The other day, I watched someone taxi up and the first thing he did was open the oil door and take off the cap.  I (politely, of course :-) asked him why he did that, to which he replied, "look at all those fumes - I'm letting them out."  And I then read in the last Lancair post, ".... and crankcase always vented after flying."  Is this a normal thing to do?  In 40 years of flying I've only seen it done once and never heard of the practice before or since.  I can't imagine that opening the cap does much to change the atmosphere in the crankcase.  Is there any test data or theory to support the practice?  I'll admit that I'm a bit paranoid - If I check the oil and find I need some, I'll carefully replace the cap (assuming the dipstick is part of the cap), go get the oil and then take the cap back off to pour it in.

I try to never walk away, leaving anything in an unairworthy condition assuming I'll come back and fix it later.  Maybe it goes way back to when someone took off from the local airport, noticed oil coming from the cowling (of a twin), realized that he had left off an oil cap, shut the engine down, overflew several good airports to come back, came in high, made a go-round, botched it, and you know the rest.  One of the well-known test pilots did my first flight.  He was casually (correction - I don't think anything he does is "casual") watching me replace the plugs.  I hand-tightened the wires and walked away to get a wrench.  He about had a heart attack and chastised me for walking away with parts of the plane looking like they were attached, but weren't.  He said "get the wrench first, then put the wires on."

Gary Casey