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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
D. These are some of the usual causes of bad values on the FQIS:
(1)
Large quantities of water collect in fuel tanks and cause a short circuit in the tank units and the compensator units.
(2)
Blocked drain holes in the spanwise stringers in the wing tanks which can prevent the flow of water to the sumps.
(3)
Microbes, fungus, and contamination in the internal structure of the fuel tank and on the tank units and the compensator units.
(4)
One of the tank units has a short circuit to ground because it touches the structure, tubing, or bonding straps in the fuel tank.
(5)
The circuit for the electrical signal from the tank unit is open or intermittent because of these problems:
(a)
A terminal screw that is not installed.
(b)
A terminal screw is loose.
(c)
The incorrect terminal screw was installed.
(d)
There is internal damage to the tank unit because there is too much torque on the terminal screw (too tight). Refer to AMM 28-41-21/401 for the torque specifications.
(6)
There is a short circuit between the compensator elements, the high Z elements, and the low Z elements.
(7)
There is a broken wire in the electrical harness for the tank units that gives an intermittently open-circuit.
(8)
A bad O-ring seal installation at the spar receptacle or the bussing plug. This permits fuel to leak from the tank to the face of the connector and (or) water to go on the face of the connector. One of these conditions can cause a leakage path between connector pins and change the system capacitance values.
(9)
Fuel goes through the wire harness for the tank units to the face of spar receptacle which can cause changes in the system capacitance.
(10)
Bad connections in the connectors between the indicator and the tank.
(11)
Indicators that show unusual values because the pointer on an indicator does not move freely because it is not lubricated correctly.
(12)
This table gives a summary of the most usual fault indications and their causes:
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28-41-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
~........................................................................ | FAULT | CAUSE OF THE FAULT | | INDICATION | | ..........................................................................
| The indicator in the flight compartment | Short Hi-Z to Lo-Z |
| goes to the high end of the scale. | |
| The refuel indicator follows. | |
.......................................................................... | The indicator in the flight compartment | Short Hi-Z to Ground | | goes to the high end of the scale. | | The refuel indicator follows. | | .......................................................................... | The indicator in the flight compartment | Short Lo-Z to Ground | | goes to the low end of the scale. | (probe hitting frame or | | The refuel indicator reads the same as | plumbing in tank) | | the flight compartment indicator. | | .......................................................................... | The indicator in the flight compartment | Short compensator | | reads HIGH or pegs at the top stop. | Lo-Z to ground | | The refuel indicator reads LOW or pegs at | | | the bottom stop. | | .......................................................................... | The indicator in the flight compartment | Short compensator Lo-Z | | reads LOW. Probably at the bottom stop. | to Hi-Z (water in | | Depends on resistance in short. Unstable | compensator) | | if water is present. | | .......................................................................... | The indicator in the flight compartment | Open Hi-Z | | goes to the high end of the scale. | | | The refuel indicator follows. | | .......................................................................... | The indicator in the flight compartment | Open Lo-Z | | goes to the low end of the scale. | | | The refuel indicator follows. | | .......................................................................... | The indicator in the flight compartment | Open Comp Lo-Z | | reads HIGH. | | | The refuel indicator reads LOW. | | .......................................................................... | The indicator in the flight compartment | Open shield | | reads HIGH. | | | The refuel indicator follows the flight | | | compartment indicator (normal) | | 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：737-300 400 500 AMM 飞机维护手册 燃油 FUEL 3(37)
