Flying Beyond Engine TBO

[neilharris360]

What must be done for a privatly owned aircraft to be flown beyond engine TBO and how long beyond can it be flown.

[Hedley]

Nothing, and forever. See CAR 625 App C(7)

http://www.tc.gc.ca/eng/civilaviation/r ... c-2460.htm

No hard time, including calendar time, between overhauls need be observed in the case of small aircraft reciprocating engines in non-commercial private operation

Too easy. Next question?

[robertw]

Hedley is correct, however, it would be wise to follow some kind of system to monitor the condition of your engine health.

The regulations do not require you to do anything other than an annual inspection and CAR 625 Appendix C items, however, if you are concerned with your own safety and that of whoever you might take along as passengers, you should pay a little more attention to the condition of your engine if it's past it's TBO. There is a reason manufacturers give these recommendations!

Flight training units and commercial operators, should they wish to fly past engine TBO have to institute an "Engine on Condition Maintenance Program" outlined in Airworthiness Notice AN B041, edition 4. See the link below.

http://www.tc.gc.ca/eng/civilaviation/s ... 41-549.htm

This program enables you to keep a close eye on what your engine is doing. It would be good sense to at least adopt some of the pieces of this program into your schedule like the oil sampling for example.

[Hedley]

TBO is a statistical concept and as such can be pretty tricky and slippery, and only makes sense in the context of commercial operators who have some kind of consistent usage pattern.

My favorite statistic is that a man with his head in the freezer and his feet in the stove, is on average "comfortable". Kind of meaningless.

TBO is quite meaningless to a private operator. For example, let's say you're looking at importing a C172 from the USA. Cnd dollar is pretty strong, right? And it's got a perfect engine - 5 years since factory new, and only 100 hours on it. What could be wrong with that? Well, if you dig deeper into the logs, you might discover that the aircraft flew 100 hrs in the first year after the overhaul, and then sat unused for 4 years without being pickled. It's now totally destroyed from internal corrosion, but beautifully within both flight time and calendar TBO.

I've flown a twin with one engine 5500 SMOH, and it ran fine. I've flown engines that haven't been overhauled in 50 years, that run fine. Flight time and calendar TBO are completely, totally irrelevant to private ops.

I am not a big fan of oil analysis. Or oil filters, for that matter. But I do like to peek in the oil pressure screen at annual. If there's metal in there - and it will give you plenty of warning - then you have some thinking to do.

I don't know why people panic about metal in the oil. You can have an awful lot of stuff broken on an engine - eg broken rings - and it will run just fine, but it will consume a bit of oil (warning sign). If the bearings are worn, the oil pressure will be low. This is not rocket science.

What you have to pay attention to, are the hot bits. The exhaust valve in particular. You want to look at the face for cracks, and the stem for necking.

A problem with your exhaust valves can ruin your whole day, which is NOT the case with broken rings (eg).

You drop an exhaust valve, you will notice it!

I have only been operating and maintaining aircraft piston engines for 40 years now, so I probably don't know very much compared to the young people here.

[robertw]

Point taken Hedley. I was not intending to take away from your experience, however, your original post left the impression that the OP should just run his engine until it gave up the ghost. As you stated, engine TBO is a subjective thing that depends greatly upon usage and storage. I was merely poining out that one should not just blindly run their engine past TBO without a few checks and balances.

[Hedley]

I was merely poining out that one should not just blindly run their engine past TBO without a few checks and balances

Absolutely! My point was that you should be concerned with your health of your engine, regardless of hours flown or years SMOH.

Warning signs to look for:

1) when you pull the prop through, one cylinder goes "whoosh"
2) oil consumption increases
3) oil gets black really quickly
4) oil pressure decreases
5) oil temperature increases
6) morning sickness. Exhaust valve sticking?
7) mag drop. Plug filling up with lead? Harness lead damaged? Mags worn?
8) static rpm
9) look at the spark plugs. Bottom plug oily means rings are wearing, top plug oils means pull the jug
10) metal in the oil pressure screen. Cam lobes spalling? Pistons scuffing? Bearings toast?
11) mechanical condition of exhaust valve (this is really, really important)

I worship at the Church Of The Internal Combustion Engine. Our litany is Suck / Squeeze / Bang /Blow. Your engine will talk to you, in so many different ways. Listen to it.

[robertw]

'Nuff said Hedley.

[corroded_camshaft]

1) when you pull the prop through, one cylinder goes "whoosh"

I've got one cylinder that does make some kind of small squeal when I pull the prop, not sure if I ever brought it up to my AME though. Been like that since I've owned the plane, which includes a tear down/repair/rebuild last year.

What would be the cause of that?

[Hedley]

Do you have mice in your hangar?

[corroded_camshaft]

I tie-down in the grass, but I keep an engine cover on in winter, and plugs in summer.

[iflyforpie]

I tie-down in the grass, but I keep an engine cover on in winter, and plugs in summer.

Given that your engine had a 'corroded camshaft' I would think something like that would be corrosion/pitting on the cylinder walls. How did the jugs look when they came off?

[corroded_camshaft]

To me they looked fine, but the shop told me there was a bit of corrosion in them. Cylinders were grinded, new rings installed, new camshaft, new pushrods, new lifters, new gear in the oil pump.

[c170b53]

Sounds like you need a new handle.

[cgzro]

Given that your engine had a 'corroded camshaft' I would think something like that would be corrosion/pitting on the cylinder walls. How did the jugs look when they came off?

Not necessarily, the camshaft (at least on a lycoming) is located way up top and is the first place to dry up. Its especially bad for a tail dragger as the oil runs off the front cam lobes first as they are almost now the highest point on the engine when parked tail low on the ground. Too bad we can't turn an airplane upside down on the ground every week. It would fix lots of rust problems

What does happen though is the corrosion takes away the hardened surface so the camshaft and lifters start to spald (make metal flakes), those flakes drop on the piston skirts and now start to scratch the upper surface of the piston walls etc.

Its expensive to fly, its even more expensive not to fly

[Hedley]

Exactly. Worst thing you can do to a Lycoming is not fly it.

[iflyforpie]

Given that your engine had a 'corroded camshaft' I would think something like that would be corrosion/pitting on the cylinder walls. How did the jugs look when they came off?

Not necessarily, the camshaft (at least on a lycoming) is located way up top and is the first place to dry up. Its especially bad for a tail dragger as the oil runs off the front cam lobes first as they are almost now the highest point on the engine when parked tail low on the ground. Too bad we can't turn an airplane upside down on the ground every week. It would fix lots of rust problems

What does happen though is the corrosion takes away the hardened surface so the camshaft and lifters start to spald (make metal flakes), those flakes drop on the piston skirts and now start to scratch the upper surface of the piston walls etc.

Its expensive to fly, its even more expensive not to fly

Yes, but the cylinders are a dry place on every engine (unless you've got ring or guide problems), including the more sensible Continentals and Lycomings (TIO-541s) which put the camshaft on the bottom.

[cgzro]

True, but you can replace a cylinder, or all cylinders at far lower cost than the camshaft which requires complete removal/rebuild of the bottom end.

Peter

[iflyforpie]

Agreed, but I was just offering a possible cause to a 'squeaky' cylinder from a previously neglected engine.

Actually, I just topped an O-540 a year ago on a PA-28-235. Leak-downs were great (typical Lycoming mid 70s). but it was going through oil like crazy. Just over 100 hours on the engine in 12 years since overhaul.

Pulling the engine apart, the camshaft was in perfect shape. The cylinders actually weren't too bad either... for rust anyways. We're a pretty dry climate here, but what surprised me was that the pushrods were covered in rust. I suppose maybe the camshaft was saved due to the extreme infrequence of operation.

Back to the problem at hand, we took the rings off the pistons, and you could bend them into an 'S' shape without them breaking. Wrong, really wrong. The shop went to re-hone the cylinders and they went through five thou like butter. Junk, either from manufacturing defect (ECi, not the best) or overheating. The owner actually managed to get warranty out of them, and got a brand-new set for a song.

I told him to fly the plane more. He was really proud that he put on 25 hours last year.