Essay on Aircraft Lubrication

Published: 2021/11/30
Number of words: 881

Modern engines used in aircrafts today are very reliable and capable of providing uninterrupted service for years. However, technological advancement in the aviation industry has increased the complexity of these engines (Reciprocating and turbine); therefore, these engines need proper lubrication. The lubrication is required to keep the efficiency of the aircraft engine unaffected from the friction, and the oil acts as the lifeblood for the engines. For instance, if the oil supply stops to the engine parts (example- bearing), or if the oil film breakdown, then the engine could be seized or starts scoring. The continuous supply of oil to the engine is ensured by equipment such as oil pumps, oil filters, and supply lines. It is referred to as the lubrication system. The lubrication system works quietly and continuously like a human heart (Clark, Richards, Hewitt & Langton, 2009). Therefore, it is required to keep the lubrication system of an aircraft healthy and free from all flaws. This research paper focused on the oil filter within the lubrication system and its reason for going into bypass mode. The paper primarily discusses the oil filter and its functions, followed by the reasons and remedies to restore the lubrication system to assure airworthiness in the next flight.

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Aircraft engine oil filter

The oil filters used in aircraft engine oil lubrication are designed to remove solid particles and contaminants from the oil during its circulation through the system. Solid particles in the engine oil could be disastrous during engine operation as they can damage engine parts such as bearings and clog passages and could result in engine failure. In addition, the oil can get contaminated due to operational conditions, for example, a dusty environment, high operating temperature, etc. There are different types of oil filters in aircraft lubrication, and the filtering element comes in a different configuration. Figure 1 shows the schematic representation of an oil filter used in aircraft. It consists of a housing with the filtering element and relief valve. If the filter element is clogged, the filter bypass valve or relief valve diverts the oil flow from the oil filter. The pressure difference was created due to the clogged filter opens the bypass valve. As soon as the bypass valve opens, oil filtering is stopped, and the entire oil flow is bypassed to the engine to avoid the ‘No oil’ scenario (Heiserman, 2015). Although supplying contaminated oil to the engine is also dangerous and could be fatal if care is not taken to restore the filtering function to normal.

Figure 1: Exploded view of aircraft engine oil filter (Heiserman, 2015)

Oil filter bypass

There are primarily two reasons why the oil filtering system goes into the bypass mode (Heiserman, 2015).

  1. Due to the clogged filter element, which creates the pressure differential and opens the relief valve to bypass the engine oil
  2. Increased oil viscosity, mainly during the winter, causes a pressure difference to open the bypass

Procedure to recover from bypass

There are two reasons the engine goes into bypass oil mode; however, there is only one reason for the bypass during the post-flight inspection, which is the clogged filter element. Therefore, changing the oil filter element or entire oil filter depending upon the configuration before clicking the reset on the bypass indicator. Following is the standard procedure to change the oil filter element (FAA, 1998; Caesar, 2018),

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  1. Remove the housing surrounding the engine oil filter
  2. Drin the oil from the bottom
  3. Cut the lock wire and remove the oil filter as well as oil screen
  4. Inspect the screen as well as the filter element
  5. Reinstall the screen, new filter element, and lock wire
  6. Fill in the proper engine oil
  7. Reset the bypass to its original position
  8. Test the engine for its functionality


Lubrication is essential for moving machine parts, especially in aircraft where lives are at stake. This research report introduces the oil filter, its function, along the function of the bypass valve. It also discusses the reason due to which bypass valve actuates. Finally, the standard procedure is listed to replace the engine oil filter element to restore the airworthiness of the aircraft. It is necessary to note that every aircraft has a different oil lubrication system and type of oil filter; this research paper discusses a generalized method to replace the oil filter.

Work cited

Caesar, G. (2018). Aircraft Oil Change. Retrieved from

Clark, C., Richards, L., Hewitt, M., & Langton, R. (2009). Aircraft fuel systems. American Institute of Aeronautics and Astronautics.

FAA (1998). Acceptable methods, techniques, and practices- aircraft inspection and repair. Advisory Circular Title 14 of the code of federal regulations (14 CFR) guidance material43.13-1B (AFS-640), 8.4.

FAA. (1969). Airworthiness compliance check sheet handbook. Department of transportation federal aviation administration8310.6 (FS-340), 17.

Heiserman, D. (2015). Introduction to Aircraft Power Plants. Retrieved from

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