Definition
A fuel quantity indicating system that measures fuel by mass rather than volume, using tank-mounted probes that act as electrical capacitors. Each probe consists of two concentric metal tubes separated by the fuel and air between them. As fuel level changes, the dielectric (insulating) properties between the tubes change, altering the probe's capacitance. The system converts these capacitance changes into a cockpit indication of fuel quantity, typically in pounds.
Plain English
A fuel gauge system that uses electrical sensors inside the tanks to figure out how much fuel is on board by weight. The sensors detect the difference between fuel and air around them and send that information to the gauge in the cockpit.
Context Anchor
Seen in aircraft fuel quantity indication systems, especially during fuel gauge checks, troubleshooting, and fuel tank maintenance.
Derivation
Capacitance comes from the Latin capacitas, meaning 'ability to hold.' In electronics, a capacitor is a device that holds an electrical charge between two conductive surfaces separated by an insulator. The fuel tank probes work the same way -- the fuel and air between the tubes act as the insulator, and how much charge the probe can hold tells the system how much fuel is present.
Why Pilots Care
Provides reliable fuel quantity data critical for flight safety and fuel management.
Grounding Statement
As more of the tank probe is covered by fuel, the electrical reading changes, and the system turns that change into a fuel quantity indication.
Intuition Check
Do not assume this system measures fuel by weight or by a float moving up and down. It measures an electrical change caused by the amount of fuel around the tank probes.
Example Sentence 1
The capacitance-type fuel quantity measuring system reads in pounds because it measures fuel mass, which is what matters for performance calculations.
Example Sentence 2
Accurate readings from the capacitance-type fuel quantity measuring system helped the pilot plan the remaining flight time.