Question: Why is it that so many training airplanes seem to have perpetual oil leaks? Every airplane at the flight school I train at has a greasy belly. Does this mean they are losing an excessive amount of oil during the flight?
Answer: A greasy belly usually doesn’t mean excessive oil is being lost during flight. Rather, it could be that the oil sump was overfilled. For example, if the engine has a capacity, per the pilot’s operating handbook, of 8 quarts, and it is filled to 8 quarts, you can expect some of that oil to be blown out of the breather tube and down the belly of the aircraft.
In essence, it’s wasted oil, like the foam on the head of a beer.
- READ MORE: Who Can Act as Your Safety Pilot?
- READ MORE: Ditching the CFI Track: Will It Hurt Your Pilot Career?
The oil comes out of the breather tube as a mist and, when it coats the belly of the airplane, it attracts dirt that darkens the stain.
Also, if the flight school you are attending is busy, the airplane likely receives regular maintenance but hasn’t had a bath in a while because it’s so much in use.
If there’s oil covering the engine compartment, that can indicate an oil leak. Or perhaps someone didn’t replace the oil cap tightly enough during the previous flight and the oil hurled all over the engine.
Ask us anything you’ve ever wanted to know about aviation. Our experts in general aviation, flight training, aircraft, avionics, and more may attempt to answer in a future article. Email your questions here.
