Managing oil streaks. spills and leaks

If you rent aircraft or are undergoing training, you must've come across evidence of an oily surface, or belly of an aircraft or even as far back as oil on the tailskid or tie down point. There is an addage that says a leak as such is not a problem, it is the change in the leak that should be concerning.

The sad truth is that many rental pilots just ignore this and move on. Changing this attitude is a task and must become a culture for it to be self-sustaining. 

Is also an excellent example of the level of airmanship, but it also reflects on general knowledge and exposure. 

So, what must you do if you observe evidence of engine oil on an airframe.

Identify sources of oil
Clean the evidence
Monitor the recurrence of the evidence



The bottom line is, that if you don’t clean up any oil that you see on the airframe, how would you know if the leak is bad? Most evidence seen on airframes from my experience, is due to pilots spilling oil in the cowling when trying to top up engine oil. Not using a funnel, or trying to do it in wind. You only need to spill a table spoon of oil to end up with a sticky fuselage!

Lets explore some reasons a bit:

1. Oil cap not secured happens sometimes and is just plain embarrassing. The cause is obvious and the cowl will need removal for cleaning.






2. Pin-hole leak in a high pressure line will typically occur as a spray of fine mist. 

The sprayed oil will probably be found in unlikely spill areas. Maintenance will be required for this.


3. A severe leak will be obvious, however may not be obvious in flight, unless the leak is observed, like oil runnin up onto the windshield. 

The actual amount of oil lost can be small but cause a huge amount of slick covered airframe. Maintenance will be required for this.

4. Variable pitch propellers can leak oil if a seal is damaged or if there is excessive play on the hub bearings. Always check the back of the blades. Oil runs are slick and shiny. Grease splatter can also be observed and will be black/blue and sticky. This is often found after maintenance has repacked the grease for the hub bearings. 

An oil leak here requires maintenance attention.




5. Crankcase breather is an open exit from crank case, and serves as a crankcase pressure relief and it is also an exit for oil vapor. This is normal and droplets of oil can form and drip from this pipe.

Overfilling the oil will result in more oil exiting here, but generally the vapor will only lead to a very thin and tacky surface that traps dust.


7. Example of an uncleaned aircraft where this aircraft was flown for days with this evidence. It displays poor airmanship and shows no regard for equipment. Pilots are not taking ownership of their actions and do not seem to regard this as an issue. It may also be lack of understanding or exposure to the dangers of ignoring this, or thinking someone else is employed to clean. It is totally unacceptable to fly like this.

Oil Spill Evidence that is light coloured oil is most likely spillage blowing out from cowl. Clean the area with a rag and a little degreaser (or AVGAS). Ensure you rub the surface dry after cleaning, and inspect again after flight. If there is more spill, clean it again. Make sure you pass the information on to the next crew, so that they can also monitor.

Deeper cleaning of a spill may be needed. Spilled oil will blow out during flight and the cowling may need cleaning on the inside. You can clean it to a certain degree while it is on the airplane, but a proper job will require removal first. 

Oil is also captured between panels and acts as an abrasion aid. Such abrasion shows as thin streaks of very grey/black oil, eminating from a faster position or panel lapping point.

In closing there is an interesting read available Called

"A sticky situation: Air Facts Report"

https://airfactsjournal.com/2017/05/sticky-situation-flying-blind-vintage-airplane


My closing statement is that you all keep it clean!


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