Peter wrote:
It would be crazy to be making say 500ppm aluminium and fly the plane.
If you had anywhere near 500 ppm al. you would have a filter full of crap to prove it long before the lab results came back …
are you going to stop flying with just the high spec analysis results
If they were high enough I would have the engine rebuilt, yes.
It would be crazy to be making say 500ppm aluminium and fly the plane.
With iron, you could get that with a rusted engine (a hangar queen) but it should progressively improve, while you check periodically for scored cylinders etc.
Sure Peter, but I go back to my original remark: are you going to stop flying with just the high spec analysis results ???
Probably not, that is until it is backed-up with junk in the filter …
Not entirely, because small particles will not be visible in the filter, even if they do get stuck in it.
Oil analysis detects microscopic stuff (e.g. caused by a lack of lubrication to some bearing).
The filter will pick up pieces of metal which have actually broken off somewhere.
The strainer will pick up large chunks of metal. These could also end up in the oil filter.
You could have a long term bearing problem which never produces anything which a human will see in the filter. One could argue that all the time the bearing doesn’t “explode” you are good to fly, but that would be an interesting (if not unusual) attitude to risk management 
So what good is it then ?
I mean the decison tree is so bloody simple :
Change oil – take sample & open filter
Nothing in filter = keep flying
Nothing in analysis = keep flying
Something in filter = stop flying
Something in analysis = see filter
I would say no sh1t Sherlock
It goes without saying that if your metals keep rising then there must be a reason. And people should be looking in the oil filter (and on Lycos the strainer too) anyway.
So while oil analysis itself doesn’t tell you much, it tells you what to do next. Unnervingly close to a PSA test actually….
I was reviewing the Lycoming Service Instruction 1492D pertaing to piston pin cap wear and thought I would copy the part about Oil Analysis.
The take-away here is simple: if alminum goes up – check your oil filter for junk ! Oh yeah, you should be checking your filter anyways … 
Peter wrote:
I am not going to do anything, at this level or anywhere near it.
Precisely and that’s why I consider oil analysis just one tick above being completely useless.
The scenario is almost always the same: you perform an oil change, the results come back a few days later, such & such levels are up, but you just finished the 25h, 50h or whatever inspection routine and hopefully you’ve checked the oil filter contents. With nothing in the filter and no other anamolies found, you soldier on wondering what’s causing the high(er] levels of [whatever] …
why are you keeping the oil level low?
It is still in spec – see here
And anything above about 10 is lost from the breather.
Oil analysis is just one tool in the box of engine condition monitoring.
Sure. The filter and the strainer will pick up larger pieces but they are clean.
I have seen people change the oil ( and not record this ) just before a buyer gets an aircraft inspected prior to purchase, the analysis comes back clean but this usually hides a multitude of problems in the engine as the analysis is based on the assumption that the oil has run about 50 hours in the engine with only normal oil consumption.
Based on what I have seen I think this may be quite common in for-sale aircraft, but I don’t mean necessarily covertly. Also if you are buying a low-time plane, say a hangar queen with 2hrs in the past year, and the oil+filter has been changed every year, there is no point in checking them.
It is the overall condition of the oil that is the thing to watch not just the oil spectro analysis, Michael’s example of wrist pin pin plugs ( piston pin plugs ) giving high aluminum levels might not be a reason to start pulling cylinders but chips of aluminum in the oil filter would be, as these chips are so large it is likely that due to them being filtered by the oil filter the oil spectro analysis alone will show the true magnitude of the problem.
Oil analysis is just one tool in the box of engine condition monitoring.
I have seen people change the oil ( and not record this ) just before a buyer gets an aircraft inspected prior to purchase, the analysis comes back clean but this usually hides a multitude of problems in the engine as the analysis is based on the assumption that the oil has run about 50 hours in the engine with only normal oil consumption.
