How is Fuel Quantity Gauged?

• A. The fuel quantity in each tank is measured using capacitance gauging transmitters which are excited and interpreted by the signal data computer.
• B. Float sensors in each tank.
• C. Ultrasonic probes.
• D. Manual gauge readings from cockpit.

Answer: (A)

Fuel quantity gauging in this aircraft is done with capacitance-based sensing. Capacitance gauging transmitters are installed in each tank, and the probes form a capacitor whose value changes with the amount of fuel present. An excitation signal is sent into the probes, and the resulting electrical response is read by the signal data computer. The computer uses that response, along with calibration and temperature compensation, to determine the fuel height and convert it into a quantity readout for the crew. This method avoids moving parts inside the tank, offering reliable, accurate measurements across tanks and operating conditions.

Float sensors rely on a mechanical float and potentiometer, which can wear or stick and require more maintenance. Ultrasonic probes measure distance to the fuel surface but are not the standard in this system and can be affected by mounting, tank geometry, or air entrainment. Manual cockpit gauges would not provide in-flight measurements or automatic integration with the aircraft’s fuel management system, making them impractical for actual operation.