Thermal Oxidation Stability of Aviation Turbine Fuels, ASTM D3241 is universally used by the industry to measure high-temperature stability of aviation turbine fuels. The ASTM D3241 is required to be run on every batch of jet fuel produced according to ASTM D1655 or DEF STAN 91-91 specifications. In this test method, the fuel is pumped through heater tube at fixed flow rate and during a specified period of time. The fuel is pass or fail rated according to the amount of deposit formed on the heater tube at a specified temperature. Traditionally, the amount of deposit on the tube is rated visually against a reference color scale. The proper rating requires significant experience and expertise. However, operator capabilities vary, so evaluation of color can be quite subjective