This may be true, but the very concept of this kind of operation is full of errors. The obvious one is that things deteriorate so slow and linear that you will not notice any change. A pilot who flies lots of different aircraft may hear that there is something wrong with one particular engine, but not the owner an daily user of that aircraft/engine.
This is the reason, why a fair warning is for instance increased oil consumption, increased metal in the oil, darker oil at fewer hours and other parameters that can be quantified and thus me monitored quite well. Takes some discipline to monitor the parameters, but that’s what logs are for.
This is the reason, why a fair warning is for instance increased oil consumption, increased metal in the oil, darker oil at fewer hours and other parameters that can be quantified and thus me monitored quite well. Takes some discipline to monitor the parameters, but that’s what logs are for.
I’m sure a full 100% conditional based maintenance is possible (instead of a timely TBO). What I don’t understand is how this somehow is supposed to be cheaper, simpler and ultimately better for everyone than a set TBO. A simple thing as one single cold start at sub zero temperature will totally upset “metal in oil” monitoring. There are too many unknown variables for this to be effective, unless you also have continuous online monitoring of key variables on each engine and a fully operational infrastructure to analyze and do statistics on the data, on all engines.
I agree that keeping logs and manually monitoring the engine will show signs of misbehavior, and is important. But to extrapolate this into saying timely overhaul not necessary, as many people do, is what I don’t understand.
Have run engines on condition past recommended TBO (20%+) – overhauled them when oil consumption was around a quart every four-five hours. Compressions were still good.
Well used engines are fine – I would worry more about hangar queen engines.
Well used engines are fine – I would worry more about hangar queen engines.
I see hangar queens as a particular issue now that the trend is towards more planes than active pilots. Recently a friends E-185 Continental (the predecessor to the O-470 etc) reached a point of burning oil, throwing it out the breather etc and I learned a bit from watching the diagnosis. This particular engine only had a few hundred hours SMOH but over a long period of time because the previous owner got old and eventually gave the plane to the current owner because he trusted him to take care of it. He’s been flying it since and the engine was running fine but using oil.
All the cylinders were pulled on a Saturday (the owner is an A&P) and that allowed inspection of the cam, lifters, bottom end etc. All that stuff looked pretty much like new. A set of new cylinders was investigated but since PMA cylinders aren’t available and these particular Continental cylinders are built in batches, the decision was made to overhaul the existing cylinders. They were given to the finest airboat engine builder 
for diagnosis and assuming all is OK they’ll be overhauled to new spec, signed off by the A&P owner, and reinstalled. The engine should then be good for a long period of private use. Total cost, not as much as you’d think.
Silvaire, why overhaul the cylinders? What is wrong with them? Just hone them and install new piston rings and it should be fine again, barely costs anything if you have access to the machines.
I guess I’ll find out what was needed with the cylinders after the shop inspects them, or when owner gets them back – its interesting to me. I think pistons and rings are relatively cheap, valve and guides can be replaced as needed, plus checking for cracks is a very good idea. I don’t believe the cylinders will get anything they don’t need but no short cuts will be taken. The ‘airboat shop’ (i.e. not a repair station) is actually well equipped and thorough, plus the plane’s owner/A&P doesn’t want to do the job again soon.
In case you’re interested the plane is a Luscombe Silvaire Sedan, a rare beast.
But in the part M crap we have in the UK you can budget on a 700 quid bill for each cylinder that needs replaceimg.
It’s becoming quite a problem these days for flying schools to find suitable aircraft to aid to there fleets due TBO and year limits.
One aicradt I know its engine run out of years in august but it still has 300 hours to go. Its runs lovely such a shame that it will have to be taken off line.
Also the cost in the UK of having an engine overhauled is astronomical.
bq.What I don’t understand is how this somehow is supposed to be cheaper, simpler and ultimately better for everyone than a set TBO Quote
To “overhaul” an engine to zero hours, a number of parts will have to be replaced regardless of condition/dimension, and all accessories will have to be overhauled or replaced. There is the cost, and paying to fix it may have nothing to do with the condition of the core engine.
Ten years ago, my O-200 started making metal in the oil filter. I watched it for a few oil changes, and decided that with more than 3500 hours, it was time to pull it apart to investigate. Once apart, I found the engine immaculate inside. The ONLY non conformance was that one crankshaft journal was .0004" smaller than limit on the power stroke side. As it was apart anyway, I sent it to be ground .010" under, and replace the main bearings. It turned out that the metal had been coming from the crimped on alternator drive coupling all along, hardly a worry at all.
With the engine apart, the shop asked if I wanted it put back together “bulked” to continue on from 3500 +- hours, or “zero’d”. I asked the cost difference. Just over $1000 in mandatory replacement parts, and I would rebuild some accessories. At that point I spent the $1000, just ’cause doing so at that point would increase the value of the plane by more than $10,000.
But none of that in any way affected the operational safety or reliability of the engine in the foreseeable future. We have lots of new technology and investigational capability than they did back when these engine were originally designed and built. We data ourselves to death on the engines, thinking that it is making us safer. Not really, in my opinion. The extra instrumentation (and yes, both my planes have scanners) does help us operate so as to prevent damage (leaning and preventing shock cooling), but otherwise is not as important as simply operating the engine regularly.
The manufacturer’s determination of a TBO number, which then hovers over every engine like a bad cloud, getting darker by the hour, may not be as scientifid as one thinks. The certification block test for an engine is 150 hours of running at a prescribed regime. Any determination of number of hours beyond that is more experienced based. Yet, it is cast in stone. For my experience with O-200’s, the cylinders will never make TBO, replacement or repair will be required part way through, but the "lower end will always make TBO, and then some (unless horribly abused).
I am a strong proponent of “on condition”, and have never had a unsafe condition with a regularly operated engine, which was associated with the number of operating hours. The engines I knew to be worn out, and at the end of life, could safely be flown to the maintenance shop for that work.
To “overhaul” an engine to zero hours, a number of parts will have to be replaced regardless of condition/dimension, and all accessories will have to be overhauled or replaced. There is the cost, and paying to fix it may have nothing to do with the condition of the core engine.
Perhaps that is a commercial practice. This comes up from time to time, and while I’m not familiar with Canadian or EU regulations, under FAA regulations I’m not aware of there being mandatory replacement parts regardless of condition/dimension. An overhaul at its FAA legal minimum consists of disassembling the engine, inspecting and bringing all wear within manufacturer specified service limits, and reassembling. Therefore it is important to know what kind of overhaul was done on an engine, not just that it was overhauled.
FAA Advisory Circular 43-11 covers their terminology: FAA AC 43-11
I also found this link which gives a concise description: Three Kinds of Overhaul
But in the part M crap we have in the UK you can budget on a 700 quid bill for each cylinder that needs replaceimg.
Cylinders cost about $1000 (1000 quid in the UK) anyway. How has Part M affected this?
