Contaminated oil can degrade and corrode dynamic and flight critical aircraft components. Thus, oil change timing becomes critical. The ability to instantaneously ascertain comprehensive operating oil conditions real-time on an aircraft allows the user to change the oil at the optimum schedule (avoid wasting oil); but more importantly, provides valuable maintenance insight as an early warning indicator of abnormal conditions when unexpected contaminants are detected. Known methods of determining e.g. lubricating oil quality embrace Infrared Spectroscopy, Viscosity Measurement, pH Measurement, or Prediction of Degradation technologies.

Measuring the quality of the oil by Infrared Spectroscopy has the advantage of determining many qualities of the oil other than lubricity. Unfortunately, for acceptable results the current method requires removing a sample of the oil from the vehicle and placing it in an infrared spectroscopy instrument. The instrument is expensive and requires some dexterity and experience with scientific measurements to use. Thus is not a suitable method for alerting one that the oil needs to be changed. Additional disadvantages for the current method include possible sampling errors (a clean sample of the same oil type must be supplied for proper analysis of the used oil), and the time lag for obtaining results. A major problem with attempting to utilize infrared technology in a continuous real-time oil monitoring environment is the unavoidable accumulation of contaminants on the sensor surface which decreases its accuracy; conversely, a maintenance free method (GA Alert, Aviation Oil Advantage) is preferred by which the normal operational accumulation of contaminants on the sensor surface is desirable and essentially monitored and interpreted as part of the oil monitoring algorithm to increase continuous real-time oil analysis accuracy.

A decrease or increase in oil Viscosity is a reasonable indicator of oil contamination or oxidation; however, interpretation of the measured relative effects of oxidation, fuel, or water contamination can be misleading; also, viscosity changes due to oil breakdown that happens after oxidation. The Aviation Oil Advantage method is totally independent of oils viscosity and measures oxidation as a proactive indication of degrading oil conditions prior to oil breakdown.

Although the pH of an oil gives an indication that something is wrong with the oil, the pH does not directly measure the oil lubricating quality, but merely measures the presence of acids in the oil; and does not determine that the oil has degraded if the oil is contaminated by water or metal particulate. Basing oil quality on pH measurements can also be unreliable. Volatile acids can evaporate over extended periods at operating temperatures and give a pH reading inconsistent with oil quality. The pH sensor apparatus is expensive and not particularly suited for the environment of the oil pan of an engine or gearbox.

Prediction methods for periodic oil degradation (based on time, mileage, or predictive algorithm) do not take into account the quality of the clean oil (synthetic, multi-grade, API certified, specific additive formulation), nor does it take into account the actual operating conditions/malfunctions that directly effect the oil condition. Further, it does not account for engine wear as a factor in oil degradation. This method has recently become more sophisticated; however it is still simply a prediction that provides no qualitative or quantitative information regarding actual oil condition.