Originally Posted by
Pilot DAR
Certainly a part of assuring the airplane is fit for flight. Oil breather pipes have been known to ice over in winter flying conditions - exiting moist air freezes at the exit end of the pipe. For many types there is an AD to assure that a hole is drilled up a little in the pipe to provide an alternate "breather" port in the pipe. That said, the breather allows the constant equalization of crankcase air pressure with atmospheric pressure. If it is blocked, a sign of this will likely be oil being forced out the next easiest path by higher than ambient crank case air pressure. The next easiest crankcase pressure exit path is usually the crankshaft nose seal. If you're having that type of leak in flight, you're going to notice!
One of my colleagues has had two engines problems with blocked breathers in C152s, the last one caused a load of black smoke to come into the cockpit.