TBO and rental ops

[avbug]

The other question is you have the 2000 hrs (in the case of the 98 172 you mentioned) as a hard limit established on the engine. If you go beyon it when is the next limit you are going to use? 100 more hours, 200 more hours? until it quits?

Good comments, but remember that TBO isn't a hard limit when operating strictly under Part 91. It's a recommendation. The engine is operated on-condition. Replacing at TBO or sooner isn't a bad thing, but TBO is not a limitation nor a gaurantee. And after the first run, the concept of TBO is nebulous at best.

 

[nosehair]

The question you need to ask yourself isn't weather getting away with it is lega, but how much of your life, that of your student, that of those on the ground, your reputation, your certificate, and your future, present, and past, you're willing to bet on the matter.

...aaaahh, pretty much all of it,...that's how I do every flight.
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[nosehair]

It's the compressions you need to worry about. Don't worry about the oil seals or oil pump...they'll far outlast the compressions. Engines are designed so that nothing will go wrong so long as the compressions are good.

Hot Dang it!! I knew it!...thass what I been thinkin', an' now I know it!
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[USMCmech]

Compresion tests by themsleves mean nothing.

I have seen data from tests of engines that tested only 30/80 yet still produced full rated Hp. OTOH, as lycoming has found out recently, a crackshaft can snap with zero warning.

Re: TBO

TBO is the life expectency of the engine, it is not a recomedtion to do anything at all when the magic numbers roll around. If your engine has reached TBO and is running strong it stands a very good chance of running for quite a bit longer. A freshly overhauled engine (regardless of who did it) is much more likely to fail durring it's first 100 hours.

The average age that an American male need bypass surgery (AKA an overhaul) is 50-55. Does than mean that you should have open heart surgery just because you reach a certian age, of course not! The same logic applys to your engine.

FYI if you live to 61 you are most likely to make it to 90.


I personally know a guy who flys pipeline patrol in a C-172 which has an engine with 7000 hours since overhaul. He flys it almost daily, takes excelent care of it, monitors it closely with oil anylsis, knows EXACTLY how long his takeoff roll should be for any given weather conditions, ect.

I also met a guy who had an engine failure in a Bonanza. He couldn't understand why the engine had failed since it had so little time since new(less than 800hrs I think). The fact that this was a 25 year old plane and had sat untouched for 9 of those didn't seem to concern him. He hadn't had the oil checked for metal when it was changed.

TBO is just a number

Read these articles from avweb.

http://www.avweb.com/news/columns/187037-1.html

http://www.avweb.com/news/columns/188758-1.html

http://www.avweb.com/news/columns/190242-1.html

 

[A Squared]

And after the first run, the concept of TBO is nebulous at best.

And as a side note, a zero-time factory overhaul is beyond nebulous, and into the realm of downright deceptive. Zero time engines are assembled from piles of major components of completely unknown history. your "zero time" engine may have case halves with 15,000 hours and a crank that has 10,000, rods that have 17,000. You don't know, and neither does the factory because the records have been discarded.

 

[NYCPilot]

A freshly overhauled engine (regardless of who did it) is much more likely to fail durring it's first 100 hours.

I think I've heard this before, but what are the general reasons or causes for an engine to fail after an overhaul within the first 100 hrs.

 

[avbug]

And as a side note, a zero-time factory overhaul is beyond nebulous, and into the realm of downright deceptive. Zero time engines are assembled from piles of major components of completely unknown history. your "zero time" engine may have case halves with 15,000 hours and a crank that has 10,000, rods that have 17,000. You don't know, and neither does the factory because the records have been discarded.

True story. Overhaul doesn't mean much...the parts have been inspected and meet tolerance, and that's about it. A factory job may have new parts, but a lot will be reused...most major parts, in fact.

Even a typical "top" overhaul reuses the second most stressed part of the engine...the connecting rods as a matter of course.

Ignorance, for most, is bliss.

Why do engines tend to fail more right off the bat? Most things fail new...they haven't been proven yet. Older equipment, excepting unusual streses or undetected design or manufacturing flaws, tends to be more tried and tested, and whatever is going to break has already broken. Very notable exceptions to that exist, but it's those first few hours out of the shop when thing begin to loosen, parts begin to work against each other that haven't done so before, and stresses can become manifest.

All a new engine says to me is "guess which part is gonna break first?"

 

[pilotmiketx]

There is a reason why that TBO is established. Especially in an environment where the engine is getting abused I am not even sure if an engine can make it to the TBO in a very healthy manner.

The engines that make it to TBO and past are the ones that are run hard and run regularly. I don't expect the engine on my 170 that flies less than 100 hrs/yr to make it anywhere near TBO (nor do I plan on owning it that long.) All of the 135 freight and flight school planes that I flew would make it past TBO. It wasn't magic, they were just flying 100 hours/mo.