From the "Professional Pilot" site:
Thrust Specific Fuel Consumption (TSFC)
Thrust Specific Fuel Consumption (TSFC) is defined as the ratio of fuel flow to thrust produced by the engine:
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For JET engines TSFC is very close to being constant over a wide range of airspeeds. In other words the same amount of fuel flow produces the same amount of thrust at any speed from zero to close to the speed of sound.
We must emphasize the above point: TSFC is very close to being constant for a JET engine. This is a critical point. It means that to determine the fuel flow we simply use the formula: FF = TSFC x Ta. Given that TSFC is a constant this is a very useful and powerful equation. Let's emphasize it again:
From Boeing Jet Transport Performance Methods:
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