Going over TBO....flight school

[kellwolf]

Can, have, and would again. It's more the MX dept than the engine, IMO. If the compression checks are good, there's really no reason to spend unnecessary cash to fix what isn't broken.

As for civil suits if you crash into a house.....aim for a field if the engine quits, which could (and has) happened in engines that are within TBO limits.

[killbilly]

There is a pretty significant price difference in the market right now between a plane within, say 250 hours of the recommended overhaul and one which has 600 or more hours to go. Take roughly identical 172s with comparable interiors and avionics stacks and the lower-time aircraft is going to be priced $10K higher.

Not saying it's right or wrong, but there is at least a perception in the market that the price of the overhaul is a given and will have to be done.

I imagine this may have something to do with insurance, too, as mojo said.

[TFaudree_ERAU]

Overhauling at TBO with good vitals is like the TSA making you take your shoes off. It may make the some people feel better, but its pointless.

[DE727UPS]

Insurance companies don't care. The policy says the airplane must be "airworthy" and nothing in the FAR's, for part 91 flying, suggests an over TBO engine is unairworthy.

[USMCmech]

Originally Posted by TFaudree_ERAU

Overhauling at TBO with good vitals is like the TSA making you take your shoes off. It may make the some people feel better, but its pointless.

I maintain that it is more like having a 55 year old man get bypass surgerydespite his low blood pressure.


I would far rather fly a engine with 3000 hours than one with 20.

[mojo6911]

Originally Posted by DE727UPS

Insurance companies don't care. The policy says the airplane must be "airworthy" and nothing in the FAR's, for part 91 flying, suggests an over TBO engine is unairworthy.

Negative. I know of two flight schools who just renewed and had to get rid of airplanes over 10% of TBO.

[calcapt]

Originally Posted by USMCmech

I would base it on the oil anylisis more than anything else.

Compression tests can vary wildly on the same engine from one flight to the next. In fact if you get a low reading it is SOP to run the engine for a bit and redo the test.


I personally would not EVER overhaul an engine that wasn't not showing signs of metal in the oil, or a drop in power, or some other symptom of a problem.

I knew a guy who flew pipline patrol in a C-172 with 7000 hours on the motor.
It was in perfect operating condition and he had no plans of ever spliting the case.


OTOH, I would give the possible liability argument some credence if I were leasing it out to a school. This is the sort of thing that a PI lawyer would seize upon whlie asking for .5 mill.

Originally Posted by Berkut

I wish there was a poll option to show who among the voters has maintenance experience and how they voted.

I completely agree with USMCmech and I have been a practicing A&P for 26 years.

[bLizZuE]

knowing what it means, I don't see an option for "depends".

[slushie]

Given the discussion, I am voting for "let it ride."

As far as legalism goes, TBO is recommended, so going past it should carry the same weight as not following through on a service bulletin.

[Realms09]

If you know the airplane I can see how y'all would be comfortable with it. However, I do not see how a renter strolling into a FBO should or would trust an unknown A&P to not do things "by the book."

[TFaudree_ERAU]

Originally Posted by Realms09

However, I do not see how a renter strolling into a FBO should or would trust an unknown A&P to not do things "by the book."

By the book doesn't necessarily mean to overhaul at the recommended interval. To me, by the book means "does the engine have good compression, low oil consumption and good performance, even if it is at 2000 hours".

[Berkut]

Here's a rather timely article on the subject:
http://www.avweb.com/news/savvyaviat..._195241-1.html

[slushie]

Originally Posted by Berkut

Here's a rather timely article on the subject:
http://www.avweb.com/news/savvyaviat..._195241-1.html

Wow!
So I'm thinking that the best option for a first-time aircraft owner would be to get an airplane with a 500-hour engine.

[Berkut]

Hmmm, that sounds like a service I can provide. "Bring me your brand-new aircraft engine and I will fly off those dangerous first few hours. Why risk infant mortality? Let me do it for you!" That's how nice I am.

I'm way more nervous flying a freshly overhauled engine than a really old one. No matter how much you check and double check that you did it right, there's always that nagging feeling that you did something wrong...

[Realms09]

Originally Posted by TFaudree_ERAU

By the book doesn't necessarily mean to overhaul at the recommended interval. To me, by the book means "does the engine have good compression, low oil consumption and good performance, even if it is at 2000 hours".

My concern would not be just with the performance parameters you listed. Even if the engine is nominally running great it could be in need of overhaul due to fatigue damage. Cyclic loading reduces metal strength from its ultimate single limit load, and the more cycles you put it under, the weaker it is. Past a certain number of cycles cracks will develop, perhaps beneath the surface. Cracks lead to stress concentrations, and stress concentrations give way to failure. Even if you use ultrasound testing for subsurface cracks at 2000 hours and you find none, fatigue is accumulative. Past a certain number of hours, things just need to be replaced for no other reason than they have been in service for that many hours (cycles). Engine manufacturers have chosen 2000 hours as indicative of that point.

[Berkut]

Originally Posted by Realms09

Past a certain number of hours, things just need to be replaced for no other reason than they have been in service for that many hours (cycles).

Which parts are you speaking of, specifically?

[vheissu]

Reading through this is making me think about proper break in procedures. I ferried a brand new 172 from Florida to California, and was told to go full throttle the whole way. 1 AM somewhere over the middle of Texas would have been the worst place to have something go wrong..

[Realms09]

Originally Posted by Berkut

Which parts are you speaking of, specifically?

Anything that undergoes cyclic loading - pistons, connecting rods, valves, etc. (what I presume are usually replaced in an overhaul).

"I ferried a brand new 172 from Florida to California, and was told to go full throttle the whole way. 1 AM somewhere over the middle of Texas would have been the worst place to have something go wrong.."

There are worse places to be than the middle of Texas. SoCal comes to mind...