Smiths Aerospace
Electronic Systems – Malvern
DOC NO.0134ED
MAINTENANCE MANUAL SUPPLEMENT
BOEING B737-100/200/300/400/500
28-41-04
5. Refuel Quantity Indicator (Fig. 2)
A. Refuel quantity indicators on the P15 panel show the weight of fuel in the fuel tanks. The refuel
quantity indicators function as repeaters of the fuel quantity indicators found in the control cabin and
help the ground crew in refuel or defueling operations. The refuel quantity indicators are
interchangeable with each other. The refuel quantity indicators operate only when the access door
for the refuel station is open. When the access door is closed, power to the refuel quantity indicators
is interrupted by a proximity switch
B. The refuel quantity indicators monitor the signal received from the fuel quantity indicators and show
an error code if a system malfunction exists. The subsequent table lists the error codes and their
probable causes.
TYPE 2101 REFUEL QUANTITY INDICATOR
EFFECTIVITY
ERROR REFUEL
QUANTITY
PROBABLE
CODE
INDICATOR READING
CAUSE
7
“0” Zero
Signal from fuel quantity
indicator erroneous or missing
NOTE:
When the indicator test switch on the P15 panel is activated, the refuel quantity indicators
show ERR and log error code 7 into memory. Fuel quantity indicators in the flight
compartment show ERR and log error code 1 into memory if the switch is held for at least
30 seconds.
TYPE 2120 REFUEL QUANTITY INDICATOR
ERROR REFUEL
QUANTITY
PROBABLE
CODE
INDICATOR READING
CAUSE
5
“0” Zero
Bad indicator
6
“0” Zero
Bad indicator
7
“0” Zero
Fuel quantity indicator shows an
error
8
“0” Zero
Signal from fuel quantity
indicator erroneous or missing
NOTE:
When the indicator test switch on the P15 panel is activated, the refuel quantity indicators
show ERR and log error code 8 into memory. Fuel quantity indicators in the flight
compartment show ERR and log error code 1 into memory if the switch is held for at least
30 seconds.
6. Fuel Summation Unit (Where Applicable)(Fig. 1)
A. The fuel summation unit takes the digitally encoded signals on the compensator Lo-Z line for each
fuel quantity indicator and adds them for a total fuel quantity. This total quantity is then used to
generate an output voltage signal representative of the total fuel remaining. This output signal is one
of several inputs to a Flight Management Computer System (FMCS) or a Performance Data
Computer System (PDCS) that has a control display unit (CDU). The PDCS will display the
instantaneous total fuel remaining when the mode selector knob is positioned on STBY and key No. 6
is depressed (Ref. Ch. 34). The FMCS also provides a display of total fuel remaining (Ref 34-62-
00/001).
Page 14
Dec 18/02
Airplanes with Smiths 2307 Model Fuel Quantity
Indicators with TSU
