Oil analysis is a tool that can be used by the owner and maintenance personnel to make more informed decisions as to the current condition of an engine.
The parts used in aircraft engines are made from a number of different metals and alloys (pistons are made from an aluminium alloy, cylinder barrels are generally steel, piston rings have a chrome face, main bearings are made from an alloy of copper, tin and lead, connecting rod bushes are bronze etc). In operation all these parts wear slightly, depositing minute particles of the metal in the oil.
Oil Analysis programs generally test for nine different substances: copper, iron, chromium, lead, tin, aluminium, silicon, molybdenum and sodium. The wear metal particle concentrations are usually expressed in parts per million (PPM)
If wear of a particular part accelerates then the concentration of wear metal particles increases, signalling a problem.
Analysis of the various levels of the individual wear metals assists in identifying the part that is wearing at the accelerated rate.
Oil analysis assists in detecting problems early so minor problems can be repaired before more expensive repairs are required or a major failure occurs. For example high levels of silicon in the oil can indicate that dirt is entering the engine. Fixing the air cleaner is cheaper and easier that having to overhaul the cylinders after the dirt has caused wear to the piston, rings and cylinder barrel.
The major advantage of oil analysis is confidence. As long as the level of the various wear metal elements is fairly consistent over time and do not show a sharp rise, the operator can be reasonably confident that the engine was operating normally when the oil sample was taken.
Oil Analysis Limitations
Oil analysis provides a good guide as to the wear that is occurring in an engine but it does have limitations. For example as oil analysis is based on examining the concentrations or various substances in the used engine oil, it will not predict the sudden breakage or fracture of a part.
Some caution is also required when comparisons between different oil samples are made. Changes to the type of use, sampling procedures and seasonal changes can all result in variations to the wear levels in the oil sample.