Abstract: The real time measurement of the aircraft fuel density is crucial in the aircraft Fuel Quantity Indication System (FQIS). This paper introduced the principle of using the radioactive isotope gamma rays to measure the aircraft fuel density. The results of density measuring experiments using in LAB measuring system have proved that this method is not only feasible, but also precise enough to be applied widely to real time aircraft fuel density measurement.

Key words: radioactive isotope, gamma rays, aircraft fuel, density measurement