This accident report (which I have no comment to make on), page 14 of the PDF...
The oil remaining in the crankcase was black in appearance. An inspection of the latter's oil filter revealed the significant presence of chips, essentially of aluminium and round in shape, 2 to 3 mm in diameter. Their origin could not be determined. A large quantity of metallic particles, mainly aluminium, was also found in the filter section of the oil filter cartridge.
The question of course is how much time (i.e. how many oil changes) there is between seeing the first unusual quantity of metal in the filter and the catastrophic engine failure.
I always cut the filter open (have a special tool) and remove it. Most of the "chips" are carbon flakes and tiny pieces of metal of different type. I think the rule of thumb is up to 1/3 teaspoon is acceptable but it's hard to collect.
Also I remove the little finger with the mesh at the bottom of the crankshaft. There are usually some carbon flakes in there but never seen anything else.
One of the reasons I do my oil changes every 25h is to be able to inspect the filter more often. VFR, I guess I would survive 90% of in-flight engine failures, IFR probably 50%.
Yes - and once a year send an oil sample off to Blackstone's for analysis.
The question of course is how much time (i.e. how many oil changes) there is between seeing the first unusual quantity of metal in the filter and the catastrophic engine failure.
Probably a reasonable number, but if you never do it (which I suspect is true for most people - whether they are expecting it or not) then you will never get the early warning.
I think the rule of thumb is up to 1/3 teaspoon is acceptable but it's hard to collect.
That is far too much metal. An engine should not be breaking up like that. Especially if it is steel. Bits like that will be chewing up the oil pump very nicely.
No, I meant all particles together should not be more than a 1/3 teaspoon. If you get near that, you buy yourself a bigger teaspoon... 
Anytime there is a bigger particle, I would take action. However, getting these small sub 1mm chips is fairly normal.
Anytime there is a bigger particle, I would take action. However, getting these small sub 1mm chips is fairly normal.>
The small bits are normal but they are hard to spot, you also won't know what the metal composition is. I used to send an oil sample every 25h when changing oil. At 50h I used to change oil and filter and send both for analysis.
I had 2 engines failures after o/h to new spec, the first at 75h (noticed a problem at about 60h) and the second 90h after the second o/h (the double gear let a tooth go from the gear that turns the camshaft).
I meant all particles together should not be more than a 1/3 teaspoon
Yes I know
The engine should not be shedding that much metal.
I had 2 engines failures after o/h to new spec, the first at 75h (noticed a problem at about 60h) and the second 90h after the second o/h (the double gear let a tooth go from the gear that turns the camshaft).
I am not sure if you mentioned this before here, but were they done by a particular UK company?
I had 2 engines failures after o/h to new spec, the first at 75h (noticed a problem at about 60h) and the second 90h after the second o/h (the double gear let a tooth go from the gear that turns the camshaft).
Not too surprising, I would say. Most (mechanically induced) engine failures happen in the first 100 hours after overhaul.
If that was true, most of us would have two engine failures, one after the other, as soon as we started flying.
There is a difference between
Most (mechanically induced) engine failures happen in the first 100 hours after overhaul.
and e.g.
Most (mechanically induced) engine failures that happen happen in the first 100 hours after overhaul.
Engine failures (of certified engines) are extremely rare. The calculated MTBF is of the order of 50k hours.
So to get two, it is either extraordinarily bad luck, or something is going on.
Peter, there is no semantic difference between the two statements.
Philip did not make a statement about how frequent engine failures are but that most of these failures tend to happen shortly after an engine teardown.
I would never overhaul an engine based on hours in service or calendar years, the best you can get from that is that it will work as well and reliably as it did before the overhaul.
