The Visual Rating method and the ALCOR Mark 8A Tube Deposit Rater, used to rate deposits that form on the Jet Fuel Thermal Oxidation Tester (JFTOT) heater tubes, were compared to each other and to measurements of the deposit thickness. An Auger Electron Spectrometer, used in conjunction with an ion gun (AES/Ion Gun), was used to measure the deposit thickness and composition. Both the Visual Rating method and the Mark 8A Tube Deposit Rater were found to correlate with deposit thickness measurements to a limited degree. The AES/Ion Gun method proved to be a useful laboratory tool for measuring the relative thickness of deposits and the elemental composition of deposits (except for hydrogen and helium). Deposits that have a spectrum of colors (i.e., peacock or rainbow type deposits) were found to be considerably thicker than Code 3 deposits. Thin film light interference was found to be the cause of the peacock associated with these deposits.

Quantification of deposits formed of heated metal surfaces is desirable for the evaluation of thermal stability by the JFTOT procedure. Empirical methods widely employed entail either visual comparisons or measurements of reflected light (TDR), both of which are sensitive to deposit color. We have examined these and several other measurement techniques for JFTOT heater tubes and have found that measurements of total carbon content by combustion were the most reliable. Two novel techniques, based on measurements of dielectric strength and interference effects of monochromatic light have been examined. It was found that the dielectric and interference methods correlated well with the combustion analyses and each other, while the TDR often yielded misleading results. The correlations between the various methods will be discussed in addition to the consequence of method choice on the interpretation of experimental data. Keywords: Jet fuels, Thermal oxidation stability, Tube deposit rating methods.

For technical readers in the aviation and fuel industries, and in testing laboratories, explores the history and philosophy of the thermal stability of aviation fuel, and considerations during the fuel's manufacture, storage and transport, use, and assessment. The 13 papers, representing a number of