Smiths BOEING B737-100 Configuration guide

Smiths Aerospace
Electronic Systems – Malvern
BOEING B737-100/200/300/400/500 Dec. 18, 2002
DOC NO. 0134ED
Rev: F
DIGITAL FUEL QUANTITY INDICATORS
With
TRANSIENT SUPPRESSION UNIT
MAINTENANCE MANUAL
SUPPLEMENT

Smiths Aerospace
Electronic Systems – Malvern
BOEING B737-100/200/300/400/500
INTRO
Page 1
July 15/02
DOC NO. 0134ED
MAINTENANCE MANUAL SUPPLEMENT
CHAPTER 28 – FUEL
INTRODUCTION
Smiths Aerospace, Inc. designed the Transient Suppression Unit (TSU) to produce an alternate means of
compliance to Airworthiness Directive (AD) 99-03-04 which mandates that operators of Boeing B737
aircraft perform wire separation modification to fuel system wiring. The alternate means of compliance is
achieved by the installation of Smiths Aerospace, Inc. Transient Suppression Units(TSU).
The TSU is inserted in the wiring of the Fuel Quantity Indication System (FQIS) between the in-tank
components (capacitance probes and the compensators) and the Fuel Quantity Indicators located in the
cockpit and refueling stations. The TSUs are installed near where the FQIS wiring enters the tanks and
are intended to prevent any electrical signals, current or voltage, which is capable of igniting fuel vapor,
from entering the fuel tank.

Smiths Aerospace
Electronic Systems – Malvern
BOEING B737-100/200/300/400/500
N=NEW PAGE, *=REVISED PAGE, D=DELETED PAGE
REPRODUCTION OF INFORMATION OR ILLUSTRATIONS CONTAINED IN THE PUBLICATION IS
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PAGE 1
Dec 18/02
DOC NO. 0134ED
REV: F
MAINTENANCE MANUAL SUPPLEMENT
CHAPTER 28 – FUEL
LIST OF EFFECTIVE PAGES
E.O. NUMBER
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SECTION
SUBJECT
PAGE
DATE
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Smiths Aerospace
Electronic Systems – Malvern
BOEING B737-100/200/300/400/500
N=NEW PAGE, *=REVISED PAGE, D=DELETED PAGE
REPRODUCTION OF INFORMATION OR ILLUSTRATIONS CONTAINED IN THE PUBLICATION IS
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Smiths Aerospace
Electronic Systems – Malvern
BOEING B737-100/200/300/400/500
N=NEW PAGE, *=REVISED PAGE, D=DELETED PAGE
REPRODUCTION OF INFORMATION OR ILLUSTRATIONS CONTAINED IN THE PUBLICATION IS
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Smiths Aerospace
Electronic Systems – Malvern
BOEING B737-100/200/300/400/500
N=NEW PAGE, *=REVISED PAGE, D=DELETED PAGE
REPRODUCTION OF INFORMATION OR ILLUSTRATIONS CONTAINED IN THE PUBLICATION IS
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Smiths Aerospace
Electronic Systems – Malvern
BOEING B737-100/200/300/400/500
TOC
Page 1
July 15/02
DOC NO. 0134ED
MAINTENANCE MANUAL SUPPLEMENT
CHAPTER 28 – FUEL
TABLE OF CONTENTS
SUBJECT
CHAPTER
SECTION
UNIT
PAGE
EFFECTIVITY
Fuel Quantity Indicating System with
Transient Suppression Unit 28-41-04
Description and Operation 1 All
Trouble Shooting 101 All
Removal/Installation, Fuel Quantity
Indicating System 401 All
Removal/Installation, Fueling Quantity
Indicator 403 All
Removal/Installation, Digital
Calibration Trim Unit 405 All
Removal/Installation, Digital
Calibration Trim Unit Cover and Label 408 All
Removal/Installation, V/Ref Totalizer 411 All
Removal/Installation, Fuel Summation
Unit 412 All
Removal/Installation, Transient
Suppression Unit 414 All
Adjustment/Test Configuration 4.1 501 All
Adjustment/Test Configuration 4.2 501 All
Adjustment/Test Configuration 4.3 501 All

Smiths Aerospace
Electronic Systems – Malvern DOC NO.0134ED
MAINTENANCE MANUAL SUPPLEMENT
BOEING B737-100/200/300/400/500
28-41-04
FUEL QUANTITY INDICATING SYSTEM - DESCRIPTION AND OPERATION
1. General (Fig. 1)
A. The fuel quantity indicating system measures the weight of usable fuel in the fuel tanks. Fuel quantity
indicators on the pilots' instrument panel and refuel quantity indicators at the refuel station on the wing
supply visual indication of the fuel weight in each fuel tank. In addition, a fuel summation unit found
on the first officer's auxiliary panel supplies a continuous summation signal input to an on-board
computer where it is converted to an on-demand display of combined tank total remaining fuel or is
used by the computer in various performance parameters. In the No. 1 and No. 2 tanks, five fuel-
measuring sticks are supplied to find the fuel quantity of the applicable fuel tank by mechanical
means.
B. The overall system is composed of a subsystem for each fuel tank, with components found in the
control cabin, in the fuel tank, and at the refuel station on the wing.
(1) Components in the control cabin include a fuel quantity indicator, digital calibration trim unit
(DCTU), and capacitance trimmer (where applicable) for each fuel tank, an indicator test switch
found above the fuel quantity indicators, and a fuel summation unit or V-Reference totalizer
indicator.
(2) Components at the refuel station on the wing include a refuel quantity indicator for each fuel tank
and an indicator test switch. The refuel quantity indicators repeat the fuel quantity shown by the
fuel quantity indicators in the control cabin. The refuel quantity indicators operate only when the
access door for the refuel station is open.
(3) Each fuel or refuel quantity indicator is "universal" - It can be used to supply indication for any fuel
tank; however, a refuel quantity indicator from the refuel panel on the wing cannot be installed in
the control cabin. Likewise, a fuel quantity indicator from the control cabin cannot be installed in
the refuel panel on the wing.
(4) Components In the fuel tanks include a compensator unit and a number of tank units for each fuel
tank. Fuel measuring sticks are installed In the No. 1 and No. 2 tanks. The tank units in each
fuel tank are connected in parallel and positioned so that only usable fuel is measured.
Capacitance values of the tank units in each fuel tank are added to give a single capacitance
value, which is transmitted to fuel quantity indicator.
(5) Components for electrical protection include the Transient Suppression Units (TSU).
The Transient Suppression Unit (TSU), which incorporates a suppression circuit, is designed to
prevent unsafe electrical signals, either current or voltage from entering the fuel tank.
The TSU is inserted in the Fuel Quantity Indicating System wiring between the in-tank
components and the indicator in the cockpit. The suppression unit is mounted near the specific
tank to be protected.
The suppression circuit is placed in series with the fuel measurement signal leads entering the
tank. The protective circuit of the suppression circuit and the Hi-Z shield are grounded to the
aircraft structure via grounding straps and the attaching hardware at its physical location.
Page 1
Apr 19/02
Airplanes with Smiths 2307 Model Fuel Quantity
Indicators with TSU
EFFECTIVITY

Smiths Aerospace
Electronic Systems – Malvern DOC NO.0134ED
MAINTENANCE MANUAL SUPPLEMENT
BOEING B737-100/200/300/400/500
28-41-04
Fuel Quantity Indicating System Component Location
EFFECTIVITY Figure 1 (Sheet 1)
Page 2
Apr 19/02
Airplanes with Smiths 2307 Model Fuel Quantity
Indicators with TSU

Smiths Aerospace
Electronic Systems – Malvern DOC NO.0134ED
MAINTENANCE MANUAL SUPPLEMENT
BOEING B737-100/200/300/400/500
28-41-04
Fuel Quantity Indicating System Component Location
Figure 1 (Sheet 2)
Page 3
Apr 19/02
Airplanes with Smiths 2307 Model Fuel Quantity
Indicators with TSU
EFFECTIVITY

Smiths Aerospace
Electronic Systems – Malvern DOC NO.0134ED
MAINTENANCE MANUAL SUPPLEMENT
BOEING B737-100/200/300/400/500
28-41-04
Fuel Quantity Indicating System Component Location
Figure 2
Page 4
Apr 19/02
Airplanes with Smiths 2307 Model Fuel Quantity
Indicators with TSU
EFFECTIVITY

Smiths Aerospace
Electronic Systems – Malvern DOC NO.0134ED
MAINTENANCE MANUAL SUPPLEMENT
BOEING B737-100/200/300/400/500
28-41-04
Fuel Quantity Indicating System Component Location
Figure 3 (Sheet 1)
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Apr 19/02
Airplanes with Smiths 2307 Model Fuel Quantity
Indicators with TSU
EFFECTIVITY

Smiths Aerospace
Electronic Systems – Malvern DOC NO.0134ED
MAINTENANCE MANUAL SUPPLEMENT
BOEING B737-100/200/300/400/500
28-41-04
Fuel Quantity Indicating System Component Location
Figure 3 (Sheet 2)
Page 6
Apr 19/02
Airplanes with Smiths 2307 Model Fuel Quantity
Indicators with TSU
EFFECTIVITY

Smiths Aerospace
Electronic Systems – Malvern DOC NO.0134ED
MAINTENANCE MANUAL SUPPLEMENT
BOEING B737-100/200/300/400/500
28-41-04
Fuel Measuring Stick Extended Position (Example)
Figure 4
EFFECTIVITY
Page 7
Apr 19/02
Airplanes with Smiths 2307 Model Fuel Quantity
Indicators with TSU

Smiths Aerospace
Electronic Systems – Malvern DOC NO.0134ED
MAINTENANCE MANUAL SUPPLEMENT
BOEING B737-100/200/300/400/500
28-41-04
Fuel Quantity Indicating System Component Location
Figure 5
Page 8
Apr 19/02
Airplanes with Smiths 2307 Model Fuel Quantity
Indicators with TSU
EFFECTIVITY

Smiths Aerospace
Electronic Systems – Malvern DOC NO.0134ED
MAINTENANCE MANUAL SUPPLEMENT
BOEING B737-100/200/300/400/500
28-41-04
Fuel Quantity Indicating System Schematic
Figure 6 (Sheet 1)
Page 9
Apr 19/02
Airplanes with Smiths 2307 Model Fuel Quantity
Indicators with TSU
EFFECTIVITY

Smiths Aerospace
Electronic Systems – Malvern DOC NO.0134ED
MAINTENANCE MANUAL SUPPLEMENT
BOEING B737-100/200/300/400/500
28-41-04
Fuel Quantity Indicating System Schematic
Figure 6 (Sheet 2)
EFFECTIVITY
Page 10
Apr 19/02
Airplanes with Smiths 2307 Model Fuel Quantity
Indicators with TSU

Smiths Aerospace
Electronic Systems – Malvern DOC NO.0134ED
MAINTENANCE MANUAL SUPPLEMENT
BOEING B737-100/200/300/400/500
28-41-04
Fuel Quantity Indicating System Schematic
Figure 6 (Sheet 3)
EFFECTIVITY
2. Tank Unit (Fig. 3)
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Airplanes with Smiths 2307 Model Fuel Quantity
Indicators with TSU

Smiths Aerospace
Electronic Systems – Malvern DOC NO.0134ED
MAINTENANCE MANUAL SUPPLEMENT
BOEING B737-100/200/300/400/500
28-41-04
A. The tank units are cylindrical capacitors which are installed throughout each fuel tank to sense fuel
level variations and, as a result of capacitance change, transmit electrical signals to the fuel quantity
indicators. The tank units have two coaxial cylinders which are rigidly spaced at intervals throughout
their length by insulating centering spacers. The inner electrode is a variable diameter nickel alloy
tube and is connected to the Hi-Z input. The outer electrode is an aluminum alloy tube of constant
diameter and is connected to the Lo-Z voltage excitation lead. The diameter of the inner electrode is
profiled to supply an output signal which is linear with respect to the volume of the fuel in the tank.
Openings at the ends of the tank units let fuel assume the same level between the two cylinders as
that in the fuel tank.
B. Changes in airplane attitude can cause errors in the fuel quantity measurement. The tank units are
installed in locations in the fuel tank that keep these errors to a minimum. The large number of tank
units in different locations in the fuel tank also keeps these errors to a minimum.
C. Tank units are attached to wing ribs in the No. 1 and No. 2 tanks and to spanwise beams in the center
tank. Access to the tank units is through fuel tank access openings. Electrical connections to the tank
units are made at the tank unit terminals. Tank unit leads in a given fuel tank, form a harness that
terminates at a receptacle. The receptacles for the No. 1 and No. 2 tanks are found in the front spar
of the applicable wing, and for the center tank in the forward bulkhead of the wheel well for the main
landing gear on the left side. Connected to each receptacle is a bussing plug assembly. The bussing
plug assembly connects the tank units in parallel.
3. Compensator Unit (Fig. 3)
A. The compensator unit in each fuel tank acts as a sensing element to maintain a linear relationship
between fuel dielectric properties and fuel density. Each compensator unit has a low impedance plate
and two high impedance plates, which are protected by a mechanical shield. The compensators are
attached to the same wing structure as the tank units and are installed so that they are completely
submerged in fuel at all times. Access to the compensator units is through the fuel tank access
openings. Leads from the compensator units are contained in the same harness used for the tank
units.
4.
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Airplanes with Smiths 2307 Model Fuel Quantity
Indicators with TSU
EFFECTIVITY

Smiths Aerospace
Electronic Systems – Malvern DOC NO.0134ED
MAINTENANCE MANUAL SUPPLEMENT
BOEING B737-100/200/300/400/500
28-41-04
Fuel Quantity Indicator (Fig. 1)
A. Digital fuel quantity indicators show the weight of fuel in each fuel tank. Each fuel quantity indicator
has a single chip microcomputer system and a digital liquid crystal display (LCD). The microcomputer
measures capacitive and resistive (electrical leakage due to contamination or water) current in the
tank units. The microcomputer also monitors other circuit parameters. When a parameter reaches
an unacceptable level for at least 30 seconds ERR is shown on the indicator face, with a blank, zero
or normal fuel quantity reading as specified below. If an intermittent fault disappears for at least 30
seconds the ERR display is blanked, but the error code remains logged in indicator memory. If the
indicator has a normal display, when the indicator test switch is activated the display will show ERR
plus all stored error codes (between 1 and 10) which will be used to help in troubleshooting the
system. If a zero or blank display is present, the power to the indicator must be cycled to read the
error codes. The subsequent define the error codes.
ERROR FUEL QUANTITY PROBABLE
CODE INDICATOR READING CAUSE
1 Normal An open circuit or a short circuit
in the COMP LO-Z wiring *[2]
2 Zero A short circuit in the compensator
unit (HI-Z to COMP LO-Z)
3 Normal Too much leakage in the
compensator unit
4 Zero An open circuit or short to ground in
one of the LO-Z wires to the tank
units *[2], [3]
5 Zero A short circuit in one of the
tank units (HI-Z to TANK LO-Z)
6 Normal Too much leakage in a tank unit
7 *[1] Digital Calibration Trim Unit does
not operate correctly
8 Blank An error in the DCTU data
9 *[1] A problem with the indicator
memory
10 Zero An open circuit or a short circuit
in the HI-Z line *[2]
*[1] If a problem occurs during flight, the indicator will continue to show a normal value with ERR also
shown. If a problem occurs when power is applied, the indicator will show zero with ERR also shown.
*[2] These error codes can also be caused by these conditions occurring internal to the TSU.
*[3] Holding the test switch for longer than 30 seconds will log error code 4.
B. To clear all stored error codes, including those stored by activating the self test switches, push the
indicator test switch until the display goes to zero, release the indicator test switch, then push the
indicator test switch again while the fuel quantity indicator is in self test mode. The fuel quantity
indicator will complete self-test cycle and show the word CLr.
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Airplanes with Smiths 2307 Model Fuel Quantity
Indicators with TSU
EFFECTIVITY