Aircraft engines have to be able to work reliably and efficiently in an enormous variety of conditions and in particular, temperatures ranging from over plus 40ﾟon the ground to minus 50ﾟat high altitudes.
A key requirement of aircraft lubrication is that it be responsive to temperature changes and in this regard multi grade oils are now commonplace.
However, the switch to purely synthetic oils, as has happened in the automotive industry, is not recommended for piston aviation engines as the Tetra Ethyl Lead content of exhaust gas does not mix well with synthetic oils. For this reason, most piston engine lubricants are a blend of synthetic and mineral oils.
In addition to lubrication and wear reduction, engine lubricants fulfil an important role in removing the by-products of combustion, as well as cooling the engine. The demands placed on such lubricants are extreme and it is essential that lubrication oils be maintained regularly in terms of replacement of both the oil and the filters. Some manufacturers require just 25 hour oil changes.
It is also strongly recommended that oil analysis is done on old oil to check for any metal that the engine may be making from parts that are beginning to wear. In this regard engine oil analysis is a key safety factor which should be undertaken every time the aircraft is serviced at annual or 100 hour intervals.
In addition, almost all aircraft have hydraulic systems, whether it just be a simple un-boosted braking system, or whether it be elaborate powered flight control systems.
These systems require the correctly specified oil to ensure that the oils are compatible with all the components of the hydraulic susyem, particularly perishable items like rubber hoses, as well as the various different metals associated with the piping and valves and selectors. Again, specialist knowledge is required in terms of making sure that these are maintained in good condition, and without any leaks.