Breather tubes

During engine operation, internal combustion generates gases that leak past the piston rings and cause pressure to build inside the crankcase. Without a means of escape, this pressurized engine “blow-by” can lead to blown seals, oil leaks, and major damage—it can even lead to an engine failure. The breather tube serves to vent this excess pressure, along with moisture and other combustion byproducts, and save you from a hefty mechanic’s bill.

There is some variance in routing from aircraft to aircraft, but typically the tube extends sightly upward from the crankcase to prevent excessive oil drippage, then curves down through the cowling and terminates forward of the firewall near the exhaust pipe. Routing near the exhaust can help prevent ice buildup and potentially burn off some of the oil that may be present in the system.

You should visually examine the tube during your preflight inspections or after oil changes, especially if the aircraft is kept outside. Check for blockage and cracks, and make sure the tube is securely attached.

There are a few common issues pilots may encounter. Blockage can be caused by insects or icing. Improper routing of the system can allow water to collect and freeze. Excessive oil discharge is another warning sign and could indicate blockage, worn piston rings or seals, or oil overfill. After a flight, you might notice an unusual amount of oil blown back on the belly of the fuselage and wing struts. Don’t take any chances: If you find an issue, determine the cause, and if necessary, have your mechanic take a look.

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