Lets take as an example that happened at my flying club this past May - and BTW, I flew this aircraft the day before it happened.
The excrept is as follows:
Almost immediately after posting this page, I heard from some knowledgeable friends who were able to draw some tentative conclusions from looking at the photos above. Obviously, the #2 journal was not being lubricated. Possible causes include
particle(s) blocking oil hole from inside
lead sludge in oil blocking oil hole from inside
bearing spun around, blocking oil hole from outside
space aliens
Between the crankshaft and the connecting rod, there is a bearing made of soft metal called babbet. Part of its purpose is to trap tiny particles so they don't scratch the crankshaft or connecting rod, sort of like an ink blotter. This bearing isn't supposed to move. If it does, it can block the oil flow from inside the crank. The resulting lack of lubrication will produce a lot of heat almost immediately - enough to melt the babbet metal. When that happens, a gap opens up between the crank and the connecting rod. This is enough to produce a ticking noise like the one I heard before the engine failed. It doesn't take long before there's enough heat and friction to make the connecting rod jam against the crankshaft. In a case like that, something obviously has to give. If that's what happened to this engine, the connecting rod is what quit next, snapping at the middle. It apparently thrashed around inside the engine for a short while before being flung out the side of the crankcase.
The FAA did send an inspector to look at the plane. He tagged the engine, requiring that an FAA inspector had to be present when any inspection or teardown was done. Since that time, the engine has been removed and transported to the shop that overhauled it. Under the Fed's watchful eye, the overhaul mechanic removed some parts which the FAA will have analyzed. I hope I get to see the results of that analysis. Meanwhile, I have spoken with the inspector.
He told me that the FAA isn't drawing any conclusions yet, which is absolutely understandable. But there is evidence that the locating tang on the rod bearing failed, allowing it to spin and cause the kind of damage I just described above.
We now know that the oil hole was not blocked from inside the crank.
The inspector confirmed that this kind of failure is extremely rare in aircraft engines. He also confirmed that a virtually identical failure appears to be responsible for the downing of another Lycoming-powered airplane (different engine) just three days after my problem happened. What are the odds on that?
The other pilot was not so lucky as I was. He and his wife died that day.
