B757 Fuel Calculated vs. Totalizer
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Join Date: Dec 2003
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B757 Fuel Calculated vs. Totalizer
Can any one tell me which fuel quantity is more accurate? If there is a difference between the overhead total and the from the FMC which one should you use? Are there different probes to get these values?
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Join Date: Oct 1999
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Can't help with the 757, but can offer this from the 767. . .
The totaliser quantity is derived from probes in the fuel tanks themselves. The calculated (FMS) value is initially set equal to the totaliser value.
Once the fuel-on signal is received from the fuel control switches during engine start, the FMS then uses fuel flow data to continually reduce the calculated value.
I guess your question concerns which value to place more faith in. All I can suggest is that totaliser value is subject to probe measuring errors, admittedly small in these A/C, whilst the FMS value is only accurate assuming there is no fuel leak between the tanks and the point at which fuel flow is measured.
WG.
Once the fuel-on signal is received from the fuel control switches during engine start, the FMS then uses fuel flow data to continually reduce the calculated value.
I guess your question concerns which value to place more faith in. All I can suggest is that totaliser value is subject to probe measuring errors, admittedly small in these A/C, whilst the FMS value is only accurate assuming there is no fuel leak between the tanks and the point at which fuel flow is measured.
WG.
