (9)  
FQIS Fault Detection

 (a)  
The FQPU carries out almost all fault detection on the FQIS automatically. The FQPU continuously tests the system and its components, while the FQIS functions. If a fault is detected, an EICAS maintenance message, FUEL QTY BITE, is shown and the fault is stored in the computer memory for recall by the maintenance crew.
　
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